Grallipeza nebulosa is a species of stilt-legged fly from the family Micropezidae. These little guys are notable for their “dancing” — they can often be seen running back and forth, waving their brightly marked forelegs around. The tiny white feet are visible even at a distance to the human eye.
There is not a lot written about stilt-legged flies, but it seems to be the general consensus that the waving movements of the brightly marked forelegs are meant to imitate the antennae of wasps, possibly so the fly can convince predators it is, in fact, a pointy wasp and not a juicy fly. Grallipeza and many of their cousins also have a long section on the end of their abdomen which resembles a stinger. Not every species waves its forelegs as part of its disguise; some wave their back legs instead, and some species of stilt-legged flies employ elaborate backwards “moonwalks” to emulate local species of stinging ants.
Here’s a neat video of some other species of stilt-legged flies showing off their behaviors:
Video courtesy of Bug of the Week.
Adult stilt legged flies are often predators who also feed on decomposing organic matter. Larvae can be found in soil, on rotting logs, and in feces. Adults are roughly 10 mm long, with long, thin legs and narrow wings.