Massive Black Fly aka Mexican Cactus Fly

Earlier this week I was outside being interviewed about Entomophagy, the practice of eating bugs. While they were setting up the camera and sound equipment I took a few moments to see what insects were visiting the bright yellow flowers on the bush I was standing next to. Among the usual honeybees, I saw a massive black fly. This fly was huge (3/4 of an inch in length) and really stood out against the yellow flowers.

It was a Mexican cactus fly, Copestylum mexicanum, feeding on nectar, and this was the first time I had seen them around the Museum!

Here's what Flower Flies of Los Angeles County book has to say about them:
"This is the largest flower fly in Southern California, with a body length of 18mm. It gets its name from the larvae that feed in wet decaying prickly pear cactus. Adults are commonly seen feeding on flowers. Although it resembles some carpenter bees this species looks more like a large horse fly. The Mexican cactus fly is found from the southern USA to Central America, but related cactus-feeding flower flies are found in Mexico and South America. Many other species of the large genus Copestylum are found in our area. None of them resemble the cactus fly; instead they mimic bees and other stinging insects. All feed on decaying organic matter."

*Thanks to Museum Curator of Entomology, Brian Brown, for identifying the fly!

Aphid Eating Flower Fly Found in North Campus

There are over 150,000 species of flies in the world! Most visitors who come to the Museum can name only a few of these flies (house fly, horse fly, or mosquito for examples) and many hold the belief that we would be better off without flies in our world. On Wednesday, January 18, we found a fly that I am sure will help you realize that all flies can't be cast as "bad" characters — I introduce the humble aphid eating flower fly, Eupeodes volucris.

Female Eupeodes volucris

Photo taken by Jerry Friedman

Why do people like these flies and not others? This isn't an easy question to answer, but I'll have a go... First of all, these flies eat aphids and as any gardener will tell you, aphids are a serious garden pest. Secondly, they belong to a family of flies known as “flower flies” so called for their proclivity to visit flowers and suck down nectar. Thereby they play a role in pollination. Finally, if you look closely at these small flies you'll see why a lot of geeky people, like myself, think they are quite beautiful. Not only are they brightly colored and highly patterned, when their eyes catch the sunlight just right they have an iridescent sheen! Although I might add that E. volucris isn't as flashy as its close relative, the aptly named stripe-eyed flower fly, Eristalinus taeniops, also a native to the Los Angeles area.

Stripe-eyed flower fly

Photo courtesy of What's That Bug website

How does a fly eat an aphid? It is actually the larval stage of the fly, or maggot that chows down on aphids. Much like immature ladybugs they trawl through a sea of aphids on a plant and chomp any that get in their way!  Though they don't have quite the same look as a ladybug! 

Flower fly maggots eating oleander aphids

Photo courtesy of What's That Bug website

To find out more our local flower flies, swing by the Museum gift shop to get a copy of our latest entomological publication, Flower Flies of Los Angeles County.

Thanks to Brian Brown and Jim Hogue for supplying fly information and identifying the fly specimen.