Marquis de Beetle

Kelly’s Field Notes

Common Name: Oil beetle

Order: Coleoptera

Family: Meloidea (referring to molestus in Latin, as they release caustic hemolymph when molested)

Genera: Meloe

Species of Note Near You (There are around 20+ species of oil beetle in North America!):

The literature suggests they are not found at all south of Panama in South America.


Oil beetles are shiny black or dark blue in color, with small heads and large rounded ovoid abdomens. Adults are 1.2 - 3 cm in length (0.5 - 1.2 in), chubby looking and lacking hind wings. Oil beetles have overlapping wing covers, but they are very short. They cannot fly. Females have straight antennae where males have kinked antennae, which they use to hold onto females during mating.

If you see an oil beetle, do not handle it! They can secrete cantharidin laced hemolymph from their joints, which can cause painful blistering and swelling of the skin and eyes. Oddly enough, females bite males before mating to test how much cantharidin is in his system - this is because the cantharidin is stored in his reproductive organs and given to her as they mate, which she will keep in her system. When she lays the eggs they are coated in the cantharidin providing extra protection from predators. Adult females cannot synthesize cantharidin on her own, whatever they have as larvae is all they’ve got for life.

Cantharidin Note: Currently, there are more than 1500 species of cantharidin-producing beetles. Other insects are attracted to cantharidin, such as other beetles, some gnats, muscidae flies, signal flies, midges, and parasitoid wasps. Spotted lantern flies (Lycorma delicata) contain cantharidin, but they do not produce it, it is likely taken up through ingesting plants.

Life Cycle: 

Oil beetles begin life as eggs their mother lays in the dirt, in close proximity to bee nests. She can lay around 1,000 eggs. Oil beetles are hypermetamorphic, which means they have a sort of extra step in their instar stage, where it looks different than the other instars. Within this special stage the larva is called a triungulin. The triungulin is the first instar stage and looks a little like a louse or a springtail. This little guy or gal is on the hunt for a male bee, some species of oil beetle are so prepared for this they even emit a pheromone that smells like a female bee. The triungulin will wait on vegetation for the bee. When the male bee comes, the triunglin hitches a ride on his back and waits for him to mate with a female. While that is happening, it moves over to the female for a ride back to the hive or nest. Once inside the nest, the oil beetle triungulin will transform into a grub-like larva. Here it will feed on the pollen meant for the baby bees, sometimes going as far as eating the bee eggs and young as well. The rest of their instar stages are larger grub-forms until they pupate. Pupation is spent inside the bee hive or nest, warm and cozy and safe until Spring. When Spring arrives the oil beetle emerges as an adult and the cycle continues! 

Livestock Note: Adult oil beetles feed on plants. They are often found in crop fields used to produce livestock feed. If clustered in bales of feeder hay they can cause serious damage to horses, who are particularly sensitive to the cantharidin. 

Great bustards note: Great bustards (Otis tarda) become intoxicated when feeding on blister beetles (general family oil beetles belong to). Males specifically eat oil beetles (Meloe spp.) to increase their sexual arousal. Another bonus, the cantharidin works to kill parasites of these birds and bacteria that causes sexually transmitted disease.

Oil Beetle Super Powers:

Oil Beetles in Culture:


auduboncnc. “The Surprising Life of the Oil Beetle by Jeff Tome • Audubon Community Nature Center.” Audubon Community Nature Center, 1 Oct. 2019, Accessed 19 Apr. 2024.

‌Bravo, Carolina, et al. "Males of a strongly polygynous species consume more poisonous food than females." PLoS One 9.10 (2014): e111057.

Hemp, Claudia, and Konrad Dettner. "Compilation of canthariphilous insects." Beiträge zur Entomologie= Contributions to Entomology 51.1 (2001): 231-245.

“Insect of the Year 2020.” The Swiss Entomological Society,

“Meloe.” Wikipedia, 16 Mar. 2024, Accessed 19 Apr. 2024.

‌Moed, Lisa, Tor A. Shwayder, and Mary Wu Chang. "Cantharidin revisited: a blistering defense of an ancient medicine." Archives of dermatology 137.10 (2001): 1357-1360.

“Oil Beetles: One of Nature’s Tiny Celebrities | Montana Natural History Center.” Montana Natural History Center,