It is 6.00am, and we are awoken by the raucous echoing call of a troop of howler monkeys. They are perhaps 2 km away, but the sound fills the forest around us. Dawn is just breaking as we venture along a trail through the primary rainforest. Mysterious shapes flit around us. I note where they have settled, but they are almost impossible to see. These are Satyrine butterflies - some, like Taygetis angulosa, look exactly like dead leaves. Others like Haetera piera are almost entirely transparent.

Enormous Caligo Owl butterflies flit from one tree trunk to another. Their wings have a feathery appearance, and are marked with false "owl's eyes", enough to startle any predatory bird, and give the butterfly a chance to escape. Every butterfly species here has it's own distinct personality. They taunt you. The zebra-striped Colobura dirce sits motionless on tree trunks as it feeds at sap runs, but when disturbed, instead of taking flight it scuttles around to hide on the opposite side of the tree. The hairstreak Arawacus aetolus sits facing sideways on a leaf, but as soon as you get within a metre, it turns to show you it's posterior ! Other butterflies such as the Eurybia Riodinids, and the Nascus skippers, hide under leaves, darting out periodically to investigate intruders before disappearing again beneath another nearby leaf.

The muddy soil in the glade is carpeted with butterflies which are imbibing the mineral-rich moisture. There are so many butterflies here that it is impossible to walk without treading on them. Amongst them are brilliant metallic green Caria Metalmarks, black and orange Riodina, red Marpesia Daggerwings, and the stunning purple Rhetus periander. At the edge of the glade we watch a Starry Night, Hamadryas velutina, basking head-downwards on a tree trunk. This is perhaps the most beautiful butterfly we see today, its large velvety black wings adorned with hundreds of glimmering blue spots.

11.00am - It is hot now, and the forest resounds with the call of giant cicadas. The sound begins as a slow hesitant clicking, gradually accelerates to a rattle, then a hum, and finally becomes a haunting siren wail which fills the air for a few moments before fading into silence.

In the afternoon we travel upriver by dugout canoe. Amazon kingfishers swoop past, a harpy eagle hovers high in the sky above us. On a nearby rocky island we see a caiman basking, and along the riverbanks we see sun bitterns and the very beautiful capped heron. Bright yellow Phoebis butterflies fly in follow-the-leader fashion along the river's edge, stopping at mineral rich sandbanks to imbibe moisture. Sometimes hundreds settle together on the ground, erupting into flight as we approach.

We stop at various places to explore the trails. Imaginary snakes wait to strike from behind every tree - but they are not all imaginary. Clambering up a riverbank we are suddenly confronted by an enormous anaconda, perhaps 8 metres or more in length. Luckily for us it has already eaten - it's belly greatly distended by the capybara which became it's breakfast !

As the day cools down, we journey back along the river. Beautiful birds fly across our path - green ibis, ringed kingfisher, striated heron, kiskadee, paradise jacamar. A giant river otter inquisitively pops it's head out of the water next to the boat. A capybara, looking like an enormous guinea pig, looks across at us from the riverbank. During the next half hour we see a dozen tapirs, amongst the most enchanting and gentle of all animals, emerging from the forest at different spots along the river.

Back at our base the light is fading fast, and the howler monkeys roar again. We sit down for our evening meal, comparing notes about the wonders we have seen, and agree that this is probably the most wonderful place on Earth.

The next morning we travel downstream for an hour, disembark from our dugout, and get into a jeep. We leave behind the beautiful pristine rainforest, travelling through secondary forest, and then for several miles through cattle pastures, until we come to the town where we catch a plane to our next destination.

For 4 hours we fly across what was formerly rainforest, but all we see is semi-desert. The forest has all been burnt down and turned into cattle pasture, but the pasture only lasts for a few years, and all that remains now is a barren dusty landscape dotted with termite mounds. Looking down from our plane we see a dead parched world, devoid of life.

We have been told that our next destination is an oasis - an "island" of rainforest that has miraculously survived amidst a desert of failed cattle ranches. Our plane lands and we board a charter bus. For the next 5 hours we are driven across 200 miles of devastated land. The forest has gone, the cattle ranches have failed, and the air is dry and dusty.

By the time we arrive at our base, we have a feeling of the most intense grief. Many of us, all grown men, are close to tears. We have left the most wonderful and precious environment imaginable, and now realise the full horror of what is happening in Brazil. The air around us is thick with smoke, our eyes are watering, and we are struggling to breathe.

The spot where we are now standing was once the richest butterfly site known on Earth. Just 20 years ago it supported over 1500 butterfly species, but now they are very scarce, and within 5 years will almost certainly be lost forever. For 4 days we search the tiny fragment of forest that still remains here, looking in vain for butterflies, muttering in disbelief at what has happened here.

The Amazon, the lungs of the world, is dying from cancer.