Hammer Eyed Fly (Richardia telescopica)

On September 9th 2001, I encountered this hammer-eyed fly (Richardia telescopica) on STR trail (~600m mark) at La Selva Biological Field Station in Costa Rica. I was rushing on my bicycle to my field site one morning. I had to make an abrubt stop because my path was blocked by a tree fall which I believe was a Hampea appendiculata (Malvaceae). I noticed the fly on one of the branches of the downed tree. I rushed to get the camera out and set out the tripod. My first thought was that it was the famous star of sexual selection frequently seen on biology text-books: the stalk-eyed fly – Cyrtodiopsis dalmanni – (but what do I know about flies anyway?). One thing I was completely sure was that because of the exaggerated eye shape it was a male. I was only able to capture this short 54 second clip. During this short encounter the fly made a full turn exposing his body from all directions. Movement of halteres which have evolved as flight control organs were quite visible. I don’t know why he was moving his halteres even though he was stationary. Was it a reflex or an active sensory movement?

This dipteran is rather rare to encounter in natural setting. Seredipitous downing of a tree could have brought it to my view only for a brief amount of time.