Transcriber's Note: Italic text is denoted by _underscores_ and bold
text by =equal signs=.
THE BRITISH WOODLICE.
This monograph first appeared in the "Essex Naturalist" (Volume XIV.,
1905-6) and has been republished by special arrangement with the
Council of the Essex Field Club.
THE BRITISH WOODLICE.
BEING
A MONOGRAPH OF THE TERRESTRIAL ISOPOD CRUSTACEA
OCCURRING IN THE BRITISH ISLANDS.
BY
WILFRED MARK WEBB, F.L.S.,
_Lecturer on Biology and Nature Study to the Surrey County Council,
Honorary Secretary of the Selborne Society, Sometime, Senior Assistant
Lecturer on Biology to the Essex County Council, and Editor of the
Journal of Malacology, Joint Author of_ "Eton Nature Study and
Observational Lessons."
AND
CHARLES SILLEM.
WITH TWENTY-FIVE PLATES AND FIFTY-NINE FIGURES IN THE TEXT.
LONDON:
DUCKWORTH & CO.,
3, HENRIETTA STREET, COVENT GARDEN.
1906.
PREFACE.
In Professor Sars' "Crustacea of Norway," quite a number of the British
species of woodlice are figured in detail and described in English, but
few copies of this fine work are to be met with in our country. The
Rev. Canon Norman has from time to time published notes on the British
species in "The Annals and Magazine of Natural History;" these are,
however, scattered, and contain but few figures, while other literature
that exists is out of date. Under these circumstances, we have thought
that the following account and figures of all the British species would
be useful to those anxious to work at the woodlice, and might also
encourage others to pay attention to the distribution and habits of the
interesting tribe to which they belong.
The writers would welcome any corrections or additions in view of a
second edition.
W.M.W.
C.S.
ODSTOCK, HANWELL, _December, 1905_.
CONTENTS.
PAGE
Introduction 1
Geological history 1
External structure and appendages 2
Alimentary canal 6
Circulatory system 7
Excretory system 7
Nervous system 8
Reproductive organs 8
Development 9
Habits and Economic considerations 12
Local names 15
Methods of collections and preservation 16
Classification 17
Scheme of classification and synopsis of generic characters 18
British Species 19
Section--Ligiæ 19
Family--Ligiidæ 19
Genus--Ligia Fabricius 19
_Ligia oceanica_ Linzé 19
Genus--Ligidium Brandt 21
_Ligidium hypnorum_ Cuvier 21
Family--Trichoniscidæ 22
Genus--Trichoniscus Brandt 22
_Trichoniscus pusillus_ Brandt 22
_Trichoniscus vividus_ Koch 23
_Trichoniscus roseus_ Koch 24
Genus--Trichoniscoides, Sars 25
_Trichoniscoides albidus_ Budde-Lund 25
Genus--Haplophthalmus Schobl 26
_Haplophthalmus mengii_ Zaddach 26
_Haplophthalmus danicus_ Budde-Lund 27
Family--Oniscidæ 27
Genus--Oniscus Linné 27
_Oniscus asellus_ Linné 27
Genus--Philoscia Latreille 29
_Philoscia muscorum_ Scopoli 29
_Philoscia couchii_ Kinahan 30
Genus--Platyarthrus Brandt 30
_Platyarthrus hoffmannseggii_ Brandt 30
Genus--Porcellio Latreille 32
_Porcellio scaber_ Latreille 32
_Porcellio pictus_ Brandt and Ratzeburg 33
_Porcellio dilatatus_ Brandt 33
_Porcellio rathkei_ Brandt 34
_Porcellio laevis_ Latreille 35
_Porcellio ratzeburgii_ Brandt 36
Genus--Metoponorthus Budde-Lund 37
_Metoponorthus pruinosus_ Brandt 37
_Metoponorthus cingendus_ Kinahan 38
Genus--Cylisticus Schnitzler 38
_Cylisticus convexus_ De Geer 39
Family--Armadillidiidæ 40
Genus--Armadillidium Brandt 40
_Armadillidium nasatum_ Budde-Lund 40
_Armadillidium vulgare_ Latreille 41
_Armadillidium pulchellum_ Zencker 42
_Armadillidium depressum_ Brandt 43
Distribution of species 43
Conclusion 43
Bibliography 49
LIST OF FIGURES.
PLATES I.-XXV. with a List, will be found at the end of the Book.
FIGURE. PAGE.
