blister beetle

Any of a small group of medium sized (3-20 mm/0.1-0.8 in) often brightly coloured beetles. Most give off an evil-smelling liquid, containing the irritant cantharidin, from the joints of their legs as a defence mechanism. When in contact with human skin, the liquid causes inflammation and blisters.

Classification Blister beetles are members of the family Meloidae, order Coleoptera, class Insecta, phylum Arthropoda.

The general characteristics of the group include: head strongly bent downwards, narrow neck, and cylindrical and fairly soft body.

The Spanish fly Lytta vesicatoria was used to produce cantharidin for medicinal purposes, when blistering was a common medical treatment.

Blister beetles have a remarkable life history, in which the larvae assume a different form after each moult. Such a type of development is known as hypermetamorphosis.

Typical life history The eggs of Sitaris muralis are deposited close to the nests of the bee Anthophora about August. The first-instar (the instar is the stage in between moults) larvae that hatch out of these eggs are called triungulins. Usually triungulins are very active (with well developed legs), hard-skinned larvae. In the case of S. muralis, however, the newly hatched triungulins are not very active and hibernate until spring. After this they become more active and some of them manage to attach themselves to the bodies of the female bees, and are thus introduced into the nests.

The bee supplies each cell of the nest with a quantity of honey and a single egg. The triungulin larva alights on the egg and is imprisoned in the sealed-up cell. It feeds on the egg, then changes into the second-instar larva, of different form and with vestigial legs. The second-instar larva feeds on the stored honey and changes into a third form of larva, the psuedo-pupa. The adult beetle subsequently emerges.