HEXAPODA (Insects)
True insects have a single pair of antennæ, which is rarely vestigial, and usually one or two pairs of wings in the adult stage. Familiar examples are cockroaches, crickets, grasshoppers, bugs, dragon-flies, butterflies, moths, mosquitoes, flies, beetles, ants, bees and wasps.
ORDERS OF THE ARACHNIDA
a. Abdomen distinctly segmented. A group of orders including scorpions, ([fig. 11]), whip-scorpions ([fig. 10]), pseudo-scorpions, solpugids ([fig. 12]) harvest-men (daddy-long-legs or harvestmen), etc. Arthrogastra
aa. Abdomen unsegmented, though sometimes with numerous annulations Sphærogastra
b. A constriction between cephalothorax and abdomen ([fig. 7]). True Spiders Araneida
bb. No deep constriction between these parts.
c. Legs usually well developed, body more or less depressed ([fig. 49]). Mites Acarina
cc. Legs stumpy or absent, body more or less elongate or vermiform, or if shorter, the species is aquatic or semi-aquatic in habit.
d. Four pairs of short legs; species inhabiting moss or water. Water-bears. Tardigrada
dd. Two pairs of clasping organs near the mouth, instead of legs, in the adult; worm-like creatures parasitic within the nasal passages, lungs, etc. of mammals and reptiles ([fig. 148]). Tongue worms. Linguatulina
ACARINA[E]
a. Abdomen annulate, elongate; very minute forms, often with but four legs ([fig. 62]). Demodicoidea
b. With but four legs of five segments each. Living on plants, often forming galls. Eriophyidæ
bb. With eight legs, of three segments each. Living in the skin of mammals. Demodicidæ
To this family belongs the genus Demodex found in the sebaceous glands and hair follicles of various mammals, including man. D. phylloides Csokor has been found in Canada on swine, causing white tubercles on the skin. D. bovis Stiles has been reported from the United States on cattle, upon the skin of which they form swellings. D. folliculorum Simon is the species found on man. See [page 78].
aa. Abdomen not annulate nor prolonged behind; eight legs in the adult stage.
b. With a distinct spiracle upon a stigmal plate on each side of the body (usually ventral) above the third or fourth coxæ or a little behind ([fig. 50]); palpi free; skin often coriaceous or leathery; tarsi often with a sucker.
c. Hypostome large ([fig. 50]), furnished below with many recurved teeth; venter with furrows, skin leathery; large forms, usually parasitic. Ixodoidea
d. Without scutum but covered by a more or less uniform leathery integument; festoons absent; coxæ unarmed, tarsi without ventral spurs; pulvilli absent or vestigial in the adults; palpi cylindrical; sexual dimorphism slight. Argasidæ
e. Body flattened, oval or rounded, with a distinct flattened margin differing in structure from the general integument; this margin gives the body a sharp edge which is not entirely obliterated even when the tick is full fed. Capitulum (in adults and nymphs) entirely invisible dorsally, distant in the adult by about its own length from the anterior border. Eyes absent. Argus Latr.
f. Body oblong; margin with quadrangular cells; anterior tibiæ and metatarsi each about three times as long as broad. On poultry, southwest United States. A. persicus miniatus
A. brevipes Banks, a species with proportionately shorter legs has been recorded from Arizona.
ff. With another combination of characters. About six other species of Argas from various parts of the world, parasitic on birds and mammals.
ee. Body flattened when unfed, but usually becoming very convex on distention; anterior end more or less pointed and hoodlike; margin thick and not clearly defined, similar in structure to the rest of the integument and generally disappearing on distention; capitulum subterminal, its anterior portions often visible dorsally in the adult; eyes present in some species.
f. Integument pitted, without rounded tubercles; body provided with many short stiff bristles; eyes absent. On horses, cattle and man ([fig. 48]). Otiobius Banks.
