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7. Blister beetles. IMG_5106.jpg

7. Blister beetles. IMG_5106.jpg

December 21, 2010.

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Dr. John Carlson contributed the following by email:

This is an aggregation of blister beetles; a number of species respond to an aggregation pheromone, and can cause significant problems. Scrubbing the walls where they have aggregated may remove some of the pheromone, and setting up an alternate shelter may encourage the use of another space for their congregations. The sheltered space of the school must meet the characteristics they are looking for, and it may be difficult to convince them to relocate after an initial aggregation has sent out the pheromones.

I would ask local folks if they have experienced such outbreaks of these beetles in the past- particularly the older members of the community. People tend not to forget their experiences with these animals. Ask them how long the aggregations have lasted in the past and this may give you an indication of how long the problem will last this time. While there are probably aggregations every year, there can be tremendous variation in population sizes, and tendency to aggregate.

There is no good treatment for the wounds. The cantharidin from the beetles causes direct injury to the inner layers of the skin, and the fluid that oozes from the skin is filled with protective immune cells. The chemical does not disrupt the outer layers of the skin, which is why they produce blisters rather than ulcers. The tissue will repair itself- it just takes time, and this happens more quickly for blisters than for ulcers, so it is best not to remove the outer layer of skin. Over time, people can develop allergic reactions to the cantharidin, and in those cases the redness and itch will be far worse than the typical lesions, and last weeks longer. In those cases a steroid ointment is the best treatment, applied twice daily to the inflamed skin while it remains itchy. Antihistamines are not very effective. A cool compress is much more effective at treating the itch from these types of reactions, and is underappreciated in treating the symptoms of blister beetles. Ice should not be used.

The cantharadin of the Blister beetle works by breaking the connections between skin cells and is enzymatic. This is what causes blisters.

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Email communication to Dr. Amy Eisenberg on December 30, 2010:

The beetles on the photos belong to False Blister beetles family (Oedemeridae), the genus possibly is Nacerdes. We have a similar, as well toxic species in Europe. Since the poison in the blood is the same as in Meloidae, that does not change much, except for prevention. Those beetles do not actively drop their poison, but have to be smashed on the skin first.
Also, the school building should be checked for being possibly the source. Nacerdes and allies develop in damp rotting wood, and stains on the walls make me think that rotting palms may be infected with the beetles.

Best wishes!

Boris Büche, Berlin, Germany.


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Brenda 23-Jul-2011 18:41
I found one of these bugs in my kitchen..we have a very large wood pile that is about 8 feet from the house. Could they possible come from out there? And,can I expect more to come? I let my dogs out late last night and I thought possibly that's how it got in the house.Thanks again for your help!! Sincerely, Brenda
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