1. Parts of the body (_Oniscus asellus_) 2
2. The first antenna (_Oniscus asellus_) 2
3. The second antenna (_Oniscus asellus_) 3
4. The underside of the head (_Oniscus asellus_) 3
5. The mandibles (_Oniscus asellus_) 4
6. The first maxillae (_Oniscus asellus_) 4
7. The second maxillae (_Oniscus asellus_) 4
8. The fused maxillipeds (_Oniscus asellus_) 4
9. The "upper lip" (_Oniscus asellus_) 5
10. The "lower lip" (_Oniscus asellus_) 5
11. A typical thoracic segment (_Oniscus asellus_) 5
12. The fifth thoracic segment of a female
(_Oniscus asellus_) 5
13. The underside of the abdomen of a female
(_Oniscus asellus_) 6
14. A typical abdominal appendage
(_Oniscus asellus_) 6
15. The first abdominal appendage of the male
(_Oniscus asellus_) 6
16. The second abdominal appendage of the male
(_Oniscus asellus_) 6
17. The alimentary canal (_Oniscus asellus_) 7
18. The circulatory system (_Oniscus asellus_) 7
19. The nervous system (_Oniscus asellus_) 8
20. Female reproductory organs (_Oniscus asellus_) 8
21. The male reproductory organs (_Oniscus asellus_) 9
22. The fertilized egg (_Porcellio scaber_) after Roule 10
23. The fertilized egg seen in section
(_Porcellio scaber_) after Roule 10
24 to 31. The development of a woodlouse
(_Porcellio scaber_) after Roule 10
32. Embryo of the woodlouse showing the three divisions of the
intestine separately developed (_Porcellio scaber_)
after Roule 11
33. Embryo of the woodlouse showing traces of the segments
(_Porcellio scaber_) after Roule 11
34. An embryo woodlouse ready to be hatched
(_Porcellio scaber_) after Roule 11
35. Flagellum and last peduncular joint of the antenna of
_Ligia oceanica_ 12
36. Flagellum and last peduncular joint of the antenna of
_Ligidium hypnorum_ 13
37. Flagellum and last peduncular joint of the antenna of
_Trichoniscus pusillus_ 23
38. Flagellum and last peduncular joint of the antenna of
_Trichoniscus vividus_ 24
39. Flagellum and last peduncular joint of the antenna of
_Trichoniscus roseus_ 24
40. Flagellum and last peduncular joint of the antenna of
_Trischoniscoides albidus_ 25
41. Flagellum and last peduncular joint of the antenna of
_Haplophthalmus mengii_ 26
42. Flagellum and last peduncular joint of the antenna of
_Haplophthalmus danicus_ 27
43. Flagellum and last peduncular joint of the antenna of
_Oniscus asellus_ 28
44. Flagellum and last peduncular joint of the antenna of
_Philoscia muscorum_ 29
45. Flagellum and last peduncular joint of the antenna of
_Philoscia couchii_ 30
46. Flagellum and last peduncular joint of the antenna of
_Platyarthrus hoffmannseggii_ 31
47. Flagellum and last peduncular joint of the antenna of
_Porcellio scaber_ 32
48. Flagellum and last peduncular joint of the antenna of
_Porcellio pictus_ 33
49. Flagellum and last peduncular joint of the antenna of
_Porcellio dilatatus_ 34
50. Flagellum and last peduncular joint of the antenna of
_Porcellio rathkei_ 35
51. Flagellum and last peduncular joint of the antenna of
_Porcellio laevis_ 35
52. Flagellum and last peduncular joint of the antenna of
_Porcellio ratzeburgii_ 36
53. Flagellum and last peduncular joint of the antenna of
_Metoponorthus pruinosus_ 37
54. Flagellum and last peduncular joint of the antenna of
_Metoponorthus cingendus_ 38
55. Flagellum and last peduncular joint of the antenna of
_Cylisticus convexus_ 39
56. Flagellum and last peduncular joint of the antenna of
_Armadillidium nasatum_ 40
57. Flagellum and last peduncular joint of the antenna of
_Armadillidium vulgare_ 41
58. Flagellum and last peduncular joint of the antenna of
_Armadillidium pulchellum_ 42
59. Flagellum and last peduncular joint of the antenna of
_Armadillidium depressum_ 43
THE BRITISH WOODLICE.
=Introduction.=--Having finished a somewhat exhaustive list of the land
and fresh-water molluscs of Essex,[1] one of the present writers felt
that if he were to make any further contributions of importance to a
knowledge of the fauna of that interesting county, he must turn his
attention to some other group of animals. It seemed most fitting that
some creatures should be chosen which are commonly met with during the
search for molluscs. Centipedes, millepedes, and woodlice fulfilled
these conditions, and all were collected, but as only seventeen
species of woodlice had at the time been found in England, it was
deemed advisable to study these in detail to begin with. The present
contribution is the result of the undertaking, and we have thought that
a general consideration of the British Woodlice, with careful drawings
from nature of all the species now known from this country, ought to
lead to a more general study of these interesting creatures and their
habits.
=Position in the scheme of classification.=--The Woodlice belong to
an immense group of invertebrate animals known as the Arthropoda, the
bodies of which are segmented and provided with jointed appendages for
purposes of walking, swimming, and feeding. Of this group, two large
divisions are recognized. The first contains the forms which breathe
by means of air-tubes, such as the Insects; and the second has been
constituted for Crustacea, which breathe by means of gills. The latter
are, of course, adapted more especially for a life in water, but here
and there we come across examples so modified that they can exist in
air. The land-crabs are a case in point, and so are the Woodlice. These
belong to an order which contains many fresh-water and marine species,
known as the Isopoda.
=Geological history.=--The known history of the order is a long one,
for remains occur in the Old Red Sandstone (Devonian) of Herefordshire,
and in the Coal Measures. (79)[2]. A form which has been named
_Archæoniscus brodiei_, and is said to be referable to the recent
family Aegidae which is found in some numbers in the Purbeck Beds
(Upper Jurassic), of this country (47). Fossil Isopods have also been
recorded from the Oolite and from the Oligocene (Isle of Wight).
Turning to the Woodlice proper, we find that they first make their
appearance in the Miocene (of Oenigen and Baden), and occur also
in amber (79); while examples of genera, such as _Oniscus_ and
_Porcellio_, have been discovered in late Tertiary deposits (47).
=External structure and appendages.=--Woodlice agree in being of a
somewhat oval form, and their bodies are arched, the curve varying in
different genera and species. A _head_ is to be distinguished; behind
this comes the _thorax_ of seven segments which are often considerably
broader than the six succeeding ones which form the _abdomen_ (see fig.
1.)
[Illustration: FIG. 1.--PARTS OF THE BODY. (_Oniscus asellus._)]
The head carries two _large antennae_ (fig. 3) which are very evident,
and a careful search with a lens will reveal a second and minute pair
(the _smaller antennae_) situated between the base of the others, and
really anterior to them. (figs. 2 and 4.)
[Illustration: FIG. 2.--THE FIRST ANTENNA. (_Oniscus asellus._)]
The larger antennae are customarily bent at certain points, and we can
distinguish a terminal part, or _flagellum_, and a basal part, the
_peduncle_ (fig. 3). The number of joints in these structures, which
varies in different genera and species, forms a useful classificatory
character, and the relative length of the component parts is of
considerable value in distinguishing species.
[Illustration: FIG. 3.--THE SECOND ANTENNA. (_Oniscus asellus._)]
There are four pairs of mouth appendages--namely the jaws or
_mandibles_ (fig. 5), the _first maxillae_ (fig. 6), the _second
maxilla_ (fig. 7), and the _maxillipeds_ (fig. 8). When the head is
examined from the underside the last of these organs will be seen
first, covering in the others.