O. megnini, a widely distributed species, is the type of this genus.
ff. Integument with rounded tubercles or granules; body without stiff bristles. Ornithodoros Koch.
g. Two pairs of eyes; tarsi IV with a prominent subterminal spur above; leg I strongly roughened. On cattle and man. O. coriaceus
gg. No eyes; no such spur on the hind tarsi.
h. Tarsi I without humps above. O. talaje.
hh. Tarsi I with humps above.
i. Tarsi IV without distinct humps above. On hogs, cattle and man. O. turicata
ii. Tarsi IV with humps nearly equidistant ([fig. 142]). Africa. O. moubata
dd. With scutum or shield ([fig. 50]); festoons usually present; coxæ usually armed with spurs, tarsi generally with one or two ventral spurs; pulvilli present in the adults; sexual dimorphism pronounced. Ixodidæ
e. With anal grooves surrounding anus in front; inornate; without eyes; no posterior marginal festoons; venter of the male with non-salient plates. Numerous species, 14 from the United States, among them I. ricinus (fig. [49] and [50]), scapularis, cookei, hexagonus, bicornis. Ixodes Latr. (including Ceratixodes).
ee. With anal groove contouring anus behind, or groove faint or obsolete.
f. With short palpi ([fig. 149]).
g. Without eyes, inornate, with posterior marginal festoons; male without ventral plates. Numerous species. H. chordeilis and leporis-palustris from the United States. Hæmaphysalis Koch.
gg. With eyes.
h. Anal groove distinct; posterior marginal festoons present.
i. Base of the capitulum ([fig. 150c]) rectangular dorsally; usually ornate. Dermacentor Koch.
j. Adults with four longitudinal rows of large denticles on each half of hypostome; stigmal plate nearly circular, without dorso-lateral prolongation, goblets very large, attaining 43µ to 115µ in diameter; not over 40 per plate, each plate surrounded by an elevated row of regularly arranged supporting cells; white rust wanting; base of capitulum distinctly broader than long, its postero-lateral angles prolonged slightly, if at all; coxæ T with short spurs; trochanter I with small dorso-terminal blade. Texas, Arizona, etc. D. nitens
jj. Adults with three longitudinal rows of large denticles on each half of hypostome; goblet cells always more than 40 per plate; whitish rust usually present.
k. Dorso-lateral prolongation of stigmal plate small or absent; plates of the adults distinctly longer than broad; goblet cells large, usually 30µ to 85µ in diameter, appearing as very coarse punctations on untreated specimens, but on specimens treated with caustic potash they appear very distinct in outline; base of capitulum distinctly (usually about twice) broader than long, the postero-lateral angles distinctly produced caudad; spurs of coxæ I long, lateral spur slightly longer than median; trochanter I with dorso-terminal spur. D. albipictus, (= variegatus), salmoni, nigrolineatus.
kk. Dorso-lateral prolongation of stigmal plate distinct.
l. Body of plate distinctly longer than broad; goblet cells of medium size, usually 17.5µ to 35µ or 40µ in diameter, appearing as medium sized punctuations on untreated specimens, but on the specimens treated with caustic potash they appear very distinct in outline, which is not circular; base of capitulum usually less than twice as broad as long, the postero-lateral angles always distinctly prolonged caudad.
m. Trochanter I with distinct dorso-subterminal retrograde sharp, digitate spur; postero-lateral angles of capitulum pronouncedly prolonged caudal, 112µ to 160µ long; goblet cells attain 13µ to 40µ in diameter; type locality California. D. occidentalis
mm. Trochanter I with dorso-terminal blade; postero-lateral angles of capitulum with rather short prolongations.
