The rainforests of northern Queensland are breathtaking - a teeming, screeching world of variety. But what's it like sharing this with people you've never met? Kate Spicer finds out on an expedition

Little green ants have the same amount of vitamin C as 20 oranges, Jamie assures us. I lick their spiky little citric bums for maximum nutritional benefit. This is Daintree National Park, in far north Queensland, the oldest rainforest in the world. But we are touring in the relative comfort of a 4x4, while being gently versed in the law of the jungle.

Our guide is young and likeable, his wit as dry as his accent is strong. Jamie play-acts the dumb Aussie fella to the joy of his passengers; we are seduced by his elastic vowels and self-deprecating stories.

I started my trip to the top right-hand corner of Australia alone, but I have joined a group expedition to leave the ocean behind. We are all women, bar one German and one Frenchman. Our route takes us south out of Cairns past fruit stalls and sugar-cane fields where hundreds of birds of prey flock together like starlings over the fast food in the freshly ploughed fields. Just a few miles inland, in sugar towns like Babinda and Innisfail you hit a conservative Australia that seems stuck in the Fifties: a travelling Christian circus - the "Tent of Promise". In these old tin- and gold-mining towns, there are red letterboxes and sparse post offices that sell toasted sandwiches and coffee.

The architecture is clapperboard houses built on stilts to protect against the termites, and allow cool air to circulate beneath them. There are also tin agricultural buildings that have been internationally eulogised in the modern movement work of Pritzker Prize-winning Australian architect, Glenn Murcutt. Heading west, we skirt around the Atherton Tableland back into the dense green forest. We stop at waterfalls and rock slides hidden away up paths into the rainforest.

In the gloaming of a rainy evening we swim in a warm volcanic lake with water an almost phosphorescent shade of dark blue. We have been on the road only six hours. Yet the two members of the group who are travelling together are already a little snippy. Emily the vet is exuberantly diving into any water, croc-infested aside, we come across, while Clare the law student finds it all a bit scary. "Bye then Emily," Clare says, with sarcastic sharpness.

Earlier, sitting in the 4x4, Tania, a 37-year-old teacher from Cardiff had given me some basic advice about joining escorted trips: "When you are in a group you need to know yourself, you need to know when to integrate with the group and when you need time out by yourself. This is not about friends 24/7."

After a swim I find a couple of leeches attached to my ankles. I watch them getting fat until we stop to buy fruit and Jamie burns them off with a lit cigarette. Earlier Emily had sat patiently while a tick that had burrowed into her back was removed with vinegar, whereas I scream and squirm, and humiliate myself.

We make several walks on well-maintained boardwalks above the forest floor. Jamie points out tree snakes and fist-sized spiders. The rainforest's infinite variety is boggling. The parasitic fig tree grows up around a host trunk and slowly strangles it, and throws down a lace of roots from branches 30 feet up. The larger ones are more like cathedrals than trees. Looping vines, curled like telephone cords, dangle from the dense green canopy.

From giant leaves to teeny mosses in every green imaginable, the jungle has a million layers of life on life on life. Boulder-sized basket ferns grow in the crook of trunk and branch. The air smells green, and vibrates with vigour and oxygen. It teems with life, heard but unseen. Some of the spiders bark like dogs. There are cycads here, fern-like trees that date back 280 million years.

We stay in bunk rooms and cheap hotels. The one thing you don't want from a hotel is that it feels like home. My room at the Paramon Pub did not disappoint. The building resembles a saloon from a spaghetti Western. Our group took every room in the place. I snuck in fast enough to bag the honeymoon suite. A dilapidated wardrobe in the corner had a huge hole kicked into it, but over the bed hung a canopy of nylon lace. Drinking icy schooners of beer with a toothless local mechanic later, I was told that a man murdered his wife and then shot himself in that room. But not even ghosts could stave off sleep that night.

Another night we sleep in a smart hostel, deep in the peaceful heart of the rainforest. Not that the rainforest is ever still; as I go to bed a brown and white wild pig forages in the palms on the side of the camp. I fall asleep in our bunk room listening to the rain thrash the leaves.

The others had stayed up to drink cheap beer and watch the rugby in the bar. I'm not sure I've got the hang of the group mentality, quite yet.

Towards the end of each day we always go to find water, sea, lake or river pools. At Cape Tribulation the dropping sun shines across the wet sand and silvers it. Bleached dead branches of mangrove, in parts charred black and grey, are half-buried skeletons in the sand. Scaly rocks peek through the rippling waves like crocs submerging. This is not a cosy paradise. I break a mangrove leaf and curious, lick it to taste the salty water inside.

"God, that could be poisonous - be careful." An American group member has been watching me. Irritation rises, but I turn smiling and we walk together back to the group. Away, behind the beach, the rainforest ascends. Australia is familiar, organised, and welcoming, but you never escape that sensation of being a long, long way from home. As DH Lawrence wrote, "It seems so old, as if it had missed all this Semite-Egyptian-Indo-European vast era of history, and was coal age, the age of great ferns and mosses." We take a break from it all and play football, happily, together.

Fly to Cairns via Singapore on British Airways/Qantas/ Australian Airlines, or via Hong Kong on Cathay Pacific. Kate Spicer paid about £100 for a "Rainforest Adventure" with Jungle Tours (00 61 7 4032 5600,