Fig. 30.—Leptus autumnalis = larva of Trombidium holosericeum. Ventral view. × 100. (After Railliet.)
One of these six-legged larvae has been long known as the harvest-mite, under the name of Leptus autumnalis. But this is not a real species, and there is still considerable confusion as to what the exact status of Leptus autumnalis, the harvest-mite, is. Probably the larvae of several species are involved, but it seems pretty certain that in many cases the larvae will grow up into specimens of the genus Trombidium holosericeum, though a certain and at present unknown percentage of the larvae will grow up into Trombidium something-or-other-else.
They are minute bright-scarlet little creatures—the Cardinals of the Mite world—of a beautiful satiny red, decorated here and there with blackish spots. The body of the adult is somewhat square, tapering slightly to the hinder end. Both legs and body are covered with red hairs. The eyes are borne on little stalks—like lighthouses. The legs have six joints and end in two little claws. The male is usually smaller and more feeble than the female, the latter reaching a length of 3 mm. to 4 mm. The adults are commonly met with in the spring or commencing summer. Apparently, they nourish themselves on vegetable sap. The larval form of this species[11] is undoubtedly one of the forms confused under the now discarded name of Leptus autumnalis. When starving, the body is orbicular in outline, but it becomes oblong when it is fed, and in this case it may attain a length of ½ mm. Its colour is of a deep orange.
Fig. 31.—Leptus autumnalis, with the so-called proboscis. Magnified. (After Gudden.)
This harvest mite, or, as it is called in France le rouget, is most troublesome at the end of summer or at the beginning of autumn, when it is found in enormous numbers in grass and amongst many other plants—gooseberries, raspberries, currants, haricot-beans, sorrel, and elderberries. From these plants it passes on to any warm-blooded animals: particularly it attacks small mammals. Hares, rabbits, and moles are often covered with them, but they leave their victim, should it be shot, as soon as the body chills. They are particularly common in Great Britain and in the centre and west of France, and in certain parts of Germany. These irritating little semi-parasites may be dislodged by the application of petrol or benzine—both very inflammable—and the itching they cause allayed by the application of acid or alcoholic lotions.
Fig. 32.—Leptus autumnalis (× 100). The so-called proboscis is formed around the hypo-pharynx sunk into the skin. (After Trouessart).
Men working in the fields are frequently attacked. During September 1914, the soldiers of the Sixth Division, stationed in and about Cambridge, and living in tents, suffered severely from their ‘bites.’ They mostly attacked the ankles, the wrists, and the neck, but they rapidly extend over the body. If they be checked by the presence of any stricture, such as a garter or wrist-band, they accumulate behind it, and the irritation is accentuated. The presence of their hypo-pharynx in the skin causes the surrounding tissues to harden and form a cylindrical tube—the so-called proboscis.