n. Stigmal plate small, goblet cells not exceeding 45 in the male or 100 in the female; scutum with little rust, coxa I with short spurs, the inner distinctly shorter than the outer. D. parumapertus-marginatus
nn. Stigmal plate larger; goblet cells over 70 in the male and over 100 in the female; coxa I with longer spurs, inner slightly shorter than the outer; scutum with considerable rust. D. venustus[F]
ll. Goblet cells small, rarely exceeding 17.6µ, occasionally reaching 19µ in diameter; on untreated specimens they appear as very fine granulations, and on specimens treated with caustic potash they may be difficult to see, but their large number can be determined from the prominent stems of the goblets; surface of outline of the goblets distinctly circular; base of the capitulum usually less than twice as broad as long, the postero-lateral angle distinctly prolonged caudad; spurs of coxæ I long. D. reticulatus and electus (= variabilis?)
ii. Base of the capitulum ([fig. 151]) usually hexagonal (except in the male of puchellus); and usually inornate.
j. No ventral plate or shield in either sex ([fig. 153]). R. bicornis from the United States. Rhipicentor Nuttall
jj. Males with a pair of adanal shields, and usually a pair of accessory adanal shields. Numerous species, among them R. sanguineus ([fig. 154]) and texanus, the latter from the United States. Rhipicephalus Koch
hh. Anal grooves faint or obsolete; no marginal festoons.
i. Short palpi; highly chitinized; unfed adults of large size; coxæ conical; male with a median plate prolonged in two long spines projecting caudad; segments of leg pair IV greatly swollen (fig. [155], [156]). M. winthemi Margaropus Karsch
ii. Very short palpi, ridged dorsally and laterally; slightly chitinized; unfed adults of smaller size; coxæ I bifid; male with adanal and accessory adanal shields ([fig. 139]). B. annulatus. Boophilus Curtis
ff. Palpi longer than broad ([fig. 157]).
g. Male with pair of adanal shields, and two posterior abdominal protrusions capped by chitinized points; festoons present or absent. Several species, among them H. ægypticum ([fig. 140]) from the old world. Hyalomma Koch
gg. Male without adanal shields but small ventral plaques are occasionally present close to the festoons. Many species, a few from the United States ([fig. 157]). Amblyomma Koch
h. Coxa I with but one spine, metatarsi (except I) with two thickened spurs at tips. A. maculatum
hh. Coxa I with two spines; metatarsi without stout spurs at tips, only slender hairs.
i. Projections of coxa I blunt and short. Large species on the gopher tortoise in Florida. A. tuberculatum
ii. Projections of coxa I longer, and at least one of them sharp pointed; second segment of palpus twice as long as the third; coxa IV of the male with a long spine.
j. Porose areas nearly circular; shield of both sexes pale yellowish, with some silvery streaks and marks, and some reddish spots; shield of female as broad as long. A. cajennense (= mixtum).
jj. Porose areas elongate, shield brown, in the female with an apical silvery mark, in the male with two small and two or four other silvery spots; shield of the female longer than broad ([fig 158 e]). A. americanum.
cc. Hypostome small, without teeth, venter without furrows; body often with coriaceous shields, posterior margin of the body never crenulate (i.e. without festoons); no eyes. GAMASOIDEA.
d. Parasitic on vertebrates; mandibles fitted for piercing; body sometimes constricted. Dermanyssidæ.
e. Anal plate present. Dermanyssinæ.
f. Body short; legs stout, hind pair reaching much beyond the tip of the body. On bats. Pteroptus Dufour.
ff. Body long; hind legs not reaching beyond the tip of the body.
g. Peritreme on the dorsum, very short; body distinctly constricted. Ptilonyssus Berl.
gg. Peritreme on the venter, longer; body not distinctly constricted.
h. Mandibles in both sexes chelate. Parasitic on bats, mice and birds ([fig. 150, h]). Liponyssus Kol.
The species L. (= Leiognathus) sylviarum frequents the nests of warblers. An instance is on record of these mites attacking man, causing a pruritis.
hh. Mandibles in the male chelate ([fig. 158 j]), in the female long, styliform. Parasitic on birds. Dermanyssus Dug.
