is known from rats and mice from several parts of Europe; the _C.
italicus_ Tiraboschi is the same species.
The four other species of this genus found on rats and not yet found in
our country are closely related to _C. fasciatus_, and distinguished
chiefly by the shape of the male genitalia.
_Ceratophyllus mustelæ_ Wagner.
This species has no series of hairs on the inner surface of the hind
femur; there are three bristles in front of the eye and six in front of
these; the pronotal comb has 18 or 20 spines; the proportions of the
joints in the hind tarsus are 47–37–20–13–20; the movable finger of the
male clasper has a long process below not seen in other forms. Occurs
(according to Rothschild) on rats in Europe.
_Ceratophyllus pencilliger_ Grube.
This species also has no hairs on the inner surface of the hind femora.
The pronotal comb has 18 spines; there are three bristles in front of
the eye and four in front of these; the proportions of the joints in the
hind tarsus are 52–36–23–14–24; the outer corner of the movable finger
of the male clasper has two little rounded processes. It was described
from Siberia, but according to Rothschild occurs on rats in Europe.
_Ceratophyllus consimilis_ Wagner.
This species is very close to _C. fasciatus_, and has some fine hairs on
the inner surface of the hind femur; there are but two bristles in front
of the eye and in front of these a few finer hairs; the proportions of
the joints in the hind tarsus are 42–30–20–11–19; pronotal spines 18.
Occurs on rats in Russia.
_Ceratophyllus lagomys_ Wagner.
This species also has a few fine hairs on the inner surface of the hind
femur; 18 spines in pronotal comb; there are three bristles in front of
eye and one in front of these; the proportions of the joints in the hind
tarsus are 53–32–20–11–22; the outer corner of the movable finger of the
male clasper has two little processes, similar to those on _C.
pencilliger_. Occurs on rats in Europe.
_Ctenocephalus._—The common fleas on cats and dogs, as well as on man,
belong to two species long kept under one name (_C. canis_ or _C.
serraticeps_), but lately shown by Rothschild to be distinct. Both have
a comb of 8 spines on the head and 16 spines in pronotal comb; the
proportions of joints in the hind tarsus are 40–24–15–10–24. Both are
occasionally taken on rats in this country. They may be separated as
follows:
1. In the female the head is fully twice as long as
high (seen from side); the first spine of genal
comb is two-thirds the length of the second; in
male the manubrium of claspers is barely enlarged
at tip; and with two rows of hairs on disc of _C. felis_
movable finger Bouché.
In the female the head is less than twice as long
as high (seen from side); the first genal spine
in the head comb is only about one-half the
length of the second; in the male the manubrium
of clasper is very distinctly enlarged at tip;
but one row of hairs on the disc of the movable _C. canis_
finger Curtis.
_Neopsylla._—One species of this genus has been described from the brown
rat in Europe.
_Neopsylla bidentatiformis_ Wagner.
The eyes are very small; there are 4 pairs of lateral spines beneath the
last joint of the hind tarsus; the comb on head consists of but 2 stout
spines, below the middle of the antennæ; the pronotal comb has 18
spines; the proportions of the joints in the hind tarsus are
43–33–21–12–21.
Length: Male, 2 to 2.3 millimeters; female, 2.3 to 2.5 millimeters.
Not yet found in the United States; described from Russia.
SARCOPSYLLIDÆ.
The fleas of this family are commonly called “chigoes,” “jiggers,” or
sand fleas. The head is usually larger proportionally than in the other
fleas; there are no ctenidia on head or pronotum; the thoracic segments
are extremely short, and in the female the abdomen enlarges with the
development of the eggs. They do not hop about as other fleas, but
remain on the spot to which they have attached until they die.
Frequently the adjacent skin grows over them, forming a swelling of
considerable size.
Three species belonging to two genera have been recorded from rats.
1. Angle of head acutely produced; fifth tarsal joint
of hind legs without heavy spines; few spines on
the legs _Sarcopsylla_.
Angle of head not produced, obtuse; fifth tarsal
joint with heavy lateral spines, and other spines
on other parts of the legs _Echidnophaga_.
_Echidnophaga._—Two species of this genus are known from rats; one,
however (_E. gallinacea_), can hardly be called a normal parasite, but
rather of accidental occurrence. The genus has also been called
_Argiopsylla_ and _Xestopsylla_.
1. Bristles at end of second joint of hind tarsus
about as long as next three joints; palpi about _E.
one-half the length of mandibles rhynchopsylla_.
