Part 8
This is allied closely to _C. fasciatus_, and is best separated from that species by the shape and armature of the genital parts; the manubrium is not as long as in that species, and the bristles on the movable finger are shorter; the third joint of the maxillary palpi is proportionally longer than in _C. fasciatus_. There are three bristles in front of the eyes and four or five in front of these; there are a few hairs on the inner surface of the hind femur; the proportions of the joints in the hind tarsus are 46–30–18–11–18.
It has been recorded by Doctor Fox from _Mus rattus_ in California, and 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.