ITHACA, N.Y. -- Reminder to tiger beetles: If you chase prey at high speeds, you'll go blind.
Entomologists have long noticed that tiger beetles stop-and-go in their pursuit of prey. But until now, scientists have had no idea why this type of beetle attacks its food in fits and starts.
The answer is that the insect's ability to see shuts down after it accelerates toward 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. "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."
In nature, such stop-and-go chase patterns are unusual, but the tiger beetle is unique. In the midst of hot pursuit, it stops three or four times to reorient itself toward the prey. Even after a few stops, the tiger beetle has enough time to overtake its prey during its high-speed pursuit.
Results from Gilbert's laboratory observations have been published in a peer-reviewed article, "Visual control of cursorial prey pursuit by tiger beetles (Cicindelidae)," in the Journal of Comparative Physiology Fall 1997.
But, just how fast is fast for a tiger beetle? Gilbert compared an ordinary tiger beetle to Olympic superstar Michael Johnson. Johnson, the world-record holder, can run 200 meters in 19.32 seconds, which averages to a speed of 10.35 meters per second (or 23.1 mph.)
"The top speed for my tiger beetles is 0.5387 meters per second (1.2 mph)," said Gilbert. "This is not very impressive, but the beetles are a lot smaller than Michael Johnson. If we scale the speed for body length, we get a much different picture."