14 Nebraskaland • November 2019
DON'T MESS WITH OIL BEETLES
By Chris Helzer
Among all the crazy life stories of all the crazy insects
in the world, the oil beetle ranks as an elite. The oil beetle
is a plant-feeding insect in the blister beetle family. As
with other blister beetles, the oil beetle produces a toxic
compound called cantharidin that is used to protect its
eggs from predation. In addition, when an oil beetle feels
threatened, it secretes a yellow substance from its leg joints
(of all places) that contains enough cantharidin to cause
immediate swelling and blisters to the skin of potential
predators. Don't mess with oil beetles, people.
However, blister-inducing yellow goo is only a small part
of the oil beetle story. Oil beetles also go through a unique
process called hypermetamorphosis as they move from egg
to adult. Instead of hatching out of an egg as a slow fat grub,
oil beetle larvae are called triungulin, and look like tiny little
silverfish. It's these speedy triungulin that take the oil beetle
story over the top.
Shortly after hatching, oil beetle triungulin cluster
together and emit a chemical that mimics the pheromone of
a female solitary bee (a bee that raises broods individually, as
opposed to in a colony with a queen, workers, etc.). Passing
male bees, sensing the female pheromone, descend upon
the mass of triungulin to mate with it. Instead, the speedy
larvae crawl up onto the male bee and hang on tight. When
that male bee finally meets and mates with an actual female
bee, the triungulin quickly transfer to their new ride and
hitchhike back to the female's nest.
Once they arrive, the triungulin hop off the female and
proceed to eat all the bee larvae in the nest, along with
the pollen and nectar the female had supplied her babies
with. Once they've destroyed the bee nest, the triungulin
transform into the kind of grub-like larvae usually associated
with beetles, and from there they pupate and turn into
herbivorous adult oil beetles.
If you ever find yourself reaching toward a fat flightless
black beetle, think carefully before you pick it up. If it's an oil
beetle, you might soon find yourself suffering from painful
blistering skin. While you apply salve to your throbbing
fingers, though, remember that it could be worse. At least the
beetle's larvae aren't going to invade your home as a swarm
of baby-eating marauders!
Chris Helzer is the Nature Conservancy's director of science
in Nebraska.
IN THE FIELD
PHOTO
BY
CHRIS
HELZER