[Illustration: FIG. 4.--THE UNDERSIDE OF THE HEAD. (_Oniscus
asellus._)]
A small median plate attached to the front of the head has been called
"_the upper lip_" (fig. 9), while inside the mouth appendages is a
little bilobed structure "_the lower lip_" (fig. 10).
[Illustration: FIG. 5.--THE MANDIBLES. (_Oniscus asellus._)]
Before leaving the external features of the head, we must allude to
the pair of _eyes_ which are usually present, though never raised on
stalks. In the Common Woodlouse (_Oniscus asellus_, from which all
our figures to illustrate structure have been made), as in many other
species, the eyes are compound (fig. 4), but in some forms these are
simple.
[Illustration: FIG. 6.--THE FIRST MAXILLAE. (_Oniscus asellus._)]
[Illustration: FIG. 7.--THE SECOND MAXILLAE. (_Oniscus asellus._)]
[Illustration: FIG. 8.--THE FUSED MAXILLIPEDS. (_Oniscus asellus._)]
Each of the seven joints of the thorax bears a pair of _walking legs_
(fig. 11), and in the female at the time when the eggs are laid, a pair
of plates (fig. 12) arises on segments II. to V. These plates together
form a brood pouch, in which the eggs are carried (fig. 12) until
they are hatched, and in which the young ones remain for some time
afterwards.
When we examine the abdomen, we find that the appendages are
plate-like, with the exception of the last pair (fig. 13), and they all
agree in having two divisions, an arrangement which would prove awkward
in limbs used for walking or feeling.
[Illustration: FIG. 9.--THE "UPPER LIP." (_Oniscus asellus._)]
[Illustration: FIG. 10.--THE "LOWER LIP." (_Oniscus asellus._)]
[Illustration: FIG. 11.--A TYPICAL THORACIC SEGMENT. (_Oniscus
asellus._)]
[Illustration: FIG. 12.--THE FIFTH THORACIC SEGMENT OF A FEMALE.
(_Oniscus asellus._)]
The inner plate (or endopodite) is in structure a _gill_, but the blood
that passes through it, is enabled to take up oxygen from moist air,
while the outer division (or exopodite) acts as a protecting cover
(fig. 14). In _Porcellio_, air-tubes (_tracheae_) may be present (see
below).
[Illustration: FIG. 13.--THE UNDERSIDE OF THE ABDOMEN OF A FEMALE.
(_Oniscus asellus._)]
In the male, the first two pairs of abdominal appendages are specially
modified, the inner divisions (endopodites) being long and pointed
(figs. 15 and 16). The last pair, or tail appendages, in the male are
often considerably larger than in the female, and the form of these
structures is sometimes of value in classification.
[Illustration: FIG. 14.--A TYPICAL ABDOMINAL APPENDAGE. (_Oniscus
asellus._)]
[Illustration: FIG. 15.--THE FIRST ABDOMINAL APPENDAGE OF THE MALE.
(_Oniscus asellus._)]
[Illustration: FIG. 16.--THE SECOND ABDOMINAL APPENDAGE OF THE MALE.
(_Oniscus asellus._)]
=Alimentary canal.=--The main portion of the alimentary system is,
practically speaking, a straight tube (fig. 17). Its first part (not
shown in the figure) is a narrow gullet, which after passing through
the nerve collar dilates to form a sort of stomach. Into this the
secretion of four digestive glands is poured by two ducts. These glands
have a somewhat striking appearance, being yellow tubes spirally
coiled, and they end blindly. From the stomach the intestine runs to
the hinder end of the body and passes under the heart.
=Circulatory system.=--The blood being aërated in the abdominal
appendages, we find that the heart is situated towards the hinder end
of the body (fig. 18). Three main arteries supply the thorax and head,
while the blood is brought from the gills to the heart.
=Excretory system.=--The excretory organs consist of a (_a_) pair of
so-called "shell glands," which are considered to be the equivalents
of the excretory tubes or nephridia of annelid worms. In the woodlouse
these excretory organs open on the second pair of maxillae. They are
composed of a tube (_sacculus_) closed at one end and more or less bent
upon itself (5, p. 261) which communicates with a _labyrinth_ that
is provided with an excretory orifice. Matters are eliminated by the
_epithelial cells_ [the histology has been described and figured in
_Ligidium hypnorum_ (66)], which are very large in _Ligia oceanica_.
[Illustration: Fig. 17.--THE ALIMENTARY CANAL. (_Oniscus asellus._)]
[Illustration: Fig. 18.--THE CIRCULATORY SYSTEM. (_Oniscus asellus._)]
(_b_) Masses of cellules in the head, very greatly developed in _Ligia
oceanica_ (but numbering scarcely more than ten in _Oniscus asellus_),
which have no external opening. They also function as excretory organs
(5, p. 263), and have been called "cephalic nephrocytes."
[Illustration: FIG. 19.--THE NERVOUS SYSTEM. (_Oniscus asellus._)]
(_c_) Other "branchial nephrocytes" are situated on the dorsal surface
between the last thoracic and the first abdominal segments, as well as
between those that follow, with the exception of the last two; they are
in distinct patches, one on each of the middle line in _Ligia_, but
more or less continuous in _Oniscus_ (5, p. 265).
(_d_) The digestive glands have also been shown to be excretory (5, p.
270).
=Nervous system.=--The nervous system consists of _paired ganglia_
in the head, above the alimentary canal which send off nerves
(_commissures_) that meet below, to form a _double nerve cord_ with
ganglia at intervals (see fig. 19).
[Illustration: FIG. 20.--FEMALE REPRODUCTORY ORGANS. (_Oniscus
asellus._)]
=Reproductive organs.=--In the female there are a pair of _ovaries_ in
the positions shewn in fig. 20; and _ducts_ run to the underside of the
fifth thoracic segment.
The openings are very difficult to identify, and Lereboullet (39, p.