Bristles at end of second joint of hind tarsus
about as long as next two joints; palpi about
two-thirds the length of the mandibles _E. gallinacea_.
_Echidnophaga rhynchopsylla_ Tiraboschi.
The body is about twice as long as broad and shining brown; there is but
one hair in front of eye, and four on each metathoracic pleuron;
mandibles larger than in _E. gallinacea_, and the spiracles are much
higher up on the sides than in that species. Length, 1.4 to 1.8
millimeters.
Taken from _Mus rattus_ in Italy.
_Echidnophaga gallinacea_ Westwood.
This species has the body almost as broad as long, and of a red-brown
color; 1 bristle in front of eye and 6 on each metathoracic pleuron;
each abdominal tergite has on each side near the median line a single
hair; the spiracles are situated well down on the sides. Length: Male,
0.8 to 1.2 millimeters; female, 1 to 1.8 millimeters.
This species is a fairly common pest of poultry and dogs in warm
countries, and is called the “chicken flea.” It has been taken from rats
in Italy.
_Sarcopsylla._—This genus includes the _S. penetrans_, which attacks the
feet of various animals, including man, in the Tropics. This species has
not yet been recorded from rats, but an allied species is described from
Brazilian rats.
_Sarcopsylla cæcata_ Enderlein.
Color, clear yellowish. Eyes rudimentary; lower anterior corner of coxæ
prolonged in a tooth; tarsal joints very short; claws long, but little
curved, and almost hair like. The body of a swollen female is about 5
millimeters long.
Taken from _Mus rattus_ in Brazil.
LICE—ANOPLURA.
The insects known as Pediculi, or lice, are parasitic during their
entire life on various mammals, including man. They are flat, rather
elongate, wingless insects, with a small head and stout legs, which end
in a strong claw, opposable to a projection at the tip of the
penultimate joint. The simple antennæ, three to five jointed, are
inserted in a concavity on the side of the head. The mouth parts are of
a very peculiar nature, and not yet homologized with the cibaria of
other insects. There is a short beak or proboscis in front, with
recurved spines or hooks on its dorsal and lateral surfaces. Through
this beak extends a slender stylet, that is formed of three parts; a
ventral channeled piece, perhaps a labium; a dorsal piece, consisting of
two pieces fused together, perhaps the maxillæ; and a median tube,
possibly the hypopharynx. The stylet is used to pierce the skin of the
host, and the blood is sucked up through it. There are no palpi. On each
side of the head there is a small, simple eye. The thorax shows only
incompletely the division into the three parts; there is a large
spiracle above on each side. The abdomen shows eight segments, six of
them have a spiracle, or breathing pore, on each side, the basal and
apical segments being without them. All of the segments bear a few
simple hairs or bristles; the longest are on the posterior segments. The
legs are stout and prominent; they consist of a broad coxa, a small
trochanter, a longer femur, a tibia with an apical process, and a tarsus
of one joint and a very large terminal claw. At the apex of the tibia,
just within the projection, is a sucking disc. This, the projection, and
the claw form the apparatus to hold fast to the hair of the host.
Lice usually walk sideways, but do not travel much, and they keep close
to one host. The eggs are slightly elongate and fastened to the hair of
the host. They hatch in about ten to fifteen days, the young coming out
of the top of the egg. These young do not differ much in structure from
the adults, but are paler in color. They molt their skin a few times,
probably four, before they reach the mature condition. The males are
less numerous than the females, and ordinarily smaller. There are
several generations each year, dependent doubtless on the temperature;
but the life history is not thoroughly known for any species. After
sucking the blood the abdomen of the louse becomes somewhat distended,
very noticeably so in some species.
The sucking habits of the lice render them dangerous parasites and
capable of transmitting a disease from one host to another. Fortunately
they do not readily change hosts so that they can not be considered
quite as dangerous as some more active parasites. However, several
species have already been shown to carry diseases in laboratory
experiments. Therefore it is probable that some of them will be
connected with the origin and diffusion of certain diseases of animals.
[Illustration:
FIG. 7.—Louse (_Polyplax spinulosa_).
]
The Anoplura, or lice, have often been treated in connection with the
Mallophaga, or biting lice. This is doubtless because they frequently
occur on the same animal, and have a general resemblance to them.
However, they have no real affinity to these insects, and the general
opinion is that they are more or less related to the Hemiptera.
