Dance Flies - Empididae
Want to Dance?
The family Empididae is a common but little known group of Diptera, commonly called Dance Flies, for their dance-like flight just above the water’s surface.
There are tens of thousands of species of Diptera, the true flies, and thousands of Diptera species are aquatic. The most notable and important Diptera to fly fishers are the chironomids (family Chironomidae) or midges. But many other Diptera live in the waters we fish and one of the more common ones is known as dance flies (family Empididae).
Empidids are stream dwellers. They are widespread and common in most streams you might find yourself fishing. The adults can be easily confused with midge adults, but their behavior will give them away: the adults hover a few inches above the water in a never ending swirl-like dance, hence their common name - dance flies.
If you want to find some dance flies, the next time you go fishing on your local stream head to a well shaded pool of quite water and sit down and just watch. If any are around, you will soon see a small handful to as many as several hundred small dark winged insects dancing in a polka marathon inches above the surface. These dancing adults are looking for small insects trapped in the surface film, which they quickly dive on for their lunch. They feed by piercing their prey with a sharp proboscis and sucking the body fluids from their hapless victim.
What I find interesting, and rather surprising, is that while the adults hover just above the surface, I have never seen one taken by a trout. I assume it must happen on occasion, especially if an adult gets carried away in its dance and ends up trapped in the surface film itself. But overall I have to say that though dance flies are common, and can be abundant, they have never been important for me to imitate.
This is probably a logical place to stop this entry: dance flies, you will see them, so what? And if it is just an interest in catching fish, then yes, there’s no need to read further. But, like most things in nature, the more you know, the more amazing things you find out. And dance flies have some rather strange and unusual tricks up their sleeve when it comes to mating.
It turns out that when some species decide it’s time to start a family, the males fly off in search of a meal to present to his intended mate. But this meal can’t be just any old dead insect. If the male wants to spend the night, then dinner better be just right, and for some species this means catching a specific species of little stonefly, like an adult Isoperla (little Yellow Sally for us fly fishers). Isoperla females typically lay their eggs on warm summer afternoons and evenings, which appears to coincide with the timing of mating dance flies. On more than one occasion I’ve sat watching (when the fishing is slow, of course) the late afternoon egg laying flights of Yellow Sallies. The females open their wings five to ten feet above the water and gently glide down to the surface where a small ball of eggs is released. But when dance flies are in the mating mood, these slowing falling Isoperla females are just what the males (or should I say females) desire, for out of nowhere a male empidid dives in and flies off with the stonefly firmly in his grip. After presenting a female empidid with his prized catch, and she is sufficiently impressed, the male gets to pass on his genes and the female gets a good dinner in the process.
Interestingly the males of some species of empidids have found a way to simplify the dinner arrangement. Rather than catching a live insect to present to the female, these males produce a small ball of bright white silk. The male then presents this ball of silk to a prospective female and if she accepts then mating takes place. There is no food value to the female in this arrangement, so one can only guess that these female empidids prefer jewelry over a good dinner.
Have fun &
Happy casts!