Two species of importance may be noted, D. hirundinus and D. gallinæ. The latter ([fig. 51]) is a serious pest of poultry, sometimes attacking man, causing itching and soreness.
ee. Anal plate absent. In lungs and air passages of some mammals. Halarachninæ.
dd. Free or attached to insects, rarely on vertebrates.
e. First pair of legs inserted within the same body opening as the oral tube; genital apertures surrounded by the sternum. On insects. Uropodidæ.
ee. First pair of legs inserted at one side of the mouth opening; male genital aperture usually on the anterior margin of the sternal plate. Gamasidæ.
This family contains a number of genera, some of which are found upon mammals, though the majority affect only other arthropods. One species, Lælaps stabularis, frequents the bedding in stables, and in one instance at least, has occasioned irritation and itching, in man.
bb. No distinct spiracle in the stigmal plate on each side of the body.
c. Body usually coriaceous, with few hairs, with a specialized seta arising from a pore near each posterior corner of the cephalothorax; no eyes; mouth parts and palpi very small; ventral openings of the abdomen large; tarsi without sucker. Not parasitic. ORIBATOIDEA.
cc. Body softer; without such specialized seta.
d. Aquatic species. HYDRACHNOIDEA.
e. Palpi small, three segmented, adhering for some distance to the lip; ventral suckers at genital opening or near anal opening usually present; no eyes; tarsi often end in suckers; beneath the skin on the venter are seen rod-like epimera that support the legs; body often entire. Adults frequently parasitic. SARCOPTOIDEA.
f. With tracheæ; no ventral suckers; legs ending in claws; body divided into cephalothorax and abdomen; the female with a clavate hair between legs I and II. Usually not parasitic on birds and mammals. Tarsonemidæ
g. Hind legs of female ending in claw and sucker as in the other pairs. Pediculoidinæ
To this sub-family belongs the genus Pediculoides
P. ventricosus is described on [page 69].
gg. Hind legs of the female end in long hairs. Tarsoneminæ
Tarsonemus intectus Karpelles, normally found upon grain, is said to attack man in Hungary and Russia. Other species of the genus affect various plants (c.f. [fig. 150, g]).
ff. Without tracheæ; no such clavate hair.
g. Genital suckers usually present; integument usually without fine parallel lines.
h. Legs short, without clavate hair on tarsi I and II. On insects. Canestrinidæ.
hh. Legs longer, with a clavate hair on tarsi I and II. Not normally parasitic except on bees. Tyroglyphidæ
i. Dorsal integument more or less granulate; claws very weak, almost invisible; some hairs of the body plainly feathered; ventral apertures large. Glyciphagus Her.
This genus occurs in the United States. In Europe the mites have been found feeding on all sorts of substances. They are known as sugar mites and cause the disease known as grocer's itch. G. domesticus and G. prunorum are old world species ([fig. 150, d]).
ii. Dorsal integument not granulate; claws distinct; no prominent feathered hairs; ventral aperture small.
j. Mandibles not chelate; elongate, and toothed below; body without long hairs; palpi enlarged at tip and provided with two divergent bristles. Species feed on decaying substances. Histiostoma Kram.
jj. Mandibles chelate; palpi not enlarged at the tip, nor with two bristles.
k. No clavate hair on the base of tarsi I and II; no suture between cephalothorax and abdomen. Live on bees or in their nests. Trichotarsus Can.
kk. A clavate or thickened hair at the base of tarsi I and II.
l. The bristle on the penultimate segment of the legs arises from near the middle; no suture between the cephalothorax and abdomen. The species, some of which occur in the United States, feed on dried fruit, etc. Carpoglyphus Robin.
ll. The bristle on the penultimate segment of the legs arise from near the tip; a suture between cephalothorax and abdomen.
m. Cephalothorax with four distinct and long bristles in a transverse row; tarsi I and II about twice as long as the preceding segment ([fig. 150 f]). Tyroglyphus Latr.
n. Some bristles on tarsi I and II near middle, distinctly spine-like; the sense hair about its length from the base of the segment. Several species in the United States belong to this group.
nn. No spine-like bristles near the middle of the tarsi; sense hair not its length from the base of the segment.
