There were a couple of dozen of these Black Blister Beetles (Epicauta pennsylvanica) ... for some reason all clustered on one goldenrod out of hundreds of others.
When it comes to survival strategies nature is endlessly inventive and blister beetles have evolved an interesting deterrent against predation. If disturbed they bleed a fluid containing cantharidin from their joints. Should a budding entomologist come in contact with this chemical it can cause painful swelling and blistering of the skin.
