My long-time friend, one-time advisor (for my MSc degree program), and world’s leading Dipterist (as selected in 2018 by the North American Dipterological Society- NADS), Dr. Steve Marshall, has amazed me again with another incredible photograph, this time of a pair of mating Phalacrotophora halictorum in flight (male on the left, female on the right). The interesting thing about this photo, besides the almost impossibility of capturing these little 1-2 mm long flies in flight, is the information about mating that it provides. Look at the precise placement of the male’s front legs and middle legs on specific parts of the female abdomen. This is not a male that is just holding on for dear life as it flops along attached to the female: this male is touching her in very specific parts of her body, presumably as a type of external courtship to convince the female to use his sperm. This photo gives us:

1- Potential phylogenetic information to compare with other, related flies when we observe where they touch their females while in flight.

2- Sites to examine on the bodies for specialized sensory structures. For instance, the female abdomen must have some kind of receptors that allow it to register the touch of the male. Insects don’t have highly sensitive skin like we do, they have an exoskeleton that has specific sensory structures, usually hair-like setae, that allow them to detect touch. Likewise, the male legs probably have some kind of structures that are used to stroke or otherwise stimulate the female. I’ll be looking at specimens in the collection to see if I can find male or female structures that correlate to these points of contac

3- Behavioral details that add to our ever-so-slowly increasing body of knowledge about mating patterns in phorids and other flies (see my previous post on Fly Porn).

I hope you are as impressed with this photo, and with Steve, as I am. He has a number of books featuring his photographs, including the best book ever written on flies. You can’t go wrong buying any of them.