Genus Meloe - Oil Beetles

Meloe Linnaeus 1758

22 spp. in our area(1)

12-30 mm(2)

Hind wings absent; elytra reduced and overlap at base. Males smaller than females, with modified antennae(2)

Male antennae

Holarctic genus; throughout NA to Mexico & West Indies(1)

Ground or low foliage(2)

Larvae feed on eggs and other food in bees' nests(2)

In at least some species of Meloe, triungulins aggregate and use chemical signals to attract male bees to which they attach themselves. This allows transport (and transfer) to a female bee who carries them back to her nest (Saul-Gershenz and Millar, 2006).

Beetles emit an oily substance from leg joints when disturbed (thus the common name)(2)

Per Seago & Wheeler (2004): Enlargement of mid-antennal segments does occur in some blister beetles (Meloidae), notably in the genus Meloe (Linnaeus). Several North American species of Meloe have c-shaped ‘‘kinks’’ involving antennomeres V–VII, thought to be involved in courtship (Bland 1986). Males of M. niger have been observed using their modified antennae to grasp females by their antennae during pre-mating displays (Pinto and Mayor 1986).

Jim McClarin refers to these pre-mating displays as, "antennal foreplay"(3)

First-instar larvae climb to the top of a grass or weed stalk as a group, clump together in the shape of a female solitary ground bee, exude a scent that is the same as, or closely resembles, the pheromones of the female bee, and wait for a male ground bee to come along. When he does, he tries to mate with the clump of larvae, whereupon they individually clamp onto his hairs. He then flies away, finds and mates with one or several real female bees, and the larvae transfer to the female(s).

Each impregnated female bee then flies off and builds one to several nests in burrows she digs in the soil, and the larvae transfer again to the new nests. The female bee stocks these nests with honey and pollen for her own young, but the hungry blister beetle young are there to gobble up the provisions. They eventually pupate and finally emerge as adult flightless beetles. Brothers and sisters find each other and mate, produce eggs and the hatchlings start the process all over.

Then there are male beetles from a couple other beetle families who seek out blister beetles, climb onto them and lick off the cantharidin the blister beetles exude. Not only have these other beetles developed a resistance to the cantharidin, they use the blistering agent to impress a female of their own species who then mates with them, whereupon most of the cantharidin is transfered to the female in the form of a sperm packet. The eggs the female subsequently lays are coated with cantharidin to protect them from being eaten before they hatch.

Then there are the bipedal primates who use cantharidin from blister beetles to manufacture the notorious date rape drug, Spanish Fly...

(Jim McClarin's comment)