Evolution

Tiger Beetles: Part 3

Tiger beetle larvae have quite remarkable abilities, but what happens when the grub pupates into an adult? Well, it trades in its wind-powered wheel locomotion for something just as odd - it gets the ability to run so fast it can't see.

Tiger beetles pursue their prey in a very distinct manner - they sprint, stop, sprint again until they catch their target. This stopping do

esn't really make a difference in the pursuit, as tiger beetles are among the fastest insects (and among the fastest creatures when speed is scaled for body length). The Australian tiger beetle Cicindela hudsoni is 20mm long and has a top speed of 2.5 metres per second. That's 125 body lengths a second - a feat a human sprinter could only equal if he could run 200 metres in 0.87 seconds.

So why stop-start sprints? It's the only way it can refocus its eyes on its prey. "If the tiger beetles move too quickly, they don't gather enough photons (illumination into the beetle's eyes) to form an image of their prey," explained Cole Gilbert (Cornell professor of entomology), who authored a paper on this in 1997. "Now, it doesn't mean they are not receptive. It just means that at their speed during the chase, they're not getting enough photons reflected from the prey to make an image and locate the prey. That is why they have to stop, look around and go. Although it is temporary, they go blind."

Photo credit: John Flannery.

To read Gilbert's paper (though it's quite heavy-going), click here: http://bit.ly/11SJ5Al

Another paper that briefly touches on it (and is more easy going) http://bit.ly/RHM9xl

http://www.news.cornell.edu/releases/Jan98/TigerBeetle.bpf.html

http://archive.constantcontact.com/fs095/1102968923571/archive/1105911182658.html