15.2.2. Blister and urtica (itch)-inducing insects
Some toxins produced by insects can cause injury to humans, even though they are not inoculated through a sting. Blister beetles (Meloidae) contain toxic chemicals, cantharidins, which are released if the beetle is crushed or handled (see Plate 6.3). Cantharidins cause blistering of the skin and, if taken orally, inflammation of the urinary and genital tracts, which gave rise to its notoriety (as “Spanish fly”) as a supposed aphrodisiac. Staphylinid beetles of the genus Paederus produce potent contact poisons including paederin, that cause delayed onset of severe blistering and long-lasting ulceration.
Lepidopteran caterpillars, notably moths, are a frequent cause of skin irritation, or urtication (a description derived from a similarity to the reaction to nettles, genus Urtica). Some species have hollow spines containing the products of a subcutaneous venom gland, which are released when the spine is broken. Other species have setae (bristles and hairs) containing toxins, which cause intense irritation when the setae contact human skin. Urticating caterpillars include the processionary caterpillars (Notodontidae) and some cup moths (Limacodidae). Processionary caterpillars combine frass (dry insect feces), cast larval skins, and shed hairs into bags suspended in trees and bushes, in which pupation occurs. If the bag is damaged by contact or by high wind, urticating hairs are widely dispersed.
The pain caused by hymenopteran stings may last a few hours, urtication may last a few days, and the most ulcerated beetle-induced blisters may last some weeks. However, increased medical significance of these injurious insects comes when repeated exposure leads to allergic disease in some humans.