Sunday, July 22, 2001		Nature

 The chameleon’s deadly weapon
Nutan Shukla

MANY predatory animals have a slow, stealthy approach ending with the sudden movement of some body part or other. Some of the outstanding examples are the tongue of the chameleon, frog and toad, mouth parts of a young dragonfly or nymph or the enormous mouth of many species of deep sea-dwelling angler fishes.

As far as the tongue is concerned, the chameleon has the ultimate weapon. Although the creature itself is very sluggish and slow, it is a very successful and efficient predator. Its turret-shaped eyes that can move independent of each other help the animal in locating the prey. While one eye is looking up, the other could be staring straight ahead or down, giving the owner of such a magnificent seeing apparatus the ability to look in each and every direction at the same time. If the prey is spotted, both eyes swivel rapidly to focus on the same spot, giving the animal stereoscopic vision with which it can not only accurately pinpoint the target but can also have the idea about the distance.

Without disturbing the victim, the chameleon opens its mouth slightly and the globular end of its pink tongue protrudes. In an instant, the prey disappears and the chameleon is chewing on its meal. The action is so fast we cannot see it. In a split second, the tongue is fired out of the mouth, extending to twice the length of the chameleon’s own body. They prey adheres to the sticky mucus at the tip, and equally quickly, the tongue and the food is retracted back into the mouth. In this way, one of the slowest creatures on earth makes one of the fastest movements.

Frogs and toads do not extend their jaws to gain an advantage, rather they too throw out their tongue. Most tongues are attached at the back of the mouth, but the frog or toad tongue is attached at the front. At rest, the top surface of the tongue is sticky while the underside is not. The speed with which it can use the weapon is phenomenal, beyond our normal perception and only visible to us with the help of high-speed cameras.

The frog sits and waits for an insect to settle. Triggered by the prey’s movement, the amphibian opens its mouth and the tongue is thrown out to twice its resting length. The sticky upper surface becomes the underside and lands on top of the prey. The insect sticks to the tongue and, like a piece of elastic, the tongue flies back into the mouth. All we perceive is an audible click, the insect disappears, followed by the frog making swallowing movements. The snatch takes just one-fifteenth of a second.

The dragonfly is an effective predator even as a youngster. The nymph stage is aquatic, and it is one of the most voracious freshwater killers. Its secret, like the John Dory, is in its jaws. The creature possesses a ‘mask’ (so-called because it masks the mouthparts), which consists of a lower jaw hinged to an upper jaw tipped with movable hooks. The whole structure can be extended in front of the nymph’s face and can capture anything from small fish to large tadpoles.