Peterson Field Guide says: Blister beetles are common insects occurring on the flowers and foliage of various plants. The name “blister” beetles is based on the fact that the body contains cantharadin, a substance capable of blistering the skin. This chemical is extracted from the body of certain species and used medicinally. Adult blister beetles are plant feeders, and some are serious pests of potatoes, tomatoes, beets, clover, and other plants. The may completely defoliate a plant. Larvae are parasitic and generally beneficial; they usually feed on grasshopper eggs, but some feed on eggs or larvae of bees. Larvae that parasatize bees climb onto the flowers and attach themselves to bees visiting the flowers. The bees then carry these larvae to their nest, where the larvae attack the bee eggs. Meloid larvae undergo hypermetamorphosis (in which the various larval instars are quite different in form): the 1st instar is long-legged and active, whereas following instars are grublike and maggotlike. Members of the gene Meloe, which are rather large and black or bluish, have very short, overlapping front wings (elytra); they are called oil beetles becaue they exude an oily substance from the joints on the legs when disturbed; this substance can raise blisters on one’s skin.
Hmmmm….maybe I shouldn’t have picked it up!
Addendum: October 23rd. Spotted several more blister beetles in the same field today. Tried to pick one up to show a friend, and unlike the one in the photo above, went into defense mode, excreting rusty orange droplets at each leg joints. Sure wish I’d had a camera!