The fly and the eye stalk

In this section, saevus brings to you short stories of life from the undergrowth. These critters often escape our attention but they can be of immense importance in the natural world.

The macro-forests, be it in a rainforest or our urban gardens, veil some extraordinarily weird creatures, and the bizarre stalk-eyed fly definitely ranks high among them. Two compound eyes, each based at the end of elongated stalks, definitely makes for a peculiar appearance, which has for decades attracted the attention of both naturalists and geneticists.

The position of the eyes offers an exceptional binocular vision. In fact, about 70% of the sight seen by a stalk-eyed fly is seen by both eyes; compared to about 40% of binocular vision humans have; this is exceptional! It comes as no surprise thus that the behaviour of these flies is more dependent on their vision. Male flies, which have much wider stalks compared to females, hold on to temporary territories during the day, while at night the flies gather together to roost in small numbers. remarkably, the flies are born without the stalks and look pretty much like normal dipternas. shortly after they emerge from the pupa, the flies start taking in air through the oral cavity to blow up the stalks!

 

 

Pic credit- Yuwaraj Gurjar

 

The extremely long eye stalks of the males serve another purpose as well – females choose to mate with males possessing the longest stalks. This fact invited the curiosity of several geneticists, who have tried to study and figure out the determining factors which have shaped the evolution of this unique fly. Whether we figure it out or not, over a 100 species of stalk-eyed flies continue to thrive in the tropics around the world, without a bother about why they have the long stalks.

This article was originally published in the April 2015 edition of Saevus magazine.