We were already deep in the Amazonian rainforest, in the borderland between Peru and Brazil, based in a camp somewhere along an unnamed tributary of another tributary of the Rio Javari that marks the border, and that morning we rose early to travel by canoe yet deeper into the forest.  Local hunter Alejandro had encountered a large adult anaconda and was willing to take us there.

He'd seen the snake in a pool on an island that barely bulged above the swampy waterline, so we’d been warned to wear rubber boots. Mine are tight, sweaty things that chafe, and the second I was settled I wrestled them off, rocking the canoe. Alejandro spat out the remains of his hand-rolled cigarette and picked up a paddle.

A quarter of an hour upstream of our camp, he manoeuvred us into a narrow channel between low-hanging branches and submerged trees. As our canoe threaded its way through dozens of similar skeins of anonymous vegetation, I knew that I would never be able to find my way out if Alejandro weren’t with us.

Our canoe turned, reversed, and turned again as he pushed us off flat river-bottoms or away from impassable trees. All I did was duck and warn the others when branches threatened to whip us in the face. I was at the front, camera ready, waiting to emerge onto wider water and hoping for an image that would take my mind off the humidity and the buzzing insects. The most likely photo, assuming I got lucky at all, would be a bird roosting in a distant branch, but you can never predict what the rainforest will bring. Days earlier, walking at night upstream in the Colombian Amazon, I’d been rewarded with an amazing picture of a sloth that had climbed down to the ground. Only yards away, pale against the dark forest, it had stared at us with an intensity that probably mirrored my own. I’ve seen sloths before but never in the wild, and I won’t need the photo to recall my exhilaration of the unexpected, fortuitous encounter.

I fantasized of course of ripples in the water, a giant caiman or an anaconda, an open-jawed, photogenic attack, an adventure. However, there was nothing in the water beyond leaves and bobbing fallen tree-fruit. Despite the ever-present bugs who’d been gorging themselves fat and delicious on my blood, I didn’t see a single bird among the branches.

There were four of us in the boat. My friend Ben – as lost as I – the cheerful Tikuna guide Carlos, who had been in this part of the rainforest before but whose ancestral territory was miles away on another river, and Alejandro, whose silence spoke to me of a man accustomed to being alone in the forest. I imagined something befalling Alejandro and wondered whether Carlos would be able to get us out of the swamp and back to camp. Otherwise, I decided, we’d have no option but to hope that the slow current would direct our canoe out of this submerged forest into a larger flow that should eventually pass a settlement.

Of course, I knew that of all of us, Alejandro was the least likely to get into trouble. In any ranking, I’d probably be on the front page of that list. Inspired in part by a great-uncle who led expeditions to other rainforests, I’ve been to remote parts of the world. I’ve even had experience of helping conservation scientists monitor monkey populations in the Amazon, but I’m a big-city dweller, more accustomed to looking up at traffic helicopters and greedy pigeons than searching for waiting snakes in tree branches. Language ability, enthusiasm and curiosity don’t make up for a middle-aged body on top of clumsy feet. On various previous expeditions, seemingly following directly behind companions, I’d find a boot disappearing into a concealed hole, or a mudbank that had supported three people before me collapsing under my weight. On my last expedition with Ben, on an entirely different continent, a succession of injuries to my feet had left me no choice but to use duct tape to hold protective gauze in place when the damp terrain had defeated my stock of standard adhesive bandages.

In a patch of shallow water that looked just like several others that we had crossed, Alejandro stopped the canoe. He lightly secured it to protruding remnants of a thin submerged tree. No need for padlocks here – we hadn’t seen a human or a canoe.

We were told to wade toward the barely elevated landmass. I looked down into the water, fearing that it might be deeper than my rubber boots were high, and resolved to step as lightly as I could until we reached dry land. I pictured myself sinking in as I had once in New Guinea, when a camera worn around my waist had drowned. This time everything fragile went into a drysack.