113) was unable to find them. It is obvious that the openings must be
underneath the plates that form the egg pouch, and as a change of skin
is required to set these free, it would appear that at ordinary seasons
the ducts from the ovaries are closed. The writers have been able to
determine from external examination of specimens which had moulted and
were about to lay eggs, that the oviducts at such time open to the
inside of the base of each walking leg on the fifth segment. In similar
specimens the oviducts were also followed to the opening from within.
The _brood pouch_ has already been described.
The male organs consist of six _testes_ arranged in two pairs, each
of which is provided with a _reservoir_ (see fig. 21). The efferent
ducts from the two reservoirs unite at the base of the thorax to form a
common duct (or "penis").
[Illustration: FIG. 21.--THE MALE REPRODUCTORY ORGANS. (_Oniscus
asellus._)]
=Development.=--The eggs, in the common species of woodlice, at
least, are laid at the beginning of summer, and are retained in the
brood pouch, where they undergo their development. The process has
been recently traced with great care by Professor Louis Roule (58) in
_Porcellio scaber_ and the description which follows is based upon his
researches.
As, practically speaking, the larval stages are passed within the egg,
and there is no free embryo differing in form from the parent, it is
necessary for the young creatures to be well supplied with nutritive
material. In fact, the bulk of the large egg is made up of _food-yolk_,
on the outside of which the _formative protoplasm_ is disposed in
irregular patches. In the fertilized ovum, one of the latter, which
lies in a particular position at the end, is found to be larger than
the others (see fig. 22). It contains the nucleus of the egg-cell (see
fig. 23) and is called the _cicatricula_. This is the only portion of
the egg which divides and produces _nucleated cells_. It is these which
gradually spread all over the surface of the food-yolk, forming a layer
known as the _blastoderm_, which is at first but one cell thick (see
figs. 24, 26, and 28).
Before, however, the food-yolk is quite closed in, a differentiation
into two layers--the _pro-ectoderm_ and _pro-endoderm_--takes place
(see fig. 25) and rudiments of the first two pairs of _appendages_
appear (see fig. 26). Moreover, the cells of the ectoderm change their
shape and begin to multiply at two points to form the beginnings of the
cerebral ganglia and the nerve cord respectively.
[Illustration: FIG. 22.--THE FERTILIZED EGG (_Porcellio scaber_), AFTER
ROULE.]
[Illustration: FIG. 23.--THE FERTILIZED EGG SEEN IN SECTION (_Porcellio
scaber_), AFTER ROULE.]
As the blastoderm closes over the food-yolk, two more appendages arise
and these are soon followed by others (see fig. 28). A depression
appears at the point where the blastoderm closed and internally the
pro-endoderm or inner layer is differentiated into two--the _endoderm
proper_ and the _mesoderm_ (see fig. 29). The former begins to grow
so that its edges unite to form the middle part of the intestine (see
fig. 29) seen from the outside in fig. 30. The depression already
mentioned grows deeper, forming a tube which is the hind portion of the
_intestine_, while at the anterior end of the embryo the front part of
the intestine is similarly formed (see fig. 30). By this time also all
the nineteen appendages have made their appearance and the mesoderm,
(which has grown considerably, to form the beginnings of the muscles)
has sent prolongations into each of them. About this time, spaces (see
fig. 31) are formed in the muscular mesoderm which are all that remain
of the _true body cavity_ characteristic of animals above the level of
the jelly fish, and in these spaces the blood ultimately circulates.
_SURFACE VIEWS._
[Illustration: FIG. 24.]
[Illustration: FIG. 26.]
[Illustration: FIG. 28.]
[Illustration: FIG. 30.]
_OPTICAL SECTIONS._
[Illustration: FIG. 25.]
[Illustration: FIG. 27.]
[Illustration: FIG. 29.]
[Illustration: FIG. 31.]
THE DEVELOPMENT OF A WOODLOUSE (_Porcellio scaber_), AFTER ROULE.
Figs. 24, 26, 28, 30, are Surface Views, and figs. 25, 27, 29, 31,
which indicate slightly later stages respectively than the others, are
of egg seen in Optical Section.
The body next alters somewhat in shape and the three divisions of
the intestine approach one another (see fig. 32) previous to their
junction. As may be imagined during these processes the food-yolk has
gradually been used up and the space which it occupied taken by the
internal organs, which we have mentioned.
[Illustration: FIG. 32.--EMBRYO OF THE WOODLOUSE SHOWING THE THREE
DIVISIONS OF THE INTESTINE SEPARATELY DEVELOPED (_Porcellio scaber_),
AFTER ROULE.]
[Illustration: FIG. 33.--EMBRYO OF THE WOODLOUSE SHOWING TRACES OF THE
SEGMENTS (_Porcellio scaber_), AFTER ROULE.]
[Illustration: FIG. 34.--AN EMBRYO WOODLOUSE READY TO BE HATCHED
(_Porcellio scaber_), AFTER ROULE.]
In the last stages of the development the appendages become larger
still, the _heart_ makes its appearance, segmentation of the body is
completed, and except that the seventh pair of walking legs are as yet
rudimentary the woodlouse is completed. It is only after hatching that
the pair of legs mentioned, attain to their normal length.
The process of segmentation of the egg and the formation of its layers
lasts about a fortnight, while the completion of the development
proceeds much more rapidly, for another three weeks bring it to an end.
After the first moult or change of skin the last pair of walking
legs makes its appearance, and Mr. James B. Casserley [whose work
one of us (75) has described elsewhere] found when keeping a number
of the common pill-woodlouse (_Armadillidium vulgare_) in captivity
that his specimens did not subsequently change their skins more than
once in the six months during which he had them under observation. He
also noted that the crustaceans go on growing after they are sexually
mature. As his specimens grew older, Mr. Casserley noticed that their
colour became darker, and a curious point recorded by him is that two
examples of the same age may change their skins at the same time,
and while one may have afterwards nearly twice as many markings, on
the other very few at all will be seen. The time required for the
growth of a woodlouse from the size of a pin's head to that of an
adult example--say three-quarters-of-an-inch long--must be fairly
considerable, taking into account the fact that any appreciable
increase in size can only occur at a moult and Mr. Casserley's
observations as to the infrequency of the process in _Armadillidium
vulgare_. (See p. 14.)