o. Of the terminal abdominal bristles, only two are about as long as the abdomen; leg I of the male greatly thickened and with a spine at apex of the femur below. T. farinæ.
oo. Of the terminal abdominal bristles at least six or more are very long, nearly as long as the body.
p. Bristles of the body distinctly plumose or pectinate; tarsi very long. T. longior.
pp. Bristles of the body not pectinate.
q. In mills, stored foods, grains, etc. Third and fourth joints of hind legs scarcely twice as long as broad; abdominal bristles not unusually long; legs I and II of the male not unusually stout. T. americanus.
qq. With other characters and habits. T. lintneri ([fig. 150] f) the mushroom mite, and several other species.
mm. Cephalothorax with but two long distinct bristles (besides the frontal pair), but sometimes a very minute intermediate pair; tarsi I and II unusually short and not twice as long as the preceding segment.
n. Tarsi with some stout spines. Rhizoglyphus Clap.
The species of this genus are vegetable feeders. Several occur in the United States. R. parasiticus and R. spinitarsus have been recorded from the old world, attacking human beings who handle affected plants.
nn. Tarsi with only fine hairs. Monieziella Berl.
The species of this genus, as far as known, are predaceous or feed on recently killed animal matter. Several species occur in the United States. M. (= Histiogaster) entomophaga ([fig. 152]) from the old world has been recorded as injurious to man.
gg. Genital suckers absent; integument with fine parallel lines. Parasitic on birds and mammals.
h. Possessing a specially developed apparatus for clinging to hairs of mammals. Listrophoridæ.
hh. Without such apparatus.
i. Living on the plumage of birds. Analgesidæ.
ii. In the living tissues of birds and mammals.
j. Vulva longitudinal. In the skin and cellular tissues of birds. Cytoleichidæ.
This family contains two species, both occurring in the United States on the common fowl. Laminosioptes cysticola occurs on the skin and also bores into the subcutaneous tissue where it gives rise to a calcareous cyst. Cytoleichus nudus is most commonly found in the air passages and air cells.
jj. Vulva transverse. In the skin of mammals and birds Sarcoptidæ
k. Anal opening on the dorsum.
l. Third pair of legs in the male without apical suckers. On cats and rabbits. Notœdres Rail.
The itch mite of the cat, N. cati ([fig. 61]) has been recorded on man.
ll. Third leg in the male with suckers. On bats Prosopodectes Can.
kk. Anal opening below.
l. Pedicel of the suckers jointed; mandibles styliform and serrate near the tip. Psoroptes Gerv.
P. communis ovis is the cause of sheep scab.
ll. Pedicel of the suckers not jointed; mandibles chelate.
m. No suckers on the legs of the females; parasitic on birds, including chickens. C. mutans is itch mite of chickens. Cnemidocoptes Fürst.
mm. Suckers at least on legs I and II; parasitic on mammals.
n. Legs very short; in the male the hind pairs equal in size; body usually short. Sarcoptes Latr.
S. scabiei is the itch mite of man ([fig. 56]).
nn. Legs more slender; in the male the third pair is much larger than the fourth; body more elongate.
o. Female with suckers on the fourth pair of legs. Species do not burrow in the skin, but produce a scab similar to sheep scab. They occur in the ox, horse, sheep and goat. Chorioptes Gerv.
C. symbiotes bovis of the ox has been recorded a few times on man.
oo. Female without suckers to the fourth legs.
p. Hind part of the male abdomen with two lobes. On a few wild animals. Caparinia Can.
pp. Hind part of the male abdomen without lobes. Live in ears of dogs and cats. Otodectes Canestr.
O. cynotis Hering ([fig. 150 e]) has been taken in the United States.
ee. Palpi usually of four or five segments, free; rarely with ventral suckers near genital or anal openings; eyes often present; tarsi never end in suckers; body usually divided into cephalothorax and abdomen; rod-like epimera rarely visible; adults rarely parasitic.
f. Last segment of the palpi never forms a thumb to the preceding segment; palpi simple, or rarely formed to hold prey; body with but few hairs. EUPODOIDEA.
g. Palpi often geniculate, or else fitted for grasping prey; mandibles large and snout like; cephalothorax with four long bristles above, two in front, two behind; last segment of leg I longer than the preceding segment, often twice as long. Bdellidæ.
gg. Palpi never geniculate ([fig. 158a]), nor fitted for grasping prey: beak small; cephalothorax with bristles in different arrangement; last segment of leg I shorter or but little longer than the preceding joint; eyes when present near posterior border. Eupodidæ
Moniez has described a species from Belgium (Tydeus molestus) which attacks man. It is rose colored; eyeless; its legs are scarcely as long as its body, the hind femur is not thickened; the mandibles are small and the anal opening is on the venter. The female attains a length of about 0.3 mm.
ff. Last segment of the palpus forms a thumb to the preceding, which ends in a claw (with few exceptions); body often with many hairs ([fig. 158 k]). TROMBIDOIDEA.
g. Legs I and II with processes bearing spines; skin with several shields; coxæ contiguous. Cæculidæ.
gg. Legs I and II without such processes; few if any shields.
h. Palpi much thickened on the base, moving laterally, last joint often with two pectinate bristles; no eyes; legs I ending in several long hairs; adult sometimes parasitic. Cheyletidæ
Cheyletus eruditus, which frequents old books, has once been found in pus discharged from the ear of man.
hh. Palpi less thickened, moving vertically; eyes usually present; leg I not ending in long hairs.
i. Coxæ contiguous, radiate; legs slender, bristly; body with few hairs; no dorsal groove; tarsi not swollen. Erythræidæ.
ii. Coxæ more or less in two groups; legs less bristly.
j. Body with fewer, longer hairs; often spinning threads; no dorsal groove; tarsi never swollen; mandibles styliform (for piercing). Tetranychidæ
The genus Tetranychus may be distinguished from the other genera occurring in the United States by the following characters: No scale-like projections on the front of the cephalothorax; legs I as long or longer than the body; palp ends in a distinct thumb; the body is about 1.5 times as long as broad. T. molestissimus Weyenb. from South America, and T. telarius from Europe and America ordinarily infesting plants, are said also to molest man.
jj. Body with many fine hairs or short spines; not spinning threads; often with dorsal groove; tarsi often swollen.
k. Mandibles styliform for piercing. Rhycholophidæ.
kk. Mandibles chelate, for biting. Trombididæ
The genus Trombidium has recently been subdivided by Berlese into a number of smaller ones, of which some five or six occur in the United States. The mature mite is not parasitic but the larvæ which are very numerous in certain localities will cause intense itching, soreness, and even more serious complications. They burrow beneath the skin and produce inflamed spots. They have received the popular name of "red bug." The names Leptus americanus and L. irritans have been applied to them, although they are now known to be immature stages. ([Fig. 44].)
HEXAPODA (Insecta)
The Thysanura (springtails and bristletails), the Neuropteroids (may-flies, stone-flies, dragon-flies, caddis-flies, etc.), Mallophaga (bird lice), Physopoda (thrips), Orthoptera (grasshoppers, crickets, roaches), are of no special interest from our viewpoint. The remaining orders are briefly characterized below.
SIPHUNCULATA ([page 275])
Mouth parts suctorial; beak fleshy, not jointed; insect wingless; parasitic upon mammals. Metamorphosis incomplete. Lice.
HEMIPTERA ([page 275])
Mouth parts suctorial; beak or the sheath of the beak jointed; in the mature state usually with four wings. In external appearance the immature insect resembles the adult except that the immature form (i.e. nymph) never has wings, the successive instars during the process of growth, therefore, are quite similar; and the metamorphosis is thus incomplete. To this order belong the true bugs, the plant lice, leaf hoppers, frog hoppers, cicadas, etc.