Sunday, April 1, 2001		Nature

INSECT stings are dangerous, not for a healthy adult but for those suffering a weak heart or prone to strong, allergic reactions. For prey animals, an insect sting is always deadly. Some stinging insects even have the capacity to inflict lasting damage. According to an estimate, there are more human deaths from stings of wasps, scorpions and bee and snake and spider bites, than there are from attacks by sharks.

Parasitic species of wasps, like the digger-wasps of Arizona, are dangerous for large spiders. In the struggle between the two insects, which is usually one-sided, the winged insect due to its agility is able to out-manoeuvre and overpower the large, hairy tarantula spider. The wasp avoids the spider’s formidable, poisonous fangs and stabs it with its stings. The spider is not killed but paralysed. It becomes a living food store for the wasp’s offspring. She lays her eggs inside the spider and when they hatch they eat the spider’s body from the inside out.

Spiders themselves are venomous. Notorious black widows are the most dangerous to man, which accounted for 55 deaths in the USA before an antivenom vaccine was developed. The spider does not deliberately bite people; it is the only way it knows of defending itself, but in its more natural encounters the spider purposely subdues or kills its prey with poison. A spider stabs at its victim with a pair of large, sharp, hollow fangs. Having incapacitated its victim, it does not slice up the body and swallow it; rather it pierces the skin and sucks out the body fluids.

Centipedes also have a poisonous bite. Hollow, fang-like claws at the front and are fed by ducts from special venom glands. The victim is grasped, injected and paralysed, and then sliced up by the jaws. Large species have enormous fangs and will lie in wait below stones and undergrowth for lizards, frogs, toads and even mice. The larger tropical species have a painful bite than can be dangerous man.

Two species of lizards — the gila monster of Arizona and the beaded lizards of Mexico’s Sonoran Desert — have venom glands in the lower jaw. The glands consist of three or four lobes each and have a duct that runs to the base of the large teeth, which have grooves along which the poison can flow.

Snakes have paired fangs in the upper jaw with which they deliver their venom. Some snakes have fangs at the back of the mouth and they tend to chew on a victim in order to inject the venom. The venom is produced by modified salivary glands and is delivered along a groove in the fangs. Other snakes have large, hollow, tubular fangs at the front of the upper jaw. Cobras and mambas have fangs which are permanently erect and ready for stabbing a victim, whereas rattlesnakes and vipers have their fangs folded back into the roof of the mouth when resting and only bring them out at the moment of biting.

The most formidable poisonous serpent in the world must be the king cobra, which can reach six metres in length. It feeds mainly on other snakes, but has been known to attack and kill an elephant in self-defence. One of the most deadly venomous snakes to man is considered to be the taipan of Australia. This three metre-long brown snake, the longest of Australia’s poisonous snakes, manufactures huge volumes of highly toxic venom. An individual was once ‘milked’ and delivered a cupful of poison, enough to kill tens of thousands of mice. The fangs are longer than in most snakes, and so the taipan can inject its lethal brew deep into the body of its victim. Instead of a single strike and grasp, the snake strikes repeatedly at the prey. Death for the unfortunate small mammal or bird is instantaneous.

One curious and rare small mammal has a poisonous bite. It is the squirrel-sized, shrew-like solendon of the West Indies. There are two species — the agouti of Haiti and almiqui of Cuba — and both have a long, trunk-like snout. The poison is in the saliva. Shrews have a similar toxic Saliva.