Black Flies In Death Valley NP?

Jack DeAngelis, PhD

OSU Entomologist (ret.)

Summary: We found black flies, which are normally associated with fast flowing rivers and mountain streams, in Death Valley NP, one of the driest places on earth. Why?

Disclaimer

Scotty's Castle in Death Valley National Park

Black flies at Scotty's Castle, Death Valley NP

Scotty's Castle is a large, sprawling vacation home built in the 1920's by a millionaire couple from Chicago and an eccentric gold miner (Scotty) that is located at the northern end of Death Valley National Park in Nevada, USA. The house and grounds are now run by the US National Park Service and are open to visitors. Scotty's Castle draws many Death Valley NP visitors because it displays the extravagance of the 1920's "movie star" lifestyle, as many of Hollywood's biggest celebrities of the time used the house as a vacation retreat.

Scotty's Castle is located in Mojave Desert, one of the driest places on earth, yet during our last trip there we encountered hordes of biting black flies in one small area of the grounds (see What are Black Flies?). Black flies are normally associated with fast flowing rivers and streams in wet environments, so what's going on here?

Black fly biology

Black fly larvae need clean, flowing water to develop because they are attached to solid surfaces, like rocks, and feed by filtering the water that flows around them.

Scotty's Castle is located near natural springs which support dense vegetation (see vegetation in the background of photo above) in this otherwise barren landscape. These springs were tapped to provide water for the home. So much water is available that some landscape features sport permanent flowing water, which supports a vibrant black fly population!

So that's the answer to another mystery of Death Valley and some insight into black fly biology. Black flies need flowing water but not a river. Even a fairly small trickle will do as long as the water is clean.