 The Sneaky Predator
|
June 4, 2003 — Strange as it may seem, dragonflies use movement for their camouflage, according to a study published Thursday in the British journal Nature.
Camouflage is usually associated with immobility: a chameleon changes color to blend into the background and spots enable a leopard to conceal itself in the undergrowth.
It is movement that usually betrays a predator. When an image flows across the light-sensitive cells in the retina, an alert response is triggered and sent to the brain.
|
 
 Send an Eek! insect E-card!
|
|||||||
But the dragonfly (Hemianax papuensis) gets its camouflage through mobility, the study said.
The insect shadows its target so precisely that it always appears as a fixed point in the prey's retina.
There is no optical flow across the prey's retinal cells, and so no alert response is triggered. The object is perceived by the prey as stationary and thus does not appear to be a threat.
The research was led by Akiko Mizutani of the Center for Visual Science at the Australian National University in Canberra.
His team used stereoscopic cameras to reconstruct the movements in three dimensions of 15 flights by male dragonflies that were jousting for territory.
"Stalker" dragonflies shadowed their targets with millimetric flying precision and positioning control, showing "clear evidence of active motion camouflage," the authors said.
Exactly how the dragonfly does this flying and navigational feat, though, remains a puzzle.
The scientists believe they did not see a simple case of insects chasing each other around. Quite often a "stalker" dragonfly would discreetly break away from his target and fly off, to ensure that he remained undetected.
< news main