Sometimes they are treated as a group or section of the Hemiptera, but
also as a separate order, under various names as Siphunculata,
Lipognatha, Pseudorhynchota, and Ellipoptera.
There are about 50 or 60 known species which are arranged in 15 genera
and 4 families. Four species belonging to three different genera have
been recorded from rats; a number of others are known from mice and
other rodents, and some of these will probably yet be taken upon rats.
These four forms are separated, as follows:
1. Eyes large and distinct; beak very short; thorax _Pediculus
plainly longer than broad capitis_.
Eyes small, beak longer; thorax about as broad as
long 2
2. In male the pleura of abdominal segments 3 to 6
above and below have a prominent tooth-like _Hoplopleura
projection; a tooth on the hind femur of female acanthopus_.
In male the pleura of abdominal segments without
such projections; no tooth on hind femur of
female 3
3. Last joint of antennæ much more slender than those
before; an acute tooth at sides of segments 4 to
7; head much narrower in front; antennæ _Polyplax
two-thirds as long as head miacantha_.
Last joint of antennæ not much more slender than
others; head quite broad in front; antennæ as _Polyplax
long as head spinulosus_.
_Pediculus capitis_ De Geer.
It is pale grayish in color, with faint dark markings at the sides of
the thorax and abdomen; the last segment of the abdomen in female is
bilobed. The head is longer than broad and tapers in front. Length, 2
millimeters. This is the head louse of man, and is said to have been
taken from rats, and is claimed to be able to transfer plague from rats
to man. Its occurrence on rats, however, appears to be very uncommon.
_Hopopleura acanthopus_ Burmeister.
In the male the pleura of the abdominal segments 3 to 6, which reach up
on the dorsum and over on the venter, have at their inner ends a
prominent projection, toothed in all except the third on dorsum and the
sixth on venter, which are spine-like. The head is but little longer
than broad, broad in front; and in the female there is a recurved tooth
on each hind femur. The last segment of the female abdomen is bilobed
behind. Length, 1.3 millimeters. It has been taken from rats in Europe,
but is more common on species of _Microtus_.
_Polyplax spinulosus_ Burmeister.
The sides of the abdominal segments are acute, but the males do not have
the large tooth-like projection of _Hoplopleura_. The last segment of
the female is truncate; the head is about as broad in front as behind,
and the legs are very short and stout; the antennæ are as long as head,
and the last joint is but little smaller than the others. Color, pale
yellowish. Length, 1.4 millimeters.
This is the common rat louse, and is probably as widely distributed as
its host. Specimens have been taken in both the eastern and western
parts of the United States.
_Polyplax miacantha_ Speiser.
This differs from _P. spinulosus_ in having a longer and narrower
anterior part of head, in that the last joint of the antennæ is more
slender, and the antennæ are only two-thirds as long as the head. The
abdominal segments 4 to 7 show an acute process at the sides. Length,
1.5 to 1.75 millimeters.
Taken from rats in Abyssinia.
MITES—ACARINA.
The mites (order Acarina, class Arachnida) are readily known from the
insects (fleas and lice) by having four pairs of legs, no antennæ, and
the abdomen does not show any segmentation, nor is there usually any
distinction between head and thorax. In some groups there is a small
head-like part, called the capitulum. The mouth parts consist of a pair
of mandibles (often styliform or needle-like), a lip, and a pair of
palpi. In some forms there is a central piece, called the hypopharynx,
and in other groups is a plate above the mouth parts, known as the
epistome. The body usually shows more or less distinctly a division into
two parts—the anterior, called the cephalothorax, and the posterior the
abdomen. However, in many mites it is not possible to separate these
parts, except that it is considered that the legs are borne by the
cephalothorax. In many forms there is a small, simple eye each side on
the cephalothorax, but many other forms are blind. Some species have a
tracheal system, which opens in a pair of spiracles near the hind legs
or near the anterior end of the body; other species have no definite
respiratory system. The genital aperture is on the venter, usually
between the legs. The legs consist of the usual joints—coxa, trochanter,
femur, tibia, sometimes a metatarsus, and a tarsus. The tarsus
terminates in a pair of claws, sometimes three or only one, and often a
sucker or caroncle. Most mites are not parasitic; those species that are
parasitic are often free in one stage. The parasitic mites suck the
blood of their host, feed on the hair or dermal scales, or burrow in the
skin. Some predaceous species inhabit animals to hunt and eat the
parasitic mites that infest that animal.
