Rats - we love them or hate them. The Lord Buddha is said to have charged rats with bringing about the end of the world. After spiders and snakes, they are the pest that humans like least - no wonder rat extermination is big business! Yet rats are among the most popular animals sold in pet shops.

But how can rats be so well-loved and - at the same time - so feared? How you feel about a rat may depend on what kind of rat you are talking about and where you see it. Watching one play in a cage in someone’s house is one thing, seeing it scuttling through a dark alley is quite another.

First know your rodent...

If you don’t believe that, then let me introduce you to Fingers the brown rat. He and his fellow brown rats often feature in the Animals in Action displays at London Zoo and are very popular. Perhaps it is their twinkly eyes, twitching noses and whiskers, and soft furry coats that make people like rats once they get to know them.

Fingers got his name because of a disfigured claw. He is small for a brown rat, 28cm (11in) long (as a rule, brown rats are a few inches bigger than black rats). Fingers eats sunflower seeds, nuts, fruit and vegetables and he loves cheese.

He even takes a rodent pellet daily, which helps keep his teeth trimmed and contains vitamins and minerals. He also likes special treats. His favourite is a mealworm larva - the big tropical kind. But Fingers has to watch his weight - he weighs 408 grams and is weighed every morning. If he eats too much, he won’t show his usual rat-like behaviour.

Fingers sleeps in a cardboard box with the other brown rats. They make beds from torn up newspaper and hay (they are warm-blooded, so need to keep warm during the cold night hours).

On a normal day, Fingers is woken at 9am and he is weighed. He returns to his box until midday, when he is collected for the Animals in Action displays. The shows last 30 minutes, although the animals don’t work the whole time. There are usually four types of animal in a show. Fingers has food after each performance. Like all rats, he needs a steady supply of water, which is why wild rats in towns tend to live in places like sewers.

After the first display, the rats have a sleep until being woken for the next show, usually at 3.30pm.

The zoo-keepers leave in the late afternoon. As nocturnal creatures rats probably spend the night-time hours exploring their habitat.

...inside out Now that you’ve met Fingers, let’s go inside a rat and find out how they work.

Like humans, they are boned animals and have the same basic vertebrate pattern - a skull and backbone, ribs, two bony rings or girdles (like our shoulders and hips) and four limbs. Inside, their organs are arranged much like ours.

Rats, like us, are mammals - we share things like fur, ear flaps, nipples (the mothers feed their babies on milk) and the young are born alive, having been “grown” inside the mother (not in an egg outside the mother’s body like birds and reptiles).

Mammals have one bone in the lower jaw and two sets of different kinds of teeth. Both rats and humans have a diaphragm dividing the body cavity into two and used in breathing movements. And we both have a tail: a rat’s is more noticeable; people just have a few tail bones in their lower backs.

One difference is that rats belong to a big group of mammals - rodents. More than 40 per cent of mammals belong to this group, which are gnawers (the name comes from the Latin rodere - to gnaw).Rats have specialised gnawing teeth at the front, which are bright orange. They have relatively unspecialised hands and feet but have sharp claws, while our nails are flat and broad.

Life for a rat is a matter of following one’s nose - smell is a rat’s calling card. One rat can tell the sex and social standing of another simply by its smell, and they can identify precisely which rat made it. Baby rats can recognise their siblings by smell, even if raised in a different litter. They make meticulous parents and communicate by squeaks and grunts.

Wild rats have more babies per birth than humans - as many as eight pups are in each litter.

In a good year, a female rat can breed every four weeks. The babies take three weeks to develop before they are born.

Rats spend most of their time sleeping. When awake they are feeding or washing! They spend 50 per cent of their waking time washing. Their food tastes are wide - wild rats will eat anything that can be digested.

They have to care for their teeth, which they do by gnawing grain or wood. If they don’t, their big orange front teeth grow round and penetrate their lower jaw, so they can’t eat and they die. Unlike our teeth, these two keep on growing.

So there you have it - the inside story of a rat. Next time you see one, remember they are just our fellow inhabitants of this great big world that we share. Happy rat spotting!

Dr Sue Dale Tunnicliffe is a researcher at Homerton College, Cambridge

Rat facts

* As with humans, what goes in must come out. Zoo rats produce about 10 to 15 faeces a day, which look like dark brown pellets about 1cm long. This is undigested food and waste from the gut. The colour comes from the waste products of old red blood cells. In the wild, rats produce about 40 droppings a day, which is one-tenth of their body weight. Rats urinate a great deal, but in small dribbles, a bit like dogs.

* It’s estimated there is one wild rat for every human in the country, and they are on the increase. Town rats like sewers and drains. Country-dwelling brown rats live in earth burrows and are good diggers.

* Wild rats live for about a year. Tame rats can live for up to five years, although two-and-a-half to three is more likely.

* Rats are so intelligent that many biologists think they could become the dominant animal in the world should something - such as a nuclear incident - obliterate humanity. They can survive nuclear disasters unscathed without genetic mutations.

Rat history

* Rats first reached our country on ships. There are two species of rat that live wild in the UK, the brown rat, Rattus norvegicus, and the rarer black rat, Rattus rattus, which lives near ports.

* Like rabbits, Rattus rattus arrived in Britain with the Romans. The brown rat arrived in the 1720s and spread rapidly, taking over territories where the black rats live so that now there are few of them left.

* Rattus rattus, the black rat, is one of the rarest animals in Britain, yet it is officially classed as a pest.

* Black rats are often blamed for spreading the Black Death - plague - by carrying fleas that spread the disease to the human population of Europe in the 14th century. The plague reached England in 1348 and killed between one-third and one-half of the population in a few months.

For details of the Animals in Action displays at London Zoo, call 0171-449 6552.