The Tribune - Spectrum


Sunday, April 15, 2001

They know how to entrap
By Nutan Shukla

THE tiny nymph of the assassin bug of Costa Rica is a tool-maker. It has a penchant for termites and has found a way of fooling the normally aggressive termite soldiers so that it can prey on termite workers, without coming to any harm. First, the nymph ‘dresses up’. It places small pieces of the termite nest on its body, which gives it the ‘scent’ of the colony. Thus disguised, it sidles up to the entrance of the nest and grabs the next termite that emerges, injects digestive enzymes into it and sucks it dry. It then uses the dried-out shell as a lure to catch more termites. Since nothing is ever wasted in a termite colony, certainly not the protein-rich skin of a dead corpse, that too is snatched from under the very noses of the soldiers. The bug has been seen to ‘angle’ for termites in this way for up to three hours, in which time it can catch as many as 30 i.e., one termite in every six minutes.

Another example of lure-using animals is the alligator-snapping turtle. It lies, partly buried, on the bed of slow-moving rivers in the eastern and south-eastern parts on North America. Only the head and open mouth protrudes from the river-bed. The sides, roof and floor of the mouth and most of the tongue are dark-coloured, but a small outgrowth on the tongue is conspicuous by its covering of red spots.

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The turtle can wriggle the outgrowth too, and to all intents and purposes it looks like a juice worm. Any small fish that comes to take the worm finds itself right in the turtle’s mouth. All the predator needs to do is snap its jaws shut and the prey is trapped.

A similar ploy has been developed by certain snakes. The young of deadly poisonous snakes such as the fer-de-lance, water moccasin and copperhead have yellow tips to their tails. If it is wiggled in front of a frog or toad, the movement attracts the amphibian within striking distance of the snake.

The most well-known lure in the animal kingdom must be that used by the angler fish. There are many species, some in coastal waters and others in the deep sea. Most familiar is the ‘monk-fish’, with its enormous, cavernous mouth. It lies very still on a sandy or muddy seabed, feathery outgrowths enabling it to blend in with the background.

On the front of its head, the first dorsal spine stands alone and has a fleshy tip. The fish can move the spine in such a way that the tip resembles a small, animate object worthy of investigation by a fish looking for a meal.

As soon as the prey is within a few inches of the angler’s snout, the mouth opens wide, the fish swallows violently and the prey is drawn in with the inrush of water. It all happens in an instant, backpointing teeth preventing the prey from escaping. Atlantic anglers can grow to 5.6 ft long and weigh up to 88lb (40 kg). The mouth of the Atlantic anglers is capable of taking conger eels, gurnards, rays and even diving birds. One greedy angler was once found dead, having choked on a gull.

The green heron not only uses tools but makes them as well. In order to entice a fish from cover and up to the surface, the heron throws out baits, much as a fly-fisherman would do. They might be live baits, such as insects, or artificial lures fashioned from twigs, feathers etc. If a twig is too long, the bird snaps it in two until it has sections of the correct length. These are scattered on the water and any fish that ventures into the open to eat the bait is grabbed instantly.

The black heron goes hunting with a sun visor. It darts about the shallows, stopping occasionally to peer into the water. As it does so, it fans open its wings and brings them up and over its head like a large, black, feathered parasol. It is thought that the wings shield the bird’s eyes from the sun and cut down reflections from the surface of the water.

In the tropics, the colourful frogfishes are relatives of the anglers and they adopt a similar strategy to fool prey. The lures often resemble a white or pink wriggling worm that coils and uncoils like out of its burrow.