Subject: Robber Fly?
Location: Watsonville, CA
June 11, 2015 2:33 am
I have been finding large numbers of this mysterious (but beautiful) fly in my front yard… I’ve done a lot of internet research and cannot for the life of me figure it out… Is it a Robber Fly??? I have found them all of my Armenian Basket Flower and Artichoke… Please help! I need to know if it’s a pest or not.
These are most certainly not Robber Flies. This is an introduced Artichoke Fly, Terellia fuscicornis, a species of Fruit Fly. Your images of a single individual are both females, as evidenced by the long ovipositor, and the image with the three flies include two males that are attempting to mate. Interestingly, bugGuide only has images of female Artichoke Flies, and they do not provide a common name. There are many nice images on the Natural History of Orange County site. As an introduced species, they may pose a threat to cultivated artichokes, but we have also found information that they use Milk Thistle, an introduced pest weed in California, as a host so the jury is still out if they are an agricultural pest or a biological control agent.