Extreme Nature. Mark Carwardine
one reason why their heads are shaped in the curious way they are.
Sharks have special electrical receptors – hundreds of tiny, dark pores called ‘ampullae of Lorenzini’ – which are filled with a conductive gel that transfers electrical impulses to a nerve end in each pore. Ordinary sharks have these all over the snout and lower jaw, forming a curious pattern of dark holes resembling a sparse five-o’clock shadow.
But hammerheads also have a mass of them across the underside of their oblong heads, which scan across the sandy sea-bottom like metal detectors, searching for prey animals that can’t be found in any other way – creatures such as stingrays and flatfish that bury themselves, lie still and usually have no appreciable scent.
The hammerheads are able to detect the slight direct currents caused by interaction between the bodies of their prey and the seawater and the even slighter alternating currents caused by muscle contractions around an animal’s heart. The eight species of hammerhead can sense it better than most other sharks, and the biggest of these, the great hammerhead, which measures up to 6m (20ft) long, may be able to sense it best of all.
| NAME | holy-cross, crucifix or Catholic toad Notaden bennetti |
| LOCATION | Australia |
| ABILITY | producing a super ‘superglue’ |
© Ken Griffiths/ANTphoto.com
Some of the world’s strangest creatures are found in Australia – a continent of extremes giving rise to extreme adaptations. The holy-cross toad lives where many other amphibians can’t: in hot, harsh areas inland, where droughts may last for several years. It uses its strong back legs to burrow down in the soil, where it sits out the heat of the day, and when drought sets in, it survives by digging a chamber a metre or so underground in which it aestivates (becomes dormant), emerging only when the rains return.
Like its close toad relatives, the holy-cross also has unique glands in its skin. If it is disturbed or distressed, these release a special secretion that turns into glue. The glue hardens in seconds and has a tensile strength five times that of other natural glues. This is particularly useful should ants attack, as even the biggest immediately get stuck to the toad’s skin. And since, like all frogs and toads, it sheds its skin and eats it about once a week, the holy-cross toad has the pleasure of swallowing the ants that attack it.
Scientists in Australia are now trying to produce an artificial glue as good as the toad’s. Holy-cross toad glue will stick plastic, glass, cardboard and even metal together. More importantly, it can repair splits in cartilage and other body tissues and therefore might prove to be a miracle adhesive that will help surgeons repair the most difficult of injuries.
| NAME | castor bean Ricinus communis |
| LOCATION | worldwide; origin unknown, but probably Ethiopia |
| ABILITY | producing the deadly poison ricin |
© Haroldo Palo Jr/NHPA
The castor bean plant produces possibly the most deadly plant toxin, 6,000 times more deadly than cyanide, but it has also been known for thousands of years as a wonder plant. The secret and the poison both lie in the seed. More than 50 per cent of it comprises a rich oil, but to protect it from being eaten is ricin, a protein toxic to almost all animals (lesser quantities of ricin occur in the leaves). The poison, once ingested, inactivates the key protein-making elements of a cell without which it can’t maintain itself and dies.
For humans, death is prolonged, ending in convulsions and failure of the liver and other organs. There is no known antidote. The most usual cause of poisoning comes from accidentally eating seeds, but ricin can be administered in aerosol form, in food or water, or injected, as in the famous case of a dissident Bulgarian journalist. While waiting at a bus stop at Waterloo station in London, in 1978, Georgi Markov was murdered by being stabbed with an umbrella that injected a pellet containing ricin. Widely available and easily produced, ricin could be used for biological warfare.
It is equally easy to extract the seed’s valuable oil, however, which has been used for at least 4,000 years as a lamp oil and soap and also as medicine for a huge array of ailments. Today its uses include high-grade lubricants, textile dyes, printing ink, waxes, polishes, candles and crayons. In the future, its array of protective chemicals may even provide a cure for tumours.
| NAME | Amazon leech Haementeria ghilianii |
| LOCATION | Amazon basin |
| ABILITY | drinking up to four times its weight in blood |
© Werner A Wuttke
No, the biggest blood-sucker isn’t a vampire bat. Vampires, which are native to the tropical Americas, don’t actually suck blood – they lap it up. They find large mammals – most noticeably cows, pigs or horses – make a cut in their skin and then drink the blood. Not being very big (average body length is 6.5–9cm/2.5–3.5in), a single bat only actually consumes a few tablespoons of blood a night, though because of the anticoagulant in its saliva, the prey keeps bleeding for some time after the bat has flown away.
The world’s largest leech, measuring up to 46cm (18ins) does suck blood, however, and a very hungry one can take in four times its body weight before it becomes satiated. Since a large Amazon leech weighs about 50g (1.8oz) – the record is 80g (2.8oz) – that’s a lot more than a few teaspoons of blood. Like the vampire, the Amazon leech feeds on large mammals, which it attacks when they enter water, and it also uses an anticoagulant to keep the animal’s blood flowing. But the leech injects an anaesthetic, too, so that the temporary host is unaware of what’s happening to it.
All leeches are segmented worms – their nearest relatives are earthworms – and all, regardless of size, have precisely 32 segments. A few segments at each end of the Amazon leech are modified into suckers for attaching to prey, and every segment has its own independent nerve centre – hence a leech has 32 brains.
| NAME | polyphemus moth Antheraea polyphemus |
| LOCATION | North America |
| ABILITY | a male can detect a female on the evidence of just one molecule |
© Jeff Lepore/Science Photo Library
Many animals rely on their sense of smell to find food or a mate and even to find their way around. Some live in places where other senses are of little use – eyes don’t help much if you spend most of your life in the dark, and ears would be hopeless in a particularly noisy environment – so they rely on smell more than most.
Some animals, such as sharks, are selective in their smelling abilities and are super-sensitive to significant smells that are relevant to activities such as feeding or breeding. In fact, smell is so important to sharks that they have been dubbed ‘swimming noses’. Their smell receptors are fine-tuned to picking up small concentrations of fish extract, blood and other chemicals