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!):

• Short-winged blister beetle (Meloe campanicollis) - found in central to eastern North America, from Georgia to Ottawa.

• Meloe strigulosus - found in Central America, and along the west coast of the U.S., into southern Vancouver.

• Short-necked Oil Beetle (Meloe brevicollis) - found in the United Kingdom

• Cape oil beetle (Meloe angulatus) - found in South Africa

• Black Oil Beetle (Meloe proscarabaeus) - found throughout Europe into Asia

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

Description: 

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:

• Poison touch - Cantharidin causes blistering and swelling of the skin and eyes. It is so valuable that sometimes other smaller bugs will bite oil beetles to steal their cantharidin.

• Sneaking - the triungulin hitches a ride on bees to get into their hives.

• Theft - once inside the hive the triungulin eats the pollen left for baby bees, and sometimes the eggs and bee larvae too!

Oil Beetles in Culture:

• Cantharidin is as toxic as cyanide and strychnine!

• The ancient Egyptians used oil beetle Cantharidin (the chemical responsible for the toxicity of the hemolymph) to induce labor.

• The ancient Greeks used it as an aphrodisiac and healing salve and on the other end of the spectrum, for assassinations and executions.

• It has been used in healing in Chinese medicines.

• Cantharidin has long been used to treat warts and molluscum.

• “Spanish fly” is a species of blister beetle, same family as oil beetles, and the aphrodisiac is also named for the beetle’s common name. The symptoms of this toxin were supposed to be similar in nature to sexual arousal (but really it sounds more like heat and irritation).

• The French writer Donatien Alphonse François ⁠ (the Marquis de Sade) gave Spanish fly to two prostitutes during two orgies which nearly killed them. He was sentenced to death but later got off on an appeal.

• In 1996, four young men ingested cantharidin with Kool-Aid and ended up in the emergency room. The drink was meant for one of their girlfriends.

• The European oil beetle (Meloe proscarabaeus, Meloidae) was named the Insect of the Year 2020 by the Swiss Entomological Society.

References:

auduboncnc. “The Surprising Life of the Oil Beetle by Jeff Tome • Audubon Community Nature Center.” Audubon Community Nature Center, 1 Oct. 2019, auduboncnc.org/the-surprising-life-of-the-oil-beetle-by-jeff-tome/. 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, entomo.ch/en/portrait/insect_of_the_year/insect_of_the_year_2020.

“Meloe.” Wikipedia, 16 Mar. 2024, en.wikipedia.org/wiki/Meloe. 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, www.montananaturalist.org/blog-post/oil-beetles/