I have blue Vervain in my garden. Putting it there on purpose a couple of years ago with the intention of building up the population for my future rain/wet prairie garden on the far side of my yard, I planted some seed, and they have been growing in one spot for a couple of years now.
When I went out to weed today, I noticed there are a few coming up here and there in spots where they don't belong, but also along with them, there is a beetle with wings about 3⁄8 to ½ inch long walking around and on them. They are long and black with a red head. Oh no, I think to myself, not another critter to eat my plants.
So I gather a few up and decide to find out just what plants they're going to eat and by gathering them up maybe they won't devour the whole garden while I'm looking them up.
Typing Vervain + bug into my search bar, I come up with USDA Plant fact sheet with the insert saying "In addition the thread-waisted wasp, bee flies, thick-headed flies and golden soldier beetle are also known to all visit blue Vervain." Interesting. It wasn't gold but what is a soldier beetle? I go into the pdf, but not a thing is said about soldier beetles.
So I copy paste and search soldier beetle into the search engine, and here comes the spitting image of my little critters. And it turns out they're good bugs aka leatherwings. Related to fireflies without the luminescence, they are known to "feed on the eggs and larvae of beetles, grasshoppers, moths and other insects. Adults feed on aphids and other soft-bodied insects, but mainly on flower nectar and pollen. In some instances soldier beetles may appear to swarm linden trees in full bloom, where they can feed on a mixed diet of pollen, nectar and small insects" (ref Mother Earth News: Soldier Beetle Facts: Attract This Bustling Beneficial By Barbara Pleasant Feb. 6, 2013).
There is a copycat bug out there that's called a blister bug, but the head doesn't look the same as my little guys. Released back into the wild, maybe they'll keep a few of the exceptionally large amount of bugs that aren't good for my garden at bay in this year of wetness. At least I can only hope.