The mites that occur parasitically on rats belong to four families:
Sarcoptidæ, Cheyletidæ, Ixodidæ, and Gamasidæ.
1. A distinct spiracle or breathing pore on each side
of body near coxæ III or IV 2
No such spiracle or pore visible 3
2. A small, distinct head part in front of the body;
palpi three jointed; a granulate area around the
spiracle; no sternal plate _Ixodidæ_.
No such head part; palpi five jointed; no granulate
space around spiracle, but a long, chitinized
piece reaching forward from it; a more or less
distinct sternal plate _Gamasidæ_.
3. All legs simple, unmodified, ending in a stalked
sucker _Sarcoptidæ_.
Front legs short, enlarged, and modified for
clasping; all legs end in one or two stout claws _Cheyletidæ_.
IXODIDÆ.
The Ixodidæ, or ticks, are rather large, flat, leathery-skinned mites,
which suck the blood of various animals. In the male the dorsum of the
body is nearly covered by a corneous shield, while in the female this
shield occupies only the anterior part of the body. In the female the
body swells to enormous proportions as she engorges herself on the blood
of the host. At the posterior margin of the body there are in many forms
a series of lobes or festoons. There is no species of tick that is
commonly found on rats, but four species that normally infest other
animals have been taken from them.
[Illustration:
FIG. 8.—Mite (_Lælaps echidninus_).
]
1. On the venter is a groove in front of the anus and
extending back each side; no festoons to _Ixodes
posterior margin of body; palpi rather long ricinus_.
On the venter there is no groove in front of the
anus, but usually one behind; festoons distinct
in males and unengorged females 2
2. Palpi very short with transverse ridges; shield of
female narrowed behind eyes; stigmal plate nearly _Margaropus
round annulatus_.
Palpi short, without transverse ridges; shield of
female not narrowed behind eyes; stigmal plate _Rhipicephalus
comma shaped sanguineus_.
Palpi elongate, without ridges; shield of female _Hyalomma
broad; stigmal plate oval, aegypticum_.
_Ixodes ricinus_ Linné.
The shield of the female is elliptical, plainly longer than broad, sides
not suddenly narrowed behind, and there is no eye-spot at each lateral
corner. The coxa I has a long sharp spine.
This is a common European tick found on sheep, cattle, dogs, etc., and
it has been taken a few times in this country. Neumann has recorded its
capture from _Mus decumans_.
_Margaropus annulatus_ Say.
The shield is plainly longer than broad, with a distinct eye-spot at
each lateral corner, and behind the eye the shield is suddenly narrowed;
the coxæ of the female are without spines, but the male has 2 on coxæ I.
This is the common cattle tick of the United States, and disseminates
the Texas fever. Mr. Hunter has taken it once from a rat in a barn at
Dallas, Tex.
_Rhipicephalus sanguineus_ Latreille.
The shield of the female is oval, and longer than broad, with an
eye-spot at each outer corner. Coxa I with 2 teeth; a smaller tooth on
each of the other coxæ. Stigmal plate long, comma shaped. In the male
there is a corneous plate each side of the anus, and on middle of
posterior margin a projection, or short tail.
This species is common in tropical countries, and Nuttall has recorded
specimens from the black rat in India.
_Hyalomma aegypticum_ Linné.
The shield of the female is as broad as long, and the eye-spot is
slightly above each outer corner. Coxa I has 2 large teeth, and a small
tooth on each of the other coxæ. In the male there are 2 corneous plates
each side of anus, and behind is a pair of small tubercles.
This is a common tick in the warmer parts of the Old World; and Nuttall
has recorded young specimens on the black rat.
GAMASIDÆ.
The Gamasid mites, although much smaller than the ticks, are large
enough to be seen by the naked eye. They are active, and most are not
parasitic, at least for part of their time. The palpi are simple, of 5
joints; the mandibles are elongate, retractile, and usually chelate at
tip. There are no eyes. The dorsum and often the venter shows one or
more corneous shields or plates, frequently a number of them; one or two
on the dorsum, and on the venter one between the coxæ, called the
sternal plate; one behind this, the genital plate; one behind the
latter, the ventral plate; and one surrounding the anus, the anal plate.
Frequently some of these are absent or united to one of the others.
The legs are slender, usually of 6 joints, with a long tarsus that
terminates in 2 claws, and often a sucker, or caroncle. The stigmata, or
spiracles, are lateral above and between coxæ II and IV, and usually
provided with a slender peritreme reaching forward toward the head.