=Habits and Economic Considerations.=--The construction of the
breathing organs of woodlice, and the necessity which exists for these
to be kept moist, restricts the habitats of the animals considerably.
Woodlice are found under stones and logs, beneath the bark of dead and
rotten trees, among decaying vegetable matter as well as living grass
and moss in damp or wet situations. When looking for some of the common
species under the bark of fallen trees it is surprising to notice that
the crustaceans may be entirely absent from many trunks, while when
another is examined which seems to differ very slightly, if at all, in
condition or situation, they are found in swarms. There is no doubt
but that the habits of woodlice would well repay the attention of
naturalists, who are now recognizing that besides anatomy as such, and
the classification which a knowledge of structure permits, there is the
equally important consideration of the creatures as they live their own
life and affect that of others. It is not our object to give a detailed
account of the ecology of British woodlice, but rather to provide a
basis from which it may be approached. Nevertheless a few general
remarks may not come amiss. Many points in the life-history of woodlice
may no doubt be learned by keeping them in captivity and there is just
sufficient difficulty in doing this successfully to give an interest to
the matter.
Apart from a supply of proper food, we take it that the chief object to
be attained is the provision of the amount of moisture required by the
particular species under examination, together with a sufficient supply
of air.
A great many interesting observations can be thus carried out, such
as those of Mr. Casserley, to which allusion has already been made.
The process of moulting for instance is well worth watching, and
although specimens with half their coat changed may be found in remote
corners, yet the whole course of the moult can be seen much better
in the case of captive woodlice. The following account is taken from
Mr. Casserley's description (75) of what happens in the case of
_Armadillidium vulgare_:--The approach of the moult is indicated by
the appearance of a white border on each segment of the body, which
becomes gradually more marked, while at the same time the animal is
seen to be less active and often makes a small burrow in which to
hide. Sometimes a sheltered corner against a stone is looked upon as
affording sufficient protection, but in either case each woodlouse
keeps to the place originally chosen. About ten days after the white
lines have become visible the animal appears to be divided into two.
Its skin is becoming loose and little movement can take place at the
joints of its body with the exception of that between the fourth and
fifth thoracic segments where the skin will ultimately break. The
woodlouse spends a day or two in this condition and then, by suddenly
walking forward, frees itself from the covering of the hinder portion
of its body. The three last pairs of walking legs are carefully pulled
out from the old skin, which now appears perfectly white, and at the
same time the lining of the hind portion of the alimentary canal (hind
gut) is also shed. After putting the tender half of his body well into
his corner or burrow the woodlouse proceeds to eat the part of his skin
that he has cast. The creature has now a very odd appearance. His front
half with the exception of the white edges is as it was before, the
rest of him instead of a light slaty blue, and is very soft as well as
proportionately a little larger.
In three days or so the tail end becomes hard and attains the normal
colour. Then the old skin from the front half is pushed off and the
creature becomes practically defenceless, so much so in fact, that any
of his species that happen to find him will attack him and eat all his
front half, rejecting, however, his now hardened tail-end.
Provided that the moulting woodlouse has survived (and in captivity, to
ensure this, he must be isolated), after three days his jaws will be
sufficiently hardened to allow of his eating, and usually he first of
all devours the second half of his cast skin. The operation of moulting
does not occupy quite so long a time in the case of young examples.
Specimens half-an-inch long do not moult more than once in six months
and show but little increase in size after the process.
Woodlice do not appear to live on either animal or vegetable food
alone, but adopt a mixed diet. It is, however, owing to their attacks
upon cultivated plants that the creatures are looked upon as pests by
the horticulturalist. The animals feed either in the night or in the
very early morning, on seedlings, orchid tubers, mushrooms, or anything
that comes to hand. Few of the accounts, however, of their ravages,
mention that the crustaceans have been caught absolutely in the act
of doing the damage ascribed to them. Some careful inquiries have
nevertheless enabled us to discover several observers who have watched
woodlice feeding. Mr. F. V. Theobald, of Wye College, and one of the
students at Swanley Horticultural College are among the number. The
former has also given us an account of the methods, out of many tried,
which he has found most successful for getting rid of the crustaceans.
Out of doors trapping with moss, sacking or horse-dung is best. In
glass houses, fumigation with hydro-cyanic acid gas has cleared them
out, and poison baits, especially potatoes cut and soaked in white
arsenic, have done some good. Stable manure is especially favourable to
these creatures, particularly when it is used "long": in this condition
it should therefore be avoided.
It is interesting to note how the woodlice in winter simply remain
where they happen to be so long as there is sufficient moisture, though
they are ready to run about as rapidly, for a time, as in summer,
should they happen to be disturbed.
No doubt many points of inter-relation between woodlice and other
animals remain to be discovered. Mr. John W. Odell tells us that on
Exmoor, in the open, he found no _Armadillidia_, though other forms
occurred under nine out of every ten stones that he turned over, and
here the smaller species of ants also abounded. Close to stone walls
_Armadillidia_ were to be seen to the exclusion of all other genera,
and this state of affairs was ascribed by Mr. Odell to the presence of
swarms of the large wood-ants which he considers would make short work
of any woodlice that could not protect themselves by rolling up.
We ought not to conclude this account without mentioning the fact that
woodlice once played an important part in medicine.
Doctor Fernie (28) gives some interesting extracts with regard to the
hog-louse and the woodlouse. The latter he seems to have identified
quite correctly as _Oniscus asellus_. He calls the former, however,
indiscriminately, "the common armadillo" (which is the old name for
the pill-woodlice now known as _Armadillidium_), "the pill millipede"
and "_Glomeris marginata_." The last two names are those of another
creature, not a crustacean, which when it is rolled up can be very
easily mistaken for an _Armadillidium_, though, when it uncurls, it
will be seen to have many more than seven pairs of legs. The local
appellations applied to the hog-louse by Doctor Fernie, and his remarks
with regard to its commonness, tend to show that it is _Armadillidium
vulgare_, to which he really refers, and the use of which in medicine
was commonly general.