The pool where Alejandro had encountered his adult anaconda was probably its home. The giant snakes can be found either in such pools or, less helpfully, lurking, silent under layers of fallen vegetation, waiting to detect the motion of approaching prey.

The pool was empty. The anaconda had moved house or was out for lunch.

We searched the island for signs of its presence. My skin itched and I dripped with sweat as I trailed our guides, but I managed to keep up, although of course our pace was slow and careful. Only our eyes moved quickly.

I told myself that Alejandro, heading our little troupe, would spot the anaconda before its appetite put us in any danger. Movies aside, I wasn’t sure that Amazonian anacondas would eat a human, their normal land-based prey being capybaras, jaguars, or monkeys, all a scale factor smaller even than Alejandro. Of course, other than the rustling high up in the canopy that Carlos had identified as monkeys – despite my experience I had failed to see anything beyond shadows and shaking branches – the only mammals we’d encountered that day were each other.

In snake terrain on dry land I walk heavy-footed, the resulting vibrations warning shy snakes in time for them to avoid me, but I have limited experience of snakes that may regard slow-moving humans as a possible happy meal. However, I had little choice: my clumsy rubber boots and post-pandemic heavy body weren’t made for balletic tiptoeing.

Stomping around in the squelch of rotting vegetation, damp leaves, and dangerously yielding humus, always looking for a safe place to put a heavy rubber boot, is hard work. It was harder still once Carlos had explained about anacondas lurking and looking for lunch, when any nearby section of deep vegetation screamed to be avoided. Alejandro, hoping to introduce us to the anaconda he’d promised, chose to check every single pool.

Having brought my cameras, I put one to use. I recorded tangles of lianas; jungle fungi, white or cream or tan; colourful cherry-sized fallen tree-fruit; and a highlight, the bright red exposed roots of a palm, like dozens of straws drinking from the earth. I don’t require jungle fauna to be happy – the flora is often fascinating enough. Alejandro said nothing. Carlos, on the other hand, warned me against touching, or worse, eating what I photographed.

Add rainforest humidity, the physical exertion and my ineffectual, constant flailing at insects: and the sum is sweat. I was drenched by the time I was back on the canoe. And I itched from insect bites, despite a morning round of repellent. From the acidic burning in my eyes, I suspected that sweat had washed the protective chemicals down from my forehead. Probably washed it away also from my neck, my arms, my back – everywhere where I now itched. I had been too sticky and too distracted with my camera to respray myself.

Ben, a snake lover who’d been dreaming of an encounter with an anaconda, was disappointed when we arrived at the canoe, perhaps ready to repeat the entire circuit, but Alejandro’s face told us that there was no point. Despite his name, it turned out he spoke little Spanish and Carlos translated, offering us a second expedition closer to sunset.

The anaconda had not been cooperative, a reminder that the wilderness is not a safari park with guaranteed outcomes. But as much as I too had been hopeful of seeing my first wild anaconda, and as much as I don’t enjoy hot humidity or being pestered by flying insects, that is what rainforests are about. I’d had an experience, seen some weird plants, and come away without an injury. I was happy.

As to Alejandro’s proposal, I’d enjoyed the island exploration, but the idea of repeating our search for the anaconda had limited appeal. Maybe a night walk near camp to find venomous frogs, another of Ben’s loves. Once I’d had a shower.

Alejandro didn't look like he'd shed a drop of sweat, but he did scratch himself a couple of times, not that I took that in until later.

Our return from the search probably retraced the route we'd taken that morning, but it was hard to tell. Once again, Alejandro navigated us through narrow channels emerging occasionally into quiet lagoons before entering the next concealed gap among the inundated trees. Whenever we left the shelter of the trees and entered wider patches of water, the midday sun baked and blinded us, but at least the humidity became more tolerable and fewer insects had the enthusiasm to follow. I watched for low-hanging branches and, other than a scratch or two, there were no injuries.

