Stalk-eyed Flies

Among the enormous assemblage called the insects, the fly order Diptera is certainly one of the most fascinating, with a host of alien-like members, many of which are also worthy of recognition- the hoverflies are remarkable aerobats, and certain fruit flies from Hawai'i have their own elaborate courtship dances. One of the most weird and wonderful groups of flies, one that literally "stands out", are the stalk-eyed flies- Diopsidae.

There are not a lot of flies that one would add to a wish-list and strike off as a "lifer" upon a sighting- but the stalk-eyed flies are an exception. Not only are they amazingly unique to observe, they are not exactly easy to find.

The first time I saw stalk-eyed flies was on TV; they were featured in the natural history documentary series Life. Later, I encountered this fly (Diopsis sps.), quite by chance, twice in real life- the first time in Arunachal Pradesh, and then a second time much closer to home, in Karnala, Maharashtra.

What is perhaps most fascinating about stalk-eyed flies (once you grasp how weird they look) is the process by which their head develops into the shape that gives them their name. After emerging from the pupa as an adult, the fly actually pumps air into its head, expanding the sides of its head near the base of its eyes. Eventually, it pushes the eyes so far out that they stand out on very long stalks.
(Here is a link to a video clip, the same footage featured in Life - http://videos.howstuffworks.com/disc...alks-video.htm)

The second unique aspect is how the males use their bizarrely shaped heads for courtship. Firstly, the farther a male's eyes project, the more superior his genes, and hence, by natural selection, he is the one that gets a mate. Secondly, stalk-eyed flies are documented using their wide heads as battering rams, headbutting each other into submission. As always in the animal world, fights do not happen without adequate warnings, and the rivals raise their wings to signal their intent. These flies are territorial, and they use these methods to safeguard their leaf (or other territory).

Stalk eyed flies are found mainly in humid forests, most commonly by stream sides, on leaves during the day and 'roosting' on exposed plant roots and stalks at night.

This fly's biology is a wonder in itself, but also turns one's attention to another, bigger wonder- the extreme lengths to which life evolves!



[Pictured in the following frames are the two stalk eyed flies I have encountered. Both were found close to streams, on short vegetation. Both were about 6-7 mm long.]

Diopsis sp. | Karnala, Maharashtra | Oct 2014

Diopsis sp. | Seijosa, Arunachal Pradesh | Nov 2013

Very interesting description of these stalk-eyed flies. When I first saw the photographs, I thought it had something like antennae. After reading the post I realised those were its eyes. Nature is really amazing. Good details. Nicely captured. Thanks for sharing the detailed description of these flies.

Never knew about this. Thanks for sharing. Now I learn a little more.

Nice write up Abhishek. very intresting.

TFS
Roopak