Oil beetles in the Meloidae family are chunky, hairy pollinators as adults, but, before that, they go through a complicated and peculiar life cycle.
These robust beetles are hypermetatmorphic. That means they go through more stages than the typical metamorphosing insect. Specifically, they have two distinct larval forms.
From an egg, they grow into a larva called a triungulin, which is a small, flattened creature with legs. They’re highly mobile at this stage, and their sole purpose is to attach themselves to a bee, snagging a ride back to its nest. Once in the nest, the triungulin feeds on the bee’s eggs. Different species of oil beetle specialize in different species of bees.
At its next stage, the triungulin casts off its skin and becomes a more standard, short-legged grub that feeds on the food the bee has left for its young. After a third moult, the beetle larva grows to become a grub that looks a lot like a bee larva. Finally, it makes a pupa and emerges as an adult.
Beetles in this family are also called “blister beetles.” That’s because they can exude a defensive liquid, cantharidin, that causes a painful reaction to any predator that tries to mess with them. Because the adult beetles sometimes feed on flowering crops like alfalfa, they can get into horse feed. Horses can have severe reactions to the toxin and, reportedly, horses can die if they accidentally eat too many blister beetles.
On the positive side, cantharidin is used to treat warts and has been used to remove tattoos. It’s also being studied to treat cancer.
Although several oil beetles waved their front set of legs at me when I got close with a camera, I didn’t see any oily substances near their joints.
This week, dozens of oil beetles are hanging around on a plant in the South Bottomlands. The flower looks like a small dandelion. I think the plant is Hawkweed.
Stay curious!
See more of Karen’s work here.
Sources:
Photos of triungulin’s are on Honey Bee Suite, here: https://www.honeybeesuite.com/triungulins-a-hitchhiker-riding-a-bee/ Accessed 7/24/24.
There’s a good description of the life cycle here: https://thesmallermajority.com/2012/10/08/life-saving-beetles/ Accessed 7/24/24.