Encyclopædia Britannica, Ninth Edition/Harvest-Bug

HARVEST-BUG, a name erroneously applied to the hexapod larval condition of a mite, not one of the Insecta, but belonging to the division Acaridea of the class Arachnida. It is very small, of a brick-red colour, and swarms both among wild vegetation and cultivated plants, especially near the sea, attaching itself, however, on the first opportunity to the bodies of human beings, hares, dogs, cats, and other mammals, and even insects. On reaching the skin, it rapidly burrows deeply into it, causing a painful itching, followed by a swelling of irritation and size varying with the individuals attacked, and enduring for several days. It is usually at the end of July or in August that these mites make their appearance; and the frequency with which they attach themselves to the lower extremities of people walking in fields at harvest time has given rise to their trivial name. The effect of their subcutaneous presence varies in different people, as above mentioned; in some it assumes so intensely painful an aspect as to originate a disease called autumnal erythrema., Such severity of symptoms is generally found in warmer climates than that of Great Britain; the mite however is plentiful, and causes much annoyance, in Scotland. Extraction with a fine needle, under a magnifying power, is the best way to get rid of the pests; but the application of a solution of carbolic acid, benzine, sulphur ointment, or any other powerful and easily diffused insecticide agent will usually soon destroy them.

The scientific name of this creature is Acarus (Leptus or Tetranychus) autumnalis, and in France it has received various common names, that of "rouget" being the best known. It has been placed in different genera by modern authors, who have hitherto considered it as a fully developed form, of somewhat doubtful affinities. The old naturalist Degeer appears to have suspected its correct status as an imperfect Acarus; but it has been reserved for the French naturalist, M. P. Mégnin, to prove from actual observation the fact that it is only the larva of a well-known mite, Trombidium holosericcum, a silky bright scarlet species often found in spring and early summer in gardens and fields. This distinguished biologist has in like manner put beyond doubt the identity of various other members of the Acaridea, hitherto dissociated. In April he found both sexes of the perfect mite, but at the end of May and in June only gravid females occurred. These in June and July deposited their eggs, from which was hatched the creature heretofore known as Acarus (or Leptus) autumnalis. As soon as this has implanted its mandibles into the skin of the individual attacked, its abdomen dilates perceptibly, finally becoming about five times as large as on leaving the egg, though the cephalothorax and limbs remain unchanged. It turns to an octopod nymph, or pupa; and after hibernation, during which the nutritive fluids imbibed in the parasitic stage are assimilated, the adult stage of a purely phytophagous Trombidium, capable of reproduction, is reached.

There seems every reason to believe that the skin irritation caused in Mexico by a supposed insect, called Thalsahuate or Tlulsahuate by the Indians, is really produced by this or a closely allied mite. Similar complaints are apparently caused by mites in Brazil, Martinique, Honduras, &c.; and the symptoms are naturally aggravated in such tropical localities.

An account, with figures, of all the stages of Trombidium holosericcum and the allied T. fuliginosum (of which the octopod T. phalangii, parasitic upon very long-legged spiders, is the nymph or pupa) will be found in the Annales des Sciences Naturelles, 6^me série, iii. (1876), article No. 5, by M. Mégnin.