Oil beetle (Meloe impressus) is an infrequent, medium-sized, blister beetle. Its metallic blue body stands out in sharp relief against green foliage. It lives about one year but has a short season above ground. Adults are active for just two months between August and October. They are found on the ground or on foliage close to the ground. When threatened or mishandled, they exude an oily yellowish liquid that causes blistering on human skin.
Oil beetle larvae pass through four stages and seven molts (instars) before pupating. They live in the nests of solitary, ground-nesting bees, feeding on bee eggs, honey, and stored pollen.
Oil beetles (genus Meloe) are identified by head, body, and legs all metallic blue or black; oval-shaped abdomen; small outer wings (elytra) that overlap at the base and are much shorter than the abdomen; lack of functional inner wings; and antennae that are bent in the middle. This oil beetle (Meloe impressus) is distinguished by the usually brilliant metallic blue, violet, or green, sometimes black coloration; upper margin of the eye that is nearly straight; fifth segment of the antennae enlarged and flared outward; sparse, fine pitting on the head and thorax; thoracic plate with straight sides that converge toward the rear; and a spur on the fourth segment of the hind leg that projects toward the rear.