The Ark Files - Spiky Animals

Being spiky is a definite advantage to an animal. Spines can be used for defence or offence, for burrowing, bouncing or even getting a drink.

Spinning pin-cushions

Encased in long, movable spines, sea urchins travel fearlessly over rock platforms, grazing on algae. Some species that live on the sandy shores have become burrowers. With shorter and denser spines than those that live along the rocky shores, these particular urchins can dig themselves rapidly into the sand, spinning their short spines on ball-and-socket joints, spraying sand as they dig and looking just like midget harvesters.

One species of tropical sea urchin has long, hollow spines which it tilts and waves at intruders. The spines are encircled with barbs and tipped with poison. Handling or stepping upon this urchin is definitely not a pleasant experience!

A prickly issue

The Australian ant-eater or echidna (which means 'spiny one') is well named: its back is armed with many long spines surrounded by bristly hairs. If threatened it will protect itself by digging quickly and with great gusto until very soon all that is left above ground is a mound of spines.

There is a drawback, however, in having a body covered in spikes. The echidna, an egg-laying mammal, carries her babies in a temporary pouch. When the babies are about seven weeks old and 10cm long, they start to grow their spines, and at this point their mother has to push her prickly youngsters out. She continues to look after them for a few more weeks while their spines keep growing but they are definitely banned from her pouch!

Get the point?

Porcupines are quite different. They have more hair on their bodies and their quills (made from fused bristles) can be up to 13cm long. These quills are very sharp with barbed tips and can thus do a fair bit of damage.

The African Porcupine can be quite aggressive. Although slow moving and good at climbing trees to escape predators, it needs to be approached with caution. If challenged on the ground, a porcupine will swing its tail where the largest, most dangerous quills are, releasing them into the face and body of its attacker and causing painful wounds and festering punctures. Apparently more lions in the African Savannah are killed by infections from porcupine quills than anything else!

Sharp talk

The hedgehog is also covered in spines and, like the echidna, its spines are deeply embedded in thick skin and don't easily come out. When it senses danger, the hedgehog rolls into a tight ball with all its spines sticking out. It will also hiss and chuff, shudder and jerk. When touched, the hedgehog jumps upwards or charges forwards a few centimetres, driving its spines into the skin of its attacker. But this rarely does any serious damage.

Only three centimetres long, a hedgehog's spines are very strong, hard to break and well-anchored. This allows the hedgehog, which is a very poor climber, to fall from a serious height, bounce on its spines and amble off unharmed.

A hard act to swallow

The Thorny Devil is a very small, weird-looking creature that eats only ants and lives in the deserts of central Australia. Each of the protective scales that cover its body is shaped like a thorn. Apart from giving this tiny lizard a fearsome appearance, these thorns are also an excellent defence as there aren't many birds willing to risk swallowing them.

The Thorny Devil's pointy scales can also function as straws - very useful in the desert. Each scale has a thin groove starting at the tip of the thorn. In the cooler nights the dew collects in these grooves and is drawn down along the lizard's back, like a straw, till the water reaches its mouth.

Sorry, not on the menu

The Porcupine Puffer fish is a most unusual looking animal with a large head, fused front teeth, eyes like big green marbles, and a squarish, yellow body covered in poisonous spines. Even more unusual is its method of scaring other fish away. If approached it will gulp down mouthfuls of water, pumping itself up till it resembles an unappetising prickly balloon, too large to fit into a predator's mouth. If caught unawares, it can blow itself up in the fish's mouth to a size impossible to swallow, whereupon both fish will die.

The flesh of the Porcupine Puffer fish is also fatally poisonous but, strangely enough, is considered a delicacy in Japan where, despite precautions, as many as 100 deaths a year occur in gourmet restaurants.