|Black Blister Beetle – Epicauta pennsylvanica|
Family Meloidae – Blister Beetles
Live adult blister beetles photographed in the wild at DuPage County, Illinois, USA
These black blister beetles are feeding on goldenrod pollen (Solidago sp.) Blister Beetle adults feed on leaves in the tops of a plant but are especially attracted to flowers where they feed on nectar and pollen. These beetles are mid to late summer insects, active in mid-July into September.
Female blister beetles lay clusters of eggs in the soil in late summer. The small, active larvae that hatch from these eggs crawl over the soil surface entering cracks in search for grasshopper egg pods. On finding a grasshopper eggmass, the larvae eats it, then becomes immobile and spends the rest of its larval time as legless grubs. The next summer they pupate and soon emerge as adults. Blister beetle populations follow closely the abundance of grasshoppers the year previous.
“Blister beetles produce cantharidin, a poisonous substance comparable to cyanide and strychnine in toxicity. The substance, stored in the insects’ blood, is very stable and remains toxic in dead beetles. Animals may be poisoned by ingesting beetles while grazing or eating harvested silage. Cantharidin can also cause severe skin inflammation and blisters.
Cantharidin is absorbed through the intestine and can cause symptoms such as inflammation, colic, straining, elevated temperature, depression, increased heart rate and respiration, dehydration, sweating, and diarrhea. There is frequent urination during the first 24 hours after ingestion, accompanied by inflammation of the urinary tract. This irritation may also result in secondary infection and bleeding. Taken internally, as little as 10 milligrams can be fatal in humans.
The concentration of cantharidin in adult beetles depends primarily on the sex; males produce the chemical and only pass on small amounts to the females during mating.
Cantharidin amounts also depend on species; the striped blister beetle has approximately five times more catharidin than the black variety. In one species, MÃ©loÃ© proscarabaeus, cantharidin makes up fully 1/4 of the insect’s blood.
There are other insects, including some beetles, flies, bugs that eat live or dead blister beetles to obtain the protective qualities of this chemical defense; these so-called cantharidinophilous insects have acquired immunity from the chemical and remain unharmed.” 
Male fire-colored beetles in the family Pyrochroidae are known to climb onto blister beetles and ingest the cantharidin exuded by the insect. Completely immune to the effects of the blistering agent, they use the chemical to attract females, who become the recipients of a cantharidin-laden sperm packet with which they coat their eggs.
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Order Coleoptera: Beetles are the dominant form of life on earth: one of every five living species is a beetle. Coleoptera is the largest order in the animal kingdom, containing a third of all insect species. There are about 400,000 known species worldwide, ~30,000 of which live in North America. Beetles live in nearly every habitat, and for every kind of food, there’s probably a beetle species that eats it.