1. BLISTER BEETLES
(Order: Coleoptera; Family: Meloidae)
[Illustration: (unlabelled)]
Identification. The Meloidae are narrow elongate beetles characterized
by a “neck” (pronotum) which is distinctly narrower than its head or
wings. Adult beetles range in body length from 1 to 2 cm (0.4-0.8 in)
and vary considerably in their coloration.
Distribution. In general, blister beetles are found in greater numbers
in the western half of the United States.[5]
Biology/Behavior. The immature stages of the blister beetle are usually
predacious on other insects and are not harmful to man. Adult blister
beetles release a clear amber fluid by rupture of thin membranes in the
leg joints or other segmented areas of the body. The release of this
fluid, which contains a vesicating agent called cantharidin, is
triggered by pressure against the body of the beetle. Light pressure
exerted by clothing or by brushing off a beetle is usually sufficient to
cause the release of its vesicating fluid. The adult blister beetles are
readily attracted to bright white light, and many cases of human
exposure occur at night around such lights. Since the adults are plant
feeders, some cases of human vesication occur as persons move through
vegetation infested with blister beetles.
Avoidance/Control. In areas with an abundance of blister beetles, use
yellow light bulbs for outdoor lighting. If a meloid beetle lands on the
skin, blow it off, do not crush it. Since cantharidin is distributed
throughout the beetle’s body, crushing the beetle against exposed skin
would result in maximum cantharidin exposure. Dermatoses resulting from
blister beetle contact are seasonal, with the greatest number of
vesicating incidents in the United States occurring in July, August, and
September. Chemical control usually is not recommended because of the
mobility and wide distribution of blister beetles.
Envenomization Reaction/Treatment. This information is not included in
the appendix because the envenomization reaction generally consists of a
superficial linear bulla which does not require emergency treatment.