Image Credit: gailhampshire
Cuckoo Hornet-mimic Bees: Megachilidae (Stelis)
On a worldwide basis, Stelis is a very diverse group of species, often separated into several genera in their own rights. In the Northwest, the largest species parasitize other groups of mason, hornet-mimic and leaf-cutting bees. The commonest species appear to be hornet-mimic bees with no pollen-transport structures, or all black hornet-mimic bees. They are extremely infrequent in collections and therefore poorly understood.
I have observed a Stelis enter the nest of the brilliant green Hoplitis fulgida in the “fossilized” air bubbles of an exposed lava flow. The female grabbed the Stelis by the wings and dragged it to the entrance and then flew out a few feet and let it go. The Stelis immediately returned to the nest burrow while the female Hoplitis groomed nearby. These activities repeated for at least 6 times, before the Stelis finally flew away (apparently completely “unharmed”).
Stelis in North America parasitizes principally the tribe Anthidiini. Stelis varies from having Hornet-bee stripes to entirely black.