Other Arachnids--as mites, ticks, scorpions, daddy longlegs or
harvest-men--may be collected in the same way as spiders.
The Phalangidae (Harvest-men) somewhat resemble spiders, and are at once
recognized by their extremely long legs. They occur about houses,
especially in shady places, under the eaves, etc., and in the woods and
fields. They are carnivorous and feed on small insects, especially
Aphides. They should be pressed a little when captured to extrude the
genital apparatus, if possible, and are best collected in the early
fall.
[Illustration: FIG. 131.--A Harvest-man (_Phalangium
ventricosum_).--From Packard.]
The Phrynidae are very peculiar looking animals, the anterior legs being
very long and slender and the maxillary palpi very large. The genus
_Thelyphonus_ is not uncommon in the South, and is known by its oblong
body, ending usually with a long, slender, many-jointed filament, from
which they are called Whip-tailed Scorpions. _T. giganteus_ is the
common species. They occur in moist situations, and are carnivorous,
feeding on insects and small animals.
The false scorpions, Chermetidae, may at once be recognized by their
large maxillary palpi, resembling the maxillae of the true scorpion. They
are small insects, rarely exceeding a quarter of an inch in length, and
are found in dark shady places and feed upon mites, Psoci, and other
small insects. A common species is represented at figure 132.
[Illustration: FIG. 132.--False Scorpion (_Chelifer cancroides_
L.).--From Packard.]
The true scorpions, Scorpionidae, are well-known forms, and are easily
recognized by their large, powerful, forceps-like maxillae, and the long
slender tail continuous with the thorax and ending with a sting, which
is, in most cases, quite poisonous. They are found mostly in the Western
and Southwestern States, and are dangerous in proportion to their size.
The poisonous nature of the sting of these animals is, however,
generally overrated, and the wounds, even of the larger species, are
rarely fatal.
The Acarina or true mites are the lowest representatives of the
Arachnida and include many genera and species differing very widely in
habit and characters. Some of them are mere sacs, on which the mouth
parts or other organs are scarcely discernible. In general they resemble
spiders. The young, however, when they leave the egg, almost invariably
have but three pairs of feet, resembling in this respect the Hexapods.
The fourth pair is added in the later stages. They are parasitic on
insects and other animals, and some of them are vegetable feeders or
live in decaying vegetable and animal matter.
A very interesting group is comprised in the family Phytoptidae or
gall-making mites which occur on the leaves of various trees and shrubs
and produce curious galls or abnormal growths. These mites are elongate
in form, have rudimentary mouth-parts and but four legs. A common form,
_Phytoptus quadripes_, produces a gall on the leaves of the soft maple.
The galls of all species should be collected and pinned and also
preserved in alcohol, and specimens of the mites should be mounted in
balsam.
The members of the genus Sarcoptes are very minute and are the active
source of the itch in the lower animals and man. Another common genus is
Tyroglyphus, which includes the common cheese mite, _T. siro_. Other
species of this genus also sometimes occur in enormous numbers in
grocers' supplies. Still others are parasitic on insects, and one
species, _T. phylloxerae_ Riley, is very beneficial, since, as its name
indicates, it feeds on the Phylloxera of the grapevine.
[Illustration: FIG. 133.--A true Scorpion (_Buthus carolinianus_).--From
Packard.]
The Ixodidae comprise the ticks which attach themselves to cattle, hogs,
and man, and are not at all uncommon objects. These insects can be found
on the animals they infest, and distinct species will be found to occur
on most wild mammals. The common Cattle tick _Boophilus bovis_ Riley, is
represented at Fig. 134.
[Illustration: FIG. 134.--The Cattle-tick. (After Packard.)]
The family Orobatidae includes a number of small terrestrial mites, which
occur on the moss on trees and stones. Some species are known to feed on
the eggs of insects, and the one shown in the accompanying figure,
_Nothrus ovivorus_ has been observed, by Dr. Packard to eat the eggs of
the Canker Worm.
[Illustration: FIG. 135.--_Nothrus ovivorus_ Packard.]
The members of the family Gamasidae are parasitic upon animals, but
chiefly upon insects. The Hydrachnidae are parasitic also upon the
aquatic insects, and also affect fish or mussels or occur on fresh-water
plants.
One of the most important families of mites is the Trombidiidiae which
includes a large number of species, some of which occur in immense
numbers. Most of them are vegetable feeders, but some species feed on
the eggs of insects.
