Thursday, August 31, 2006

Making waves

Ever noticed these black beetles in ponds when it rains, they seem to be calm and then suddenly as you approach them they go crazy. Skittering about swimming fast like madcaps? That behaviour has earned them the name Whirly-gig beetles.

They're aqautic for their entire life, eggs are laid on submerged plants. Larvae live underwater and predate on mosquito larvae making them great pest control agents. The adults are also predaceous and usually swim on the surface When required they can dive like many aquatic insects with air bubbles trapped between wings for respiration. What they seem to be most studied for is aggregation, signalling and predator response. They release chemicals when disturbed which alert the others in an aggregation.

The coolest thing about them in my opinion however is that they're eyes are split. The lower half of both eyes are adapted for underwater vision and the upper half for vision in the air!

Some of those fluid mech / engineering types have also done some work on their swimming patterns and the waves they generate. So maybe the above image is interesting to them?

2 comments:

Rahul said...

The eyes sound interesting. Any pictures? (I googled but didn't find much...)

Of course, it is easier with insects' compound eyes, than with vertebrate eyes. I imagine that even if the upper half works in air, it must work when "somewhat" wet, or have some mechanism to keep it dry.

Amazing pics, like I've said before. One of the few blogs out there with significant original content.

Natasha said...

Theres an SEM of the eye here
http://www.insectzoo.msstate.edu/OrkinZoo/pond.html
But I cant seem to see the difference between the two halves to be honest.

Theres a drawing here which sort of makes things a bit clearer.
http://www.bio.umass.edu/biology/conn.river/insect_images/whirligig.gif

Yup insect eyes which are made of many individual cells with individual lenses would make this sort of spliting easier. Have you read the paper in which they 'fabricated' a compound eye? Its thin enough to put on a credit card!

And yes they'd work when a little wet, in fact all our eyes work when wet. In a pool for instance, but vision gets worse. I think insects use some trick to prevent films of water forming so the whole eye isnt wettened...I'll look it up