Black oil blister beetle - The strangest beetle I have ever photographed.

Black oil blister beetle eating spring whitlow grass.  Kelowna, early April.

Our daughter was visiting us, and it seemed like a good idea to walk along the trails in the upper section of Mission Creek Park in Kelowna.  It was a banner day, both for enjoying the outdoors and finding insects that emerge early in the spring.  I photographed a half dozen of these 6-legged invertebrates, and the oddest of the bunch was the black oil blister beetle.

It was hard to miss; the beetle's enormous abdomen was comical in proportion to the rest of its body.  Our youngest thought it must be a gravid queen ant.  I thought about picking it up, but there was a good chance it may have contained Cantharidin, that nasty chemical that blister beetles possess.  I have caught a good many beetles in my time, and my beetle senses (similar to spider senses, but less fun) proved me right.  It was, in fact, a blister beetle.

Part of the reason for my daughter's pronouncement was that the creature had no wings.  These guys have short wing covers (elytra) with no wings.  The fact it had a straight pair of antennae meant it was a female.  We watched her mow through the spring whitlow grass, unmoved by our presence.  (See photo at the bottom of the blog).  I have no doubt she was feeding whatever offspring were gestating inside her.  

Black oil blister beetles lay their eggs in the ground near flowers frequented by bees.  The young larva crawls up a nearby flower and awaits a ride.  When a mining bee comes along, it hitches a ride back to the underground nest (read this post on mining bees), where it detaches itself.  There, it eats the food provided for it by the unwitting bee and eats the bee larva for good measure.  

However, it doesn't end there.  The growing beetle (technically a grub) will finish off one cell and find another to decimate.  It will usually consume two or three such cells in its bid to grow.  The grub finally undergoes pupation and waits until the spring, when it emerges and continues the life cycle.

Cool bug.  Cool life history.  Cool photo.  This was a good find.

Thanks for reading.

Eric Svendsen     www.ericspix.com

Female black oil blister beetle engaged in devouring spring whitlow grass.