[Illustration: FIG. 136.--_Trombidium locustarum_: _a_, female with her
batch of eggs; _b_, newly hatched larva--natural size indicated by the
dot within the circle; _c_, egg; _d e_, vacated egg-shells.]
The genus Trombidium includes a number of the Red Mites which feed on
insects in all their stages. The Locust Mite, _Trombidium locustarum_
Riley, is one of the most interesting as well as one of the most
important of our locust enemies, and will serve to illustrate the habits
of the group. It differs so much in infancy and maturity that it has
been referred to different genera and is known under different names.
The mature form lives on the ground and feeds on all sorts of animal or
decomposing vegetable matter, and wherever the ground is filled with
locust eggs these afford an abundance of food and the mites flourish and
multiply rapidly. In the spring the female lays 300 or 400 minute
spherical orange-red eggs in the ground (Fig. 136_a_). From these eggs,
as shown enlarged at _c_, _d_, and _e_ (the two latter being the vacated
egg shells) emerge the six-legged larva shown at _b_. These are mere
specks and crawl actively about, fastening themselves to the locusts
mostly at the base of the wings or along the upper veins. They subsist
on the juices of their host. They firmly attach themselves by the mouth
and increase rapidly in size, the legs not growing and becoming mere
rudiments. In this form they are shown at Fig. 137_a_. When fully
developed they let go their hold, drop to the ground, and crawl under
the shelter afforded by holes in the earth or under sticks. Here, in the
course of two or three weeks, they transform within the larval skin to
the pupal stage shown at _b_, and eventually break through the old
larval skin and escape in the form shown at _c_ and _d_. This mature
form passes the winter in the ground and is active whenever the
temperature is a few degrees above the freezing point. A larger species
_T. giganteum_ Riley, also attacks locusts, while a third species
attacks the common House-fly. This was formerly known in the larva state
only and was referred to the genus Astoma, to which also the larval form
of Trombidium was referred. I have described the adult together with the
larva and pupa as _Trombidium muscarum_. An allied mite, _Hydrachna
belostomae_, attacks the large aquatic water bug, Belostoma, and has a
mode of development precisely similar to that of Trombidium.
[Illustration: FIG. 137.--_Trombidium locustarum_. _a_, mature larva
when about to leave the wing of a locust; _b_, pupa; _c_, male adult
when just from the pupa; _d_, female--the natural sizes indicated to the
right; _e_, palpal claw and thumb; _f_, pedal claw; _g_, one of the
barbed hairs; _h_, the striations on the larval skin.]
To this family also belong the common greenhouse mite, _Tetranychus
telarius_, and also the Bryobia mite, _B. pratensis_, which of late
years has attracted very considerable attention by its appearance in
immense numbers about dwellings, coming from the adjoining fields of
clover or grass. Generically allied to the greenhouse mite is the
Six-spotted Mite of the Orange (_T. 6-maculatus_ Riley), which is shown
in the accompanying figure.
[Illustration: FIG. 138.--The Six-spotted Mite of the Orange
(_Tetranychus 6-maculatus_): _a_, from above--enlarged; _b_, tarsus;
_c_, rostrum and palpus--still more enlarged; _d_, tip of palpus--still
more enlarged.]
Spiders and mites thus collected may be transferred to alcohol. Dr.
Marx, who has had a very considerable experience in the preservation of
spiders, recommends the use of the following mixture: Glycerin and
Wickersheim's fluid, 11/2 ounces of each, and distilled water 3 ounces,
the whole to be shaken and thoroughly mixed and added to 30 ounces of 95
per cent alcohol. Alcohol which has previously been used for preserving
spiders, and which has therefore dissolved some of the fatty matters
from the specimens, he prefers to pure alcohol, using with this,
however, somewhat less of the distilled water. The liquid thus composed
answers all demands and keeps the specimens flexible and preserves their
coloring. Should the stopper become loose and the liquid evaporate,
there is always sufficient liquid, water or glycerine, left in the vial
to keep the specimens from drying and thus save them from destruction.
Dr. Marx also prefers to use cork stoppers rather than the rubber
stoppers recommended for other alcoholic material. His objection to the
rubber stopper is that, in a collection in which the specimens are often
used and the stoppers are frequently removed, he finds that small
particles of the rubber stopper come off and settle upon the specimens
as a white dust, which it is difficult to remove. This objection applies
only to a poor quality of rubber, and in all other respects the rubber
is much to be preferred. The colors of spiders are apt to fade somewhat
if exposed to light, and the collection should therefore be kept in
closed boxes or in the dark.