It was a warm Tuesday morning, the beginning of my second week in Bloomsbury, London, and I was smoking a cigarette on the stone steps of the apartment building two doors down from mine. A man wearing overalls got out of a small van, took a silver canister from the passenger seat and strapped it across his shoulder. He wore the canister and the attached hose in a holster, and as he walked across the road towards me the canister bounced on his stomach. The canister looked as if it might belong to a fumigation outfit, and so, when he reached the bottom step of the building, I asked: “What’s in the canister?”

He stopped walking and smiled. “A wonderful spray.”

“What’s it for?”

He smiled again. “Bed bugs.” He moved the holster strap across his shoulder, and then, with the canister resting on his hip, he put his back against the stairwell rail and relaxed, with one hand in his pocket. “It’s for a man on the fifth floor who thinks he has bed bugs.”

I lit another cigarette. “Really? Has he been bitten?”

“They might not be bed bugs. He sounds like he might be an alcoholic or a drug addict. Or he might be allergic to something he ate.”

“What makes you think he’s a drug addict?”

“He might not be a drug addict. He might be one of those people with really sensitive skin.”

“What do you mean?”

“It’s rare, but it does happen. Even the slightest breeze on their face or hand can make them feel pain.” He ran the back of his knuckles lightly across his face in impersonation of a breeze. He did it the way somebody in a pantomime might do it. He said “ouch” at the end. “But I’ve only ever had one of these cases and he thought he was being bitten, but he wasn’t.”

“Sounds bad,” I said.

“Sometimes people who can’t sleep for a long time think they are being bitten during the night when they aren’t.”

“Really?”

He reached into his pocket and took out a pair of latex gloves. I watched the plastic stretch across his short, black fingers. The gloves were milky white, opaque, and the left-hand glove had a hole in the palm.

“They don’t last,” he said.

He pulled the torn glove off and took a fresh one from his pocket. But it was the right-hand glove, not the left, and he put it away again.

“I better get up there. Can’t stand here all day.”

“Thanks for telling me about the spray.”

“Welcome.”

He buzzed the video-entry phone and a man answered. There’s not much I could tell about the man upstairs from his voice, but this is what I imagined: a young man who lives alone opens his front door and leaves it open. Then he sits in a kitchen chair in the middle of an otherwise empty living room, and waits. When the exterminator reaches the fifth floor, the man doesn’t go to the door to greet him. He doesn’t even stand. He sits in the chair in the middle of the room. When the fumigator comes in, the man looks towards the bedroom door and says: “I haven’t had a proper sleep in a week and I think you’ll need more than one bottle of that stuff to get rid of them.”

Two days later I realised why I imagined a man sitting in the middle of an otherwise bare room. In 1996 a man I was living with told me about the time he lived alone in a bed-sit in Amsterdam. It was damp, dark and cold. One day while he was working at his desk, he began to scratch his arms. The next day he was scratching his legs. By the third day he was scratching violently and constantly, especially his forearms. His legs were itchy and irritated, from the middle of the thigh down. It was becoming difficult to work but he had no choice. He had a deadline: his book was due at the publishers in four days.

He was being bitten by something in the bed-sit but he didn’t know what it was. He couldn’t see any insects, nor could he hear them. He asked his neighbours but nobody in the building had any explanation. The block of flats, they told him, had never had bugs of any kind. One neighbour even came inside and looked around.

“I’ve never heard of this before. I can’t help you. I don’t know what it is.”

Then, during the night of the fifth day, my friend caught a flea while it was biting his naked forearm. The bed-sit was infested and he was being bitten – below the hemline of his short pyjama bottoms and sleeves – by fleas. There were hundreds of fleas. Probably thousands.

The next day – the sixth day – my friend went back to one of his neighbours and asked if the previous tenant had owned a dog or a cat. Yes, they had. They had a big black dog. His deadline was less than 48 hours away and he needed to rid the bed-sit of fleas. He couldn’t afford an exterminator; fumigation wasn’t an option. But he couldn’t live with this. He was furious with the fleas, driven mad by their biting. He shouted and cursed at them. He was alone, but not alone; miserable and sