ART / Rainforest man: When Tony Foster scouts a location for one of his landscapes he can barely see the wood for the trees, the insects, and the charging pigs . . . Dalya Alberge reports

Before his first visit there in 1991, Tony Foster imagined the rainforests of Costa Rica would be rather like a David Attenborough nature programme: 'unbearably hot, humid, wet, muddy, bug-ridden, snake infested and dangerous. I expected my clothes and equipment to grow mould and rot. I expected to be occasionally extremely miserable and frightened'.

Right first time. Foster is a self-taught British artist and a hardened traveller who has walked hundreds of miles through the wilds of the Grand Canyon and Sierra Nevada to paint 'a celebration of the wilderness and the idea of a journey or series of journeys'. But the rainforests were something else. 'I've never been anywhere as uncomfortable . . . Everything rots, your clothes, your watch . . . even your belly-button.' During five months there painting large-scale watercolours he'd sometimes hallucinate about being back home in Cornwall, thousands of miles away from the heat-rash, the monotonous food ('rice and beans three times a day') and the insects . . . 'But you can't think about that too long. You acclimatise and adjust. Otherwise, it'd drive you mad.'

Nevertheless, he returned there yesterday, for a month's stay, to top up the number of paintings in his touring exhibition (now at the Exeter Royal Albert Memorial Museum) from 20 to 25, before the show hits San Francisco in June. There is no question of him painting from memory or photographs. 'I have to work on the spot. You couldn't write a diary six months later. It would be stilted.'

His watercolours are rather like an illustrated diary: his realist images, which convey the claustrophobic beauty of the forests, are presented with a short text that forms part of the composition. Shorthand notes, rather like those in the more conceptual work of Richard Long, appear alongside the landscapes: for example, next to his image of the Monteverde Cloudforest, he records carrying the food and equipment needed for nine days, the Volcan Arenal that erupts throughout the night, and his first conversation for four days when Canadian biologists arrive. Interspersed with the text are small studies of the lizards and birds encountered on route.

His journey begins with a flight (from Houston to San Jose), then 'a bus, then a horse and then slower and slower transport'. He is heading for a cabin probably three days' walk from the nearest sign of civilisation. The cabin is designed for forest workers who patrol the area for illegal gold prospectors and poachers. The workers, who were initially hostile, have become useful contacts: apart from offering food, company and accommodation, they also suggest spots to paint.

If he's really unlucky, they offer to take him there. 'They're so incredibly fit, travelling through the forests with only a machete, a gun and a bag of coffee, they speed off like a rocket. I am loaded down with my equipment, panting away. In half an hour, they're out of sight. I'd have to say, 'See you in two days'. They'd draw maps for me, but they could never understand why I should get lost. 'Why should you?' they'd ask. 'If you keep this mountain in front of you . . .' ' Maps don't help much. To Foster 'they're just green splodges of trees and contour lines'. Getting lost is an occupational hazard.

Once he is back in the romantic wilds of the cloud-forests, he will spend two or three days just walking, taking in the landscape, before rooting himself to a chosen spot for perhaps ten days. He has with him a folding drawing-board which he props up with twigs (from a dead tree, he hastens to add). Easels are too cumbersome. Likewise, any medium but watercolour. 'Watercolour is more portable. I couldn't use oil. Apart from the equipment needed, you'd have flies stuck to it. And it has to dry before you can carry it and that would take days'. Instead, he has a paint- box, just four by three inches (he doesn't need anything larger: 'The colours I use are very intense'). He doesn't have to worry about water for paint: it rains constantly (an umbrella is as essential as a paint brush).

Humidity makes working-conditions tough. It impregnates the paper, making it impossible to mop off mistakes. Often, the paper is so wet a pencil leaves only a dent. Paper is the only thing that doesn't turn mouldy ('Even the paint in the box grows a green mould'). Then there are the insects. 'You're constantly bitten . . . by so many different things.'

Scorpions are particularly dangerous ('They're quick on the draw'), but they make good subjects: he painted one that had wandered on to his dinner-plate by candlelight, likewise a Blaberus giganticus, a four-inch- long cockroach with transparent back. 'It was nauseous in some ways, beautiful in others.' The artist has had run-ins with monkeys, who bombard him with twigs and cashew-nuts to drive him from their territory; peccaries - wild pigs about two or three foot high - charge making an aggressive clattering noise with their clapping jaws (advice in the region is 'run up a tree' if they approach). And, most dangerous of all, are the encounters with snakes. The Costa Rican rainforest is home to a particularly aggressive species, the fer de lance which, unlike some snakes, gives chase to humans and is extremely well-camouflaged and hard to spot. Better by far, for art and well-being, is a (well-fed) boa constrictor: Foster once found a nine-foot-long specimen, as wide as a man's thigh, which remained coiled and motionless for three days, as if posing for its portrait. Scientists working nearby assured Foster that as it had already eaten, it would not move.

Although some of his images of insects and reptiles are presented almost clinically, laid out individually on a white sheet, his approach is entirely non-scientific. 'Scientists find that a bit baffling. They come rushing over with a plant specimen that they think is really interesting but which, as far as I am concerned, is dull to paint. I'll show them something I think is really interesting and they'll say, 'but those are really common.' '

He never paints the animals or reptiles he sees in their natural habitat. 'Such pictures always verge on cliche. My paintings of the forest are a distillation of what I've seen over days. If I stuck animals into them, perhaps a swinging monkey, you'd be looking at the forest during a tenth of a second. Animals are so well camouflaged, you can hardly see them anyway.'

All his trips are financed from the sale of paintings, which go for between pounds 450 and pounds 10,000. (Three months in the rainforests, including flight and equipment, cost him up to pounds 3,000.) Although he has had numerous one-man shows in British public galleries, his market is established in America; one of his most ardent collectors is Paul Mellon. His choice of subject - the Americas - probably limits his buyers. 'The United States has thousands of miles of pristine wilderness, which they vigorously protect; in Britain, we have tiny patches, forgotten bits . . . that no one can think of making money out of.'

Foster repudiates any suggestion that he may be jumping on the eco-bandwagon. 'Artists have been going to the rainforests since the 19th century. Darwin was accompanied by an artist. Every generation thinks they've discovered it. I chose to go there as I wanted a complete contrast to the subject of my previous exhibition - the huge, arid desert of the Grand Canyon.' He is doing his bit to protect a part of the world that needs urgent protection: he is donating a percentage of his income towards buying up areas of primary rainforest which, he confirms, 'is being felled at an alarming rate. You see trucks carrying the forest away. It's terrifying.' A small painting buys one acre; a large one saves five.

Royal Albert Memorial Museum, Exeter (0392 265858) To 20 Mar; Terrace Gallery, Harewood House, Leeds (0532 886213) 3 April-16 May.

(Photograph omitted)