Measures 5 mm. in size; lives on birds in the Island of Mauritius; ducks and geese frequently fall victims to its bite; it also attacks human beings, on whose skin it causes severe burning and swelling, but no reddening; it may be dangerous to children, especially by settling in the oral cavity.
Other Gamasides occasionally occur in man, for instance, according to Moniez, Leignathus sylviarum, Canestr. et Fanzago; according to Neumann Lælaps stabularis. The former live normally in the nests of various species of Sylvia, Lælaps on dried vegetable substances, also in houses.
[Marchoux and Conoy (Bull. Soc. Path. exot., 1912, v, No. 10, pp. 796–798) found Leishman granules in Lælaps echidninus. It is assumed that Leishman granules may be found in most Arachnoids, and have no connection with Spirochæta.—F. V. T.]
Family. Ixodidæ (Ticks).
Comparatively large Acarines with a leathery skin; they are flattened in form, but after sucking blood the abdomen becomes spherical; the cheliceræ are rod-like and possess a serrated terminal joint, bent hook-like; the median parts of the pedipalpi (maxillæ) form a rostrum furnished with barbed hooks (fig. [359]); the maxillary palpi themselves are club-like or rounded; the legs are composed of six segments with two terminal ungues, often also with “sucking discs”; the stigmata are at the sides of the body, posterior to the fourth or third pair of legs. The larvæ are six-legged.
[The true ticks (Ixodidæ) are all blood-suckers, and as far as is known they do not take vegetable food at all. Not only are the Ixodidæ important as actual parasites, but they are most so on account of the fact that they are the active agents in carrying various diseases in animals and apparently in man. It has been conclusively proved that the bont tick (Amblyomma hebræum) is the carrier of the fatal “heart-water fever” so rife amongst sheep in South Africa, that the dog tick (Hæmaphysalis leachi) is the agent by which the protozoa that cause malignant jaundice in dogs are distributed, that Texas fever in cattle is spread by Rhipicephalus annulatus, and Coast or Rhodesian fever by R. appendiculatus and R. simus. Their importance as disease carriers amongst mammals is therefore considerable, and it may prove to be so for man.[336] They frequently attack man, but chiefly, according to my observations, in their early stages in Europe; this is not so, however, abroad. The life-history of a number of ticks has been clearly demonstrated. Mr. Wheler has shown that in Ixodes reduvius it is as follows: the female deposits her eggs in masses upon the ground, gradually reducing in size as the eggs pass out, until she finally remains a mere shrivelled empty bag and then dies. The eggs are oval, golden brown in colour and smooth; in length they are 0·59 mm.; as in all Ixodidæ they are covered with a glutinous secretion, by means of which they adhere together in masses. These egg masses may be deposited anywhere on the ground, but amongst rough, coarse herbage seems to be the favourite place. The egg stage may last as long as twenty-two weeks, or it may only take eight weeks. In the case of the bont tick a single female may deposit 15,000 or more eggs. The process of egg-laying is described as follows by Mr. Wheler: “When egg-laying is about to take place, the head is further depressed till it rests close against the under side of the body. In this attitude the end of the rostrum actually touches the genital orifice, the palpi being at the same time widely opened out. Behind the head and from beneath the shield, at what for the purposes of explanation may be described as the back of the neck, a white, perfectly transparent, delicate gelatinous membrane is brought down through inflation, either with air or with a transparent fluid, above the head, which it temporarily conceals. The end of this membrane terminates in two conical points which appear to be covered with a glutinous secretion, and at the same time an ovipositor of a somewhat similar character, but only semi-transparent, is pushed forward from the genital orifice. This latter is a tube, within which is the egg. As the ovipositor projects it turns itself inside out, like the finger of a glove, leaving the egg protruded at the end and lying between the two finger-like points of the membrane. The membrane and the ovipositor are then withdrawn each from the other. The egg adheres to the former, which collapses through the withdrawal of its contents, dragging the head forward and depositing it on the top of the head. Neither legs, palpi, nor the organs of the mouth take any part in oviposition, but after the collapse of the membrane the palpi are closed and the head is raised, by which action the egg is pushed forward to the front edge of the shield, forming in time an adherent mass of eggs, which are deposited in front of the tick.”
[The egg gives rise to the larval form, the so-called “seed-tick” stage. At first these minute specks are pallid and soft, but they soon harden and darken in colour. These larvæ are six-legged and crawl up grasses and various plants, and there await a passing host, waving their two front legs in the air and becoming attached by this means. The larval ticks feed upon the blood of the host, and when replete fall to the ground, the body becoming inflated in the meanwhile. These larvæ may remain on the host only two days, or they may remain much longer. Eventually they moult on the ground and change to the nymph or pupal stage, which has four pairs of legs. This pupa acts just as the larva, crawls up plants and waits to regain the host. After a time the nymphs, having gorged themselves with blood, fall off and remain on the ground for nearly three months; they then moult and become adult males and females. In about ten days they assume their normal colour and regain the host afresh; the female gradually swells until she attains that large inflated form so characteristic of ticks. The male does not swell, but nevertheless feeds upon the host and fertilizes the female.
[The act of coitus is strange: the male tick inserts its rostrum and other mouth organs into the sexual orifice of the female, between the base of the posterior pair of legs. The males then die and the females fall to the ground and deposit the ova. There are variations in the different species, of course, from those given above, which apply solely to Ixodes reduvius. The larvæ and nymphs seem to attack most animals, but the adults mainly keep to the same host. The periods in the life-cycle of ticks not only vary in the different species, but in each species according to climatic conditions; for instance, in the bont tick (Amblyomma hebræum, Koch), Lounsbury has shown that the development is rapid in summer, slow in winter. The period from the time that the female drops to the time she commences to lay eggs varied in specimens observed by him from twelve days in summer to twelve weeks in winter, and the complete period from the dropping of the female to the hatching of the eggs, from eleven weeks in summer to thirty-six weeks through the winter. Other stages vary in a similar manner.
[Ticks may live a long time away from the host provided they are supplied with a certain amount of moisture. Mr. Wheler kept dog ticks (Ixodes plumbeus) in the larval stage for ten months; the pupæ, male and female, of I. reduvius for six months.
[I have kept Ornithodorus moubata alive for eighteen months without food.