Hog-lice were prescribed for scrofulous diseases and obstructions of
the liver and digestive organs, among other things, and the London
College of Physicians directed that the creatures should be prepared
by suspending them in a thin canvas bag placed within a covered vessel
over the steam of hot spirit or wine, so that being killed by the
spirit they might become friable. Hog-lice and Woodlice were also
administered alive, while the former were also put down the throats of
cows "to promote the restoration" of their cud, hence their name of
"cud-worm." There seems to be considerable evidence that even in modern
times Woodlice have had considerable remedial effect which depends upon
"an alkalescent fluid" contained in them.
=Local Names.=--Among the local names by which these creatures are
known are those of "sow bug," "lucre pig" (Berkshire), "carpenter"
and "chiselhog" (Berkshire). Doctor Fernie (28) gives a number of
others:--"thrush-louse," "tiggyhog," "cheslip," "kitchenball,"
"chiselbob," "lugdor," "palmer," and "cudworm." In the eastern
counties the same writer notes that they are known as "old-sows" or
"St. Anthony's hogs" while the Welsh call them "little grey-hogs," "the
little old women of the wood" or "grammar-sows," grammar signifying
a shrivelled up old dame. _Oniscus asellus_ was sometimes called
"socchetre," "church louse," and "chinch."
=Methods of Collection and Preservation.=--Woodlice should be collected
straightway into tubes or bottles half filled with 30 per cent.
methylated spirit.[3] Woodlice dropped into this weak spirit become
gradually narcotised and die, and they remain limp enough for purposes
of examination or to allow, of their legs and antennæ being set out
during the process of mounting. Specimens to be kept permanently should
be placed in 70 per cent. alcohol. For storage purposes the specimens
of each species from a given locality should be put together into a
small flat bottomed tube such as is used for pillules by apothecaries
or specially made for natural history purposes. A paper label on
which the name, locality, date of capture and any other necessary
particulars have been written with dark lead pencil, is not affected by
the spirit. The tubes may be corked, though if not frequently examined
all the spirit may evaporate, and cause the specimens to be spoilt. A
safer method is to plug the tubes with cotton wool and keep all those
containing a given species or specimens from a particular locality
beneath the surface of spirit in a large wide-mouthed bottle, into
which first of all some cotton wool has been put to prevent the tubes
from coming into sudden contact with the glass at the bottom. For show
purposes in museums, specimens taken direct from 30 per cent. spirit
should be mounted on slips of opal glass by means of gum-tragacanth
which has been powdered and shaken up in spirit before having water
added to it. The slips can be exhibited in glass tubes, six inches high
by one across, or in narrow stoppered museum jars. A variation of the
method is to mount the animals on clear glass and to place behind them
another strip of any colour that may be preferred.
=Classification.=--The various genera of woodlice are connected
together so closely, by intermediate forms, that their division into
families is, to a very great extent, arbitrary. Bate and Westwood
described but a single family Oniscidæ (I), though they distinguished
two sub-families:--Ligiinæ, which included the forms with many joints
to the flagellum of the antenna, and Oniscinæ, which contained the rest.
Since then the pill-woodlice have been thought by some to be
sufficiently different from the other genera to warrant their
separation, and three families namely, Ligiidæ, Oniscidæ, and
Armadillidæ have been recognized, as for instance by Dr. Scharff (63).
A fourth family--Trichoniscidæ--has been added by Professor G. O. Sars,
who in his _Crustacea of Norway_ (59) alludes to the division of the
tribe into the sections Ligiæ and Onisci and has adopted the following
classification:--
_Order_--=ISOPODA.=
_Tribe_--ONISCOIDA.
_Family I._--LIGIIDAE.
_Ligia._
_Ligidium._
_Family II._--TRICHONISCIDÆ.
_Trichoniscus._
_Trichoniscoides._
_Haplophthalmus._
_Family III._--ONISCIDÆ.
_Oniscus._
_Philoscia._
_Platyarthrus._
_Porcellio._
_Metoponorthus._
_Cylisticus._
_Family IV._--ARMADILLIDIIÆ.
_Armadillidium._
All the genera described by Professor Sars are represented in the
British Islands.
* * * * *
Below is a scheme of classification and synopsis of the characters of
British genera of woodlice which we have compiled in order to render
easy the determination of the genus to which any particular specimen
may belong.
_SCHEME OF CLASSIFICATION AND SYNOPSIS OF GENERIC CHARACTERS._
_Order_--=ISOPODA.=
_Tribe_--ONISCOIDA.
_Section I._--=LIGIÆ.=
_The Two Divisions of the Tail Appendages alike in Shape._
(A.)--Flagellum with 10 or more joints; tail
appendages wholly visible; head without
lateral lobes LIGIIDAE.
(1.)--Abdomen broad; body large;
habitat, the sea-shore _Ligia._
(2.)--Abdomen narrow; habitat, wet
moss _Ligidium._
(B.)--Flagellum with less than 10 joints; head
with small lateral lobes, tail appendages
partly covered TRICHONISCIDÆ.
(3.)--Abdomen narrow; eyes compound;
flagellum usually with more
than 3 joints _Trichoniscus._
(4.)--Abdomen narrow; eyes simple or
wanting; flagellum with 4 joints _Trichoniscoides._
(5.)--Abdomen broad (comparatively);
eyes simple; back with
longitudinal ridges; flagellum
with 3 joints _Haplophthalmus._
_Section II._--=ONISCI.=
_The Outer Divisions of the Tail Appendages Broader than the Inner._
(A.)--Tail appendages projecting when the animal
is walking ONISCIDÆ.
(a.)--Unable to roll up into a complete ball.
