Soft Toy

Our bodies are built around the supporting framework provided by our skeletons, and none of our bones is visible. But there are creatures whose skeleton is quite visible because it is found outside them. Such a skeleton is called an exoskeleton and forms a sort of suit of armour for its possessor. The number of living things getting their shape and protection from exoskeletons is very large?for it encompasses that huge group of animals called arthropods, including spiders, millipedes, bugs and crabs.

The skeletons of humans and most vertebrate animals are made up of bone and cartilage (the exceptions are fish such as sharks, which possess a skeleton made entirely of cartilage). The exoskeleton of any arthropod, in contrast, is made of chitin, a substance which exists in two forms: hardened and not hardened. The first form is rigid, the latter is flexible. This allows the skeleton of, say, an ant to be made entirely of chitin and yet have flexible joints: the joints are made of chitin that is not hardened.

An exoskeleton, made of hollow tubes and plates, is lightweight and strong. But if a wasp, for example, were to be much larger, say as big as a dog, the exoskeleton in its present form would not do. It would need to be much thicker and therefore heavier. The dog sized wasp would wear a very cumbersome skeleton indeed?a skeleton so clunky that the wasp would not be able to get about. This is perhaps fortunate for us! An exoskeleton is a bit of a nuisance when its owner is growing in size. Periodically, it must be shed. The new skeleton is not hard to begin with, and the animal ?inflates?. This ?soft? stage is a very vulnerable time and calls for retirement to a quiet corner until the skeleton hardens.

A hard exoskeleton is a good thing to have if you fancy the shiny, metallic look, such as sported by vast numbers of beetles. But if you want to be furry and soft, an exoskeleton is not for you. Have you ever heard of a cute and cuddly insect? As a matter of fact, there is one arthropod that has a furry and attractive appearance: the velvet mite (see cover photograph). Its body is covered with tiny ?hairs?, making it as soft as it looks. Unlike some of its close relatives, this creature poses no threat to you at all; it is an eater of small insects, and is so shy that it curls up into a ball most readily. Indeed, it is almost as inoffensive as a stuffed toy.

Kumaran Sathasivam
Madras
22 January 2008