Hover flies of the desert SW: Copestylum spp.

Many Syrphids or Hover Flies resemble bees or wasps and may be mimics of those armed Hymenoptera, because Syrphids themselves are harmless nectar feeders. The larvae of certain species are predatory, for example on aphids.

In the desert southwest Syrphids of the genus Copestylum are very common. Almost everyone has noticed the big black Mexican Cactus Fly, Copestylum mexicanum that reminds me of a Carpenter Bee. The common name is accurate this time, Copestylum larvae feed on rotting plant material, and around here, that usually means dead cactus. If one digs through the mushy brown soup inside a dead saguaro, one will find many larvae of C. mexicanum (top left), C. isabellina (top right), and C. apiciferum (bottom left). The small C. avidum develops in dead pencil chollas and other smaller cacti.

 

Mating where the eggs will be laid: C. avidum on a Pencil cholla. They will find the dead rotting parts as prospective larval food.