(6.)--Flagellum with 3 joints; abdomen
broad; head, with lateral lobes _Oniscus._
(7.)--Flagellum with 3 joints; abdomen
narrow; head without lateral
lobes _Philoscia._
(8.)--Flagellum with 1 joint; eyes
wanting; abdomen broad; habitat,
ant's nests _Platyarthrus._
(9.)--Flagellum with 2 joints; abdomen
broad; frontal lobe projecting _Porcellio_.
(10.)--Flagellum with 2 joints; abdomen
narrow _Metoponorthus._
(b.)--Able to roll up into a complete ball.
(11.)--Flagellum with 2 joints; antennae
folded together over the thorax
when the animal is rolled up
into a ball _Cylisticus._
(B.)--Tail appendages not projecting when the
animal walking ARMADILLIDIIDÆ.
(12.)--Flagellum with 2 joints; antennae
hidden or carried at the sides
of the head when the animal is
rolled up into a ball _Armadillidium._
=British Species.=--Naturalists in this country paid little attention
to the recognition or description of Woodlice, until the latter half of
the nineteenth century.
In 1857 Kinahan read a paper before the British Association (32) in
which he described fourteen species of woodlice from the British
Islands, and eleven years later when Bate and Westwood published
their book (1), the number had risen to seventeen. One of the species
(_Oniscus fossor_), however, was doubtful, and although Dr. Scharff
in 1894 (63) rejected it, his list contained also seventeen species,
for in the meantime the Rev. T. R. R. Stebbing had found _Ligidium
hypnorum_ in Surrey (70).
Since then the Rev. Canon Norman, Dr. Scharff, the Rev. T. R. R.
Stebbing, and one of the present writers, have added other species, as
will be seen from the following pages, in which all those found, up to
the present time in the British Islands are described and figured.
We shall now consider in detail the British genera and species of
woodlice and give their synonymy and distribution.
_Order_--=ISOPODA.=
_Tribe--ONISCOIDA._
_Section_--=LIGIÆ.=
THE TWO DIVISIONS OF THE TAIL APPENDAGES ALIKE IN SHAPE.
_Family_--LIGIIDÆ.
=Flagellum with ten or more joints; tail appendages wholly visible;
head without lateral lobes.=
_Genus_--=LIGIA= Fabricius, 1798 (27), p. 301.
_Abdomen broad; body large; habitat, the sea-shore._
The genus _Ligia_ agrees with _Ligidium_ alone, in that the flagellum
of the larger antennæ has more than ten joints. In both genera, there
are no lateral lobes to the head, and the tail appendages are wholly
visible from the upper surface of the body. The latter in _Ligia_ is,
however, very many times bigger than in _Ligidium_ and shows no abrupt
decrease in the width of its segments when the abdomen is reached.
=Ligia oceanica= Linné (The Quay-louse). PLATE I.
1767 _Oniscus oceanicus_ Linné (43), p. 1061.
1793 _Cymothoa oceanica_ Fabricius (26), p. 509.
1815 _Ligia scopulorum_ Leach (38), p. 374.
1868 _Ligia oceanica_ Bate and Westwood (1), p. 444.
1898 _Ligia oceanica_ Sars (59), 156, pl. LXX.
There is but one British species of _Ligia_, and this, the largest
member of the whole tribe to be met with in these Islands, usually
attains a length of two centimetres, while adult males may be nearly
half as long again. It is the _Oniscus oceanicus_ of Linnæus and lives
on the sea shore, where it may be found at low tide beneath stones and
rubbish in the crevices of timber. _Ligia_ forms a connecting link
between the woodlice proper and the many Isopods which actually live in
the sea.
The colour of the animals is a greenish grey, and the compound eyes
are almost black, so that they are very conspicuous; there are from
eleven to fourteen joints to the flagellum of the outer antennae and
this feature, taken in conjunction with the large size and habitat, is
sufficient to identify the species in question.
On the coast of Essex the name "quay-lowders" is given to these
crustaceans, "lowder" being apparently an old plural of louse.
[Illustration: FIG. 35.--FLAGELLUM AND LAST PEDUNCULAR JOINT OF THE
ANTENNA OF _Ligia oceanica_.]
It is worthy of mention that Mr. Webb, when in charge of the Marine
Biological Station at Brightlingsea, examined a very large male
specimen of _Ligia oceanica_, in which the maxillæ were duplicated and
consisted of four pairs instead of two.
_BRITISH LOCALITIES:--_
_England_: Brightlingsea; (W.M.W.): Maldon; (W.M.W. from R.M.):
Southend; (J.A.M.): Whitstable; (W.M.W.): Herne Bay; Margate;
Dover; Folkestone; (J.A.M.)
_Scotland_: Shetland to Cornwall; (Norman, 49).
_Ireland_: East Coast; West Glengariff; Castletown; Berehaven;
Bundoran; (Scharff, 63).
_FOREIGN DISTRIBUTION:--_
_Europe_: France; (25): Spain; (12): Denmark; Prussia; Norway;
Faroe Islands; Belgium; (59).
_Africa_: Morocco; (16).
_Genus_--=LIGIDIUM= Brandt, 1833 (3), p. 173. Zia, Koch (34).
_Abdomen narrow; habitat, wet moss._
In _Ligidium_ there are numerous joints to the flagellum, lateral
lobes are absent from the head, and the tail appendages are completely
to be seen. All the segments of the abdomen are distinctly narrower
than those of the thorax and in this it agrees with _Trichoniscus_,
_Trichoniscoides_, _Philoscia_, and _Metoponorthus_. In these, however,
the flagellum has never more than seven joints, the tail appendages (as
in all genera but _Ligia_ and _Ligidium_) are partially hidden by the
last segment, and in all the four but _Philoscia_ there are lobes to
the head.
=Ligidium hypnorum=, Cuvier. PLATE II.
1792 _Oniscus hypnorum_ Cuvier (9), pl. XXVI., figs. 3-5.
1793 _Oniscus agilis_ Persoon, quoted by Koch in Panzer (51),
part 5, pl. XXIV.
1830 _Ligia hypnorum_ Bosc (2), p. 179.
