Gray blister beetles

Yesterday evening, James suggested that we go finish a project that involved peeling off letters from a roadside sign less than a mile away on Ranch Road 1623 in Blanco. Good idea! So I sprayed on some insect repellant, he put on long pants, and off we went. When we got to the site, right away I noticed some mounds of buffalo burr (Solanum rostratum) in bloom. I think buffalo burrs are pretty, but most would consider the species a weed because of its prolific prickles and toxicity. The plant is a member of the nightshade family (Solanaceae), like tomatoes and datura.

When I peered closer, I observed LOTS of long gray beetles feasting away on the leaves and even the flowers. Naturally, after we finished our job, James drove me back to the house so I could grab my camera. This was just too interesting not to document.

I've since learned–thanks to Bugguide.net and entomologist Mike Quinn–that these are gray blister beetles (Epicauta albida). Mike pointed me to his Blister Beetles of Texas and Important Texas Beetle Resources pages. 

Normally, I'm game to handle most beetles. But something about the ferocious-looking appearance of these warned me not to. So I didn't. And good thing I stuck with my instincts. "Are they safe to handle?" I asked Mike. No. "Blister beetles are known to cause blister outbreaks," he replied. Hence, their common name.

This irritating ability comes from their hemolymph (an insect's version of blood), which triggers blistering on contact with human skin. The blistering agent is called cantharidin, which can be highly toxic to mammals. Horses have died by eating blister beetles trapped in baled alfalfa hay. For humans, the blistering is uncomfortable but soon diminishes on its own with no medical treatment.

Online, I found an extensive research study on the species, "Ecology, Behavior, and Adult Anatomy of the Albida Group of the Genus Epicauta.) Most of the study was over my head, but I did pick up some bits and pieces.   

"Adults of all species of the group are found most frequently and in greatest abundance along roadsides, near ditches, in swales, and in other situations where the amount of soil moisture is sufficient to support the growth of herbaceous plants through the summer season," the study states. "Many of the food plants of the adults are to palatable to range animals, and adults may occur in great numbers even in heavily grazed pastures and ranges. Indeed, because of the variety of weedy plants utilized by the adults, it seems likely that the group has benefited from both grazing of livestock and cultivation of the land."

The study goes on to state that the preferred food host are plants in the nightshade family, most importantly those in the Solanum genus. 

Also, adult beetles "are characteristically gregarious... Within aggregations or groups, adults commonly rest, feed, clean and perform other activities in close proximity to other individuals..."

Check, check, check! Our gray blister beetles were definitely feeding together on Solanum along a road. So interesting! Right?