Nearly all the Gamasidæ deposit eggs, and the young often differ
considerably from the adult in structure. There are two, and perhaps
sometimes three, nymphal stages. In one of these nymphal stages the mite
is apt to attach itself to an insect for the purpose of being carried to
a similar locality, where it may feed and mature. The coprophagous and
xylophagous insects are especially concerned in the diffusion of these
mites.
There are, however, quite a number of species that are genuine parasites
of insects and other animals. Those occurring on rats belong to two
genera, Myonyssus and Lælaps. They can be separated as follows:
1. Anal plate small, much smaller than the ventral
plate _Lælaps_.
Anal plate large, larger than the ventral plate _Myonyssus_.
_Myonyssus._—This genus is made by Tiraboschi for one species:
_Myonyssus decumani_ Tiraboschi.
Body oval; legs short and stout, all tarsi with a large caroncle with
two short claws; coxæ II have a large tooth on the anterior border, none
of coxæ with spines; sternal plate much broader than long, with three
bristles each side; ventro-genital plate much longer than broad,
broadest behind, bordered with bristles; anal plate very large, nearly
one and a half times as broad as long; three large spines each side on
venter. Length, 0.95 millimeter.
Found in Italy on _Mus decumans_.
_Lælaps._—This genus embraces a large number of species, several of
which occur on small animals, such as the muskrat, ground hog, and
chipmunk. Three have been recorded from rats, one of these from
California. The dorsal plate is covered with hairs or bristles, and
there are usually stout bristles on the margins of the plates on the
venter. There is also a bristle, or a spine, at the tip of the anal
plate. The legs are short and stout, with a distinct caroncle, and two
claws.
1. Dorsum with numerous fine hairs; no stout spines on
coxæ _L. stabularis_.
Dorsum with fewer, but stouter spine-like bristles;
each coxa has a stout spine 2
2. Body but little longer than broad; ventral plate
longer than broad _L. agilis_.
Body much longer than broad; ventral plate about as
broad as long _L. echidninus_.
_Lælaps echidninus_ Berlese.
Dorsum of body almost wholly covered with a shield, with rows (six in
front, eight behind) of stout, curved bristles, a longer pair near front
margin, and some around lateral and posterior margins. Legs short and
stout, tarsi about twice as long as preceding joint; each coxa bears a
stout spine near middle. Palpi very short; sternum with three stout
bristles or spines each side; ventral plate with four stout bristles
each side; anal plate with a stout apical bristle, and a small one each
side. Length, 1 millimeter.
Occurs commonly on rats in warm countries, and known from California. It
may possibly aid in the transmission of disease.
_Lælaps agilis_ Koch.
Similar in many respects to _L. echidninus_ but differ in the shorter
and proportionately broader body, barely longer than broad, and in the
weaker and shorter spines on dorsum and on the ventral plates; there are
also some small short spines on the general surface of the venter.
Length, 0.7 millimeter.
Recorded from rats from Europe and Africa.
_Lælaps stabularis_ Koch.
The body is of the same general shape as in _L. echidninus_, but the
dorsum is clothed with 12 to 18 rows of fine short hairs. The first pair
of legs is more slender than in the other species, and the hind legs are
also more elongate; the coxæ do not have the stout spines seen in the
other species, and the bristles on the sternal and ventral plates are
much less stout; the general surface of the venter has many hairs, the
anal plate has a short apical bristle. Length, 1.2 millimeters.
Taken on the brown rat in Italy; also found in manure.
CHEYLETIDÆ.
This family consists of small, soft-bodied mites, that are parasitic or
predaceous in habits. The palpi are small, three or four jointed; the
mandibles are styliform and retractile; and the breathing spiracles open
near the mouth parts. The species that occur on rats belong to the genus
_Myobia_.
_Myobia._—The body is elongate, fully twice as long as broad, tipped by
a pair of long, stout bristles. The first pair of legs is enlarged and
shortened, with a terminal hook to grasp hairs; the other legs are
short, simple, and far apart. The palpi and mouth parts are very small,
and the dorsum bears stout bristles. They are supposed to feed on the
exudations of the skin, but it would seem more probable, from the nature
of the mandibles, that they pierced the skin to secure food. All are
very small, not one-half a millimeter long. Of the several species two
have been recorded from rats.
1. Dorsum of female with spines all acute and sharp _M. musculi_.
Dorsum of female with some of the posterior spines
flattened and rather scale like _M. ensifera_.
_Myobia musculi_ Schrank.