1833 _Ligidium persoonii_ J. F. Brandt (3), p. 174, pl. IV.,
figs. 6-7.
1840 _Zia agilis_ Koch (34), part 34, pls. XXII. and XXIII.
1844 _Ligidium personii_ Zaddach (77), p. 17.
1853 _Ligidium personii_ Lereboullet (39), p. 14, pl. I., fig. 1,
pl. II., figs. 20-31.
1857 _Ligidium personii_ Kinahan (32), p. 275, pl. XXI., fig. 14,
pl. XXII., fig. 9.
1873 _Zia saundersii_ Stebbing (70), p. 286.
1873 _Ligidium agile_ Norman (48), p. 419.
1885 _Ligidium hypnorum_ Budde-Lund (8), p. 254.
1898 _Ligidium hypnorum_ G. O. Sars (59), p. 158, pl. LXXI.
This species, which like the last, is the only British representative
of its genus, was added to our fauna in 1873 by the Rev. Thomas R. R.
Stebbing (70) who found specimens in the neighbourhood of Copthorne
Common, Surrey. Up to the present time, when we are pleased to announce
that we discovered it in the spring of 1902 at Warley in Essex,
_Ligidium hypnorum_ has not been recorded from any other place in the
British Islands.
[Illustration: FIG. 36.--FLAGELLUM AND LAST PEDUNCULAR JOINT OF THE
ANTENNA OF _Ligidium hypnorum_.]
As the name of the species implies, it lives in wet situations and in
its turn connects _Ligia_ with the forms which inhabit drier places.
_Ligidium hypnorum_ might be mistaken for _Philoscia muscorum_, but as
already pointed out in the generic description, the latter has but a
few (three) joints to the flagellum, instead of from ten to thirteen.
From _Ligia_, the species under consideration is distinguished by its
small size, narrow abdomen, and habitat.
_BRITISH LOCALITIES:--_
_England_: Warley, Essex; (W.M.W.): Copthorne Common, Surrey;
(Stebbing, 70).
_FOREIGN DISTRIBUTION:--_
_Europe_: France; (25): Sweden; Denmark; Germany; (59): Turkey; (8).
_Family_--TRICHONISCIDÆ.
=Flagellum with less than ten joints; head with lateral lobes; tail
appendages partly hidden.=
_Genus_--=TRICHONISCUS= Brandt, 1833 (3), p. 174.
_Abdomen narrow; eyes compound; flagellum, usually with more than three
joints._
In _Trichoniscus_ the flagellum may have from seven to four (rarely
three) joints. As in _Trichoniscoides_ and _Haplophthalmus_ there are
lateral lobes to the head, though these are not very pronounced; the
body is also of small size, the abdomen narrow with both divisions of
the tail appendages equally so, and almost of the same length though
slightly covered by the last segment. The compound eyes distinguish
_Trichoniscus_ from the two genera named, and from _Platyarthrus_,
while its small size and the character of its tail-parts mark it out
from all others.
=Trichoniscus pusillus= Brandt. Plate III.
1833 _Trichoniscus pusillus_ Brandt (3), p. 174, pl. IV., fig. 9.
1838 _Itea riparia_ Koch (34), part 22, pl. XVII.
1844 _Itea lævis_ Zaddach (77), p. 16.
1857 _Philougria celer_ Kinahan (32), p. 281, pl. XXII., figs. 1-4.
1858 _Philougria riparia_ Kinahan (33), pp. 191 and 198, pl. XXIII.,
fig. 1.
1868 _Philougria riparia_ Bate and Westwood (1), p. 456.
1898 _Trichoniscus pusillus_ Sars (59), p. 161, pl. LXXII., fig. 1.
This tiny species is found commonly amongst the roots of the herbage in
very moist places. It presents a horny translucent appearance and is
of a reddish brown colour. It runs with considerable speed, and when
it is moving, the white irregular lines with which it is beset are
not evident. _Trichoniscus pusillus_ is very much like _Trichoniscus
vividus_ in colour but the latter species is nearly twice as big and
has from five to seven joints to the flagellum, while the former has
never more than four. _Trichoniscus roseus_ is also much larger and
its bright red colour (which it loses, however, when preserved in
alcohol) is another means of distinguishing it from the species under
consideration.
Professor Sars in his _Crustacea of Norway_ (p. 162) describes from
Christiania, under the name of _Trichoniscus pygmæus_, a still smaller
species. As this may possibly be discovered in this country a brief
comparison between it and _Trichoniscus pusillus_ may be of value.
The former reaches a length of but two millimetres; it is "whitish,
semi-pellucid with a few light brown pigmentary ramifications across
the segments and a double row of irregular opaque patches along the
middle of its back" (p. 163). Its body is covered with minute tubercles
and there are only three joints to the flagellum; its movements are by
no means rapid.
[Illustration: FIG. 37.--FLAGELLUM AND LAST PEDUNCULAR JOINT OF THE
ANTENNA OF _Trichoniscus pusillus_.]
The body of _Trichoniscus pusillus_ is smooth and polished. It has four
joints to the flagellum--Dr. Scharff (63) says three or four--and it
moves quickly.
_BRITISH LOCALITIES:--_
_England_: Brightlingsea; Warley; (W.M.W.): Epping Forest; (Bate
and Westwood, 1): Hanwell; Southall; Kew Gardens; Langley; Burnham
Beeches; Dropmore; Skirmett; Bluebell Hill, Maidstone; (W.M.W.):
Chislehurst; Plymouth; Polperro; Looe; (Bate and Westwood, 1):
Hertfordshire; Northumberland; Durham; (Norman, 49): Exeter;
(Parfitt, 53).
_Scotland_: Edinburgh; (Scott, 68): Cumbrae; (Robertson, 57).
_Ireland_: Connemara; (Norman, 49): Dublin; Wexford; Cork and
Kerry; (Percival Wright _teste_ Bate and Westwood, 1): Tyrone;
Waterford; Portlaw; Kilkenny; Wicklow; (Kinahan, 33).