No ripples of an approaching anaconda in the water either, but besides Ben, I don’t think anyone spent much time looking.

When we arrived back at our base, my first priority was standing under the pipe attached to the giant rainwater barrel. I washed off the mix of sunblock, repellent and sweat, rinsed the long-sleeved shirt that added to the sweat but had promised protection against bugs and burns, and sprayed on a fresh layer of repellent.

After dinner, while I was savouring the last gritty mouthfuls of coffee, Alejandro sat down on the bench opposite. He took off his shirt. Carlos stood and peered at his back, probed with headtorch and fingers. Poured cachaça into a grimy glass and handed it to Alejandro. I could smell the strength of the sugarcane alcohol over my coffee.

'At least four,' Carlos said in Spanish. I translated for Ben, although it was probably unnecessary as he was standing next to me.

It took a few more minutes of linguistic gymnastics to puzzle out what Carlos had been counting.

Botfly larvae. Under Alejandro's skin. The lumps were visible.

I had read about them before coming. Botflies are bizarre, and frankly, disgusting. It’s often not the fly itself that is the problem – the female botfly apparently catches other insects, such as mosquitoes, and deposits its eggs on them. When the mosquito lands on a nice warm mammal, like us humans, our warmth causes the botfly eggs to hatch. The larvae emerge and move from the insect to their target, us. They enter our host bodies through a mosquito bite, through a pore, or through a graze, like the scratch of the branches I’d been trying to avoid on the canoe.

Botfly larvae breathe through an airhole they maintain in the skin as they grow, until they’re mature – when they crawl out of us, ready for the next step. In a video I watched with one eye closed, the larva was almost an inch long, not by any stretch an anaconda, but not something I want in my body. The holes the larvae leave generally heal quickly and something in the chemicals they secrete has an antibiotic effect, but when I’m in a damp rainforest, I’m nervous of any fresh holes in me.

As the larva grows, a lump on the skin like a callous, called a ‘warble’ (botflies are also called warble flies or gadflies), grows too and while some people claim to feel the larva moving under their skin, it is often the warble that calls attention to the spot. Alejandro’s were quite small, the larvae perhaps still young.

The larvae have tiny spines that act like fishhooks, making them tricky to remove until they are ready to leave. The best solution (assuming you aren't within convenient distance of a clinic) is to block their airholes with petroleum jelly to suffocate the larvae and then extract them. Some people cover the bites with duct tape – it takes a while but yanking off the tape often also yanks out the larva. However, as I know from personal experience, the tape can take more of you with it than you want.

Here in the rainforest the solution was different: nicotine.

Carlos lit a hand-rolled, unfiltered cigarette with our lighter and, once he had it going, sucked and blew, never inhaling, collecting smears of nicotine into the palm of his hand.

He painted the botfly sites with nicotine and waited.

In the meantime he gave Alejandro another glass of cachaça. Despite the alcohol, Alejandro remained silent while Carlos made his preparations. His eyes now looked slightly glazed.

We waited. I imagined the larva being increasingly oxygen-starved, pulling in their fishhook spines and burrowing their way out. Another glass of cachaça.

Insects. Insects kill more humans than any of the larger predators we fear. I thought of my great-uncle and his explorations. He’d have loved it here. In his career he’d published research, had frog and plant species named after him, and collected specimens still in museums. I had one picture of him – in one of his rainforests, in Asia I believe, with a large crocodile. He’d died young not killed by a crocodile or an anaconda, but from an insect bite, and he’d been buried far from home.

Carlos leaned close to Alejandro and directed his headtorch at the daubs of nicotine. He passed Alejandro another glass, full to the brim. It was time.

I have no idea how much pain Alejandro was in as Carlos pushed with his thumbnails to extract one larva after the other. They did not come easily. Alejandro said nothing until it was done.

He went to his sleeping mat early that night.

I looked at the dozens of bites on my own skin, at the raw grazes where branches had flayed me in passing, and wondered.