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Black Blister Beetles Consuming Asters

9-7-18 black blister beetle_U1A8536

Blister beetles are so-called because they contain a chemical in their hemolymph, or blood, called cantharidin.  If rubbed or pressed the beetles release cantharidin as a defense mechanism, which causes blistering on human skin.  The Black Blister Beetle (Epicauta pennsylvanica) belongs to a genus of beetles that are highly toxic to horses — a few beetles fed in a single feeding of alfalfa can be lethal.

As larvae, most blister beetles are predators, often invading wild bee colonies and consuming bee larvae, as well as nectar and pollen.  Black Blister Beetle larvae and other blister beetles in the genus Epicauta prey on the eggs of grasshoppers.  Female Black 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 of grasshopper egg pods which are deposited in the ground. After finding an egg mass, the blister beetle larvae become immobile and spend the rest of their developmental time as legless grubs. The following summer they transform into the pupal stage and soon emerge in the adult stage. This is why blister beetle numbers increase dramatically following high grasshopper populations.

Once they mature into adulthood, Black Blister Beetles feed on plants (phytophagus) and are commonly found on flowers, especially those in the Aster/Composite family. They are said to be there for the nectar and pollen, but the Black Blister Beetle pictured denuded several aster blossoms of all petals during the time it was observed.

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7 responses

  1. Alice Pratt

    Interesting, but a Little Black Menace 😮

    September 14, 2018 at 8:57 am

  2. Robyn Deveney

    Killing bees and demolishing asters – this is a hard beetle to like.

    September 14, 2018 at 11:00 am

  3. Do these guys serve any good purpose? Does anything feed on them?

    September 14, 2018 at 2:12 pm

    • I have read that there are birds that do eat them, though I’ve never observed this firsthand!

      September 15, 2018 at 5:15 pm

  4. Kathryn

    The beautifully colored blue blister beetles totally annihilated a gorgeous jack-in-the-pulpit plant and my fall blooming clematis. I do not LIKE blue blister beetles!!

    September 16, 2018 at 10:26 am

    • Judging from the responses to this post, Kathryn, you have a lot of company!

      September 16, 2018 at 6:01 pm

  5. Jon Binhammmer

    I think more people need to check their anthropocentrism at the (virtual) door! Blister beetles are a native insect that plays a role in the unbelievably complex ecosystem that we happen to also live in. Sometimes insects and other life in this web annoy us, but the more we use a binary approach to wild things, eg. good vs. bad, the more we are able to unravel the web of life that sustains other life, and ultimately, us!

    September 17, 2018 at 3:47 pm

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