He stood in his black tunic, bare-legged, with the hardened, spatulate feet of one used to rough living. From beneath the sleeves of his kushma protruded bundles of fragrant charapuñamemba leaves. Rows of tiny gold and coloured beads circled his neck. On his chest, a long string of peccary and jaguar teeth jaggedly proclaimed his prowess as a hunter. Parrot feathers speared his nose and earlobes. His crown, a multi-coloured flurry of toucan, macaw and humming-bird plumes, cascaded down his back beneath an iridescent band of green and blue beetle wings. He looked splendid.

Anastasio is an elder of the Cofán, one of the smallest of the five indigenous groups that live in the Cuyabeno Reserve - 650,000 hectares of virgin rainforest deep in the heart of the Ecuadorian jungle.

No theme park, this. It had taken us six steaming and juddering hours from Quito by plane, bus and powerboat to reach this untouched corner of the world. We had slalomed for three hours across the bubbling brown waters of the Aguarico river, avoiding the submerged trees and shallows of the dry season: 120km of snaking brown bordered by dense, relentless, hypnotic green, to our "hotel" - a converted river boat; a haven with a bar and cold beer.

We gathered round in the 40C heat, sweltering and ridiculous in protective long trousers and gumboots while Anastasio anointed us, Indian-style, with decorative red dye from the atoche plant. Thus prepared for our jungle trek, we set off, Anastasio pausing to collect a machete and replace his head-dress with a filthy Nike baseball cap.

Not for the first time, I wondered what an arachnophobe such as myself (phobe, for that matter, of all things creeping or slithering) was doing in a jungle. There is, after all, little to do here other than admire nature in her miraculous diversity. I thought of the deadly f er de lance and coral snakes (hence, the wellies); of the tree boas that lie camouflaged in the branches and drop on to their prey . . .

Too late: we were already beneath the thick green canopy that dulled the sun, gingerly picking our way in single file through the tangle of roots, stepping over fallen trees, avoiding towering termite nests and trailing lianas, and pausing to give right of way to the serried ranks of leaf-cutter ants that marched beneath their green parasols with military discipline.

Jaguars were sighted seven times here in the last year. More commonly, this is the stomping ground of the world's largest rodent, the capybara, as well as monkeys, tapir, armadillo and peccary (a local version of wild boar with inverted incisors), which are hunted for food.

Anastasio showed us the canalete tree, from which blowpipes are made. Soon, he stopped again, hacking with his machete at a palm which, within seconds, he had whittled down to a needle-fine dart. The reddish bark of a nearby tree yielded curare, the poison with which the dart would be tipped. But, explained Anastasio with his gappy grin, it takes a lot of puff to kill a monkey at 50 metres with a 2m blow pipe. Training is required. So at 14, boys are taken into the forest and made to gorge on emetic plants. Vomiting, we are told, strengthens the diaphragm. Overhead, squirrel monkeys screeched on cue, and a pair of macaws took flight.

The multifarious uses to which flora is put is a revelation - from clothing and household utensils to medicine. To the unearthly ostinato of screaming pihas and howler monkeys, Anastasio pointed out some of the 2,500 species of curative plants - among these, cordia nodosa , which when boiled makes an all-purpose anti-snake-bite serum, brownea, which is used as a contraceptive, and the pungent bark of a tree that saved the Cofans from a measles epidemic brought by missionaries.

We stopped beneath a massive capok tree, whose roots are considered the home of the Gods. Here the shamans come to take the hallucinogenic ayahuasca and consort with the spirits. It is also the home of the devil Cocuya and children are warned to keep away.

Anastasio told us how two of his grandchildren ventured too close to the capok and were found dead. He shrugged philosophically: "Cocuya took them." So much for the teaching of the missionaries.

T here are 526 species of birds in the Napo basin alone. The best way to spot them is by floating silently down-river, neck craned heavenward. Silvestro, an Indian of the Quichua tribe sporting a T-shirt with the legend "Death Ride", was to be our guide through the dappled backwaters of the Cuyabeno, beneath which lurk cayman, sting-ray and piranha. We transferred to his catamaran: two dug-out canoes ingeniously joined by rows of benches, and propelled by his four daughters, an apocalyptic paddle at each point of our craft.

As we floated through the reflected trees the only sounds were those of our own ripples, the distinctive glissando of the oropendola bird and Silvestro's shrieks of excitement as he spotted a rare harpy eagle. A balletic school of pink dolphin accompanied us into a tranquil pool, at which Silvestro's four daughters suddenly jumped overboard, leaving us rudderless. Come and swim, they said, the water's lovely. Oh, and by the way, this is the Lagoon of the Anacondas . . .

It doesn't come much wilder than this; not with hot-and-cold running water, anyway. Safely back on our floating hotel as the light began to fade, the barman prepared a mosquito-repelling cocktail of pisco sour, and the insects prepared to burst into their nocturnal song. Their sounds were so beautiful that even I began to look forward to this nightly eruption of bug life. As aversion therapy goes, I would count this a major success.