Fam. 2. Argasidae.—The Argasidae are leathery Ticks without a shield or scutum, and with free, leg-like palps. The capitulum is never more than partially visible when the adult animal is viewed dorsally. Their hosts are always warm-blooded animals. Two genera are usually recognised, Argas and Ornithodoros, though recent discoveries of new forms have tended towards their fusion. Argas reflexus and A. persicus have been proved to convey a Spirochaete disease to fowls, and the latter, under the name of the “Mianeh Bug” has long possessed an evil reputation for the “poisonous” effect of its bite on human beings. In Mexico the “Turicata” (Ornithodoros turicata) and the “Garapata” (O. megnini) are greatly dreaded, while human “tick fever” on the Congo has been traced to the instrumentality of O. moubata.
Fig. [245].—Female Sheep-tick, Ixodes ricinus.
Fam. 3. Ixodidae.—These are the more familiar Ticks, possessing a scutum or shield, which covers the whole back of the male, which is capable, therefore, of little distension, whereas it forms only a small patch on the front part of the body of the distended female. There are ten genera, Ixodes, Haemaphysalis, Dermacentor, Rhipicentor, Rhipicephalus, Boophilus, Margaropus, Hyalomma, Amblyomma, and Aponomma.
Ixodes ricinus is the common English sheep-tick. Species of Boophilus are parasitic on cattle the world over, and B. annulatus is the transmitter of Texas fever. Rhipicephalus and Amblyomma are large genera which include several species of economic importance. For example, R. sanguineus conveys canine piroplasmosis, and A. hebraeum causes “heart-water” in South African cattle. The genus Aponomma confines its attention to reptiles, and some of its species are exceedingly ornate.
Neglecting Margaropus and Rhipicentor, which include only a very few aberrant forms, the following entirely artificial key will serve to differentiate the genera of the Ixodidae:—
| 1. | A pair of eyes on the lateral borders of the scutum | 2 |
| No eyes | 6 | |
| 2. | Capitulum long, much longer than broad | 3 |
| Capitulum short | 4 | |
| 3. | Unicolorous, ♂ with chitinous plates near anus | Hyalomma |
| Generally ornate, ♂ without anal plates | Amblyomma | |
| 4. | Generally ornate, ♂ without anal plates, but with enlarged 4th coxae | Dermacentor |
| Unicolorous, ♂ with anal plates and normal coxae | 5 | |
| 5. | Palpi very short, spiracle circular | Boophilus |
| Palpi medium, spiracle comma-shaped | Rhipicephalus | |
| 6. | Capitulum short; 2nd article of palp projecting laterally | Haemaphysalis |
| Capitulum long | 7 | |
| 7. | Unicolorous, elongate, on birds or mammals | Ixodes |
| Generally ornate, broad-oval, on reptiles | Aponomma |
Neumann has recently revised the Ixodoidea in a series of papers published in the Mémoires de la Société zoologique de France,[[370]] but the work is not obtainable as a whole. A monograph, by Nuttall, Warburton, Cooper, and Robinson, is now in course of publication at the Cambridge University Press.[[371]]
Fam. 4. Gamasidae.—The Gamasidae are carnivorous Mites, either free-living or parasitic on animals. The chelicerae are chelate, and the palps are free. The tarsi have two claws, accompanied by a “caruncle” or sucking disc. They are mostly pale-coloured Mites, with a smooth, more or less scutate covering. The three principal sub-families are Gamasinae, Uropodinae, and Dermanyssinae.
Of the Gamasinae, Gamasus coleoptratorum is the well-known Beetle-parasite so frequently seen on Geotrupes. It is often confounded with another species of similar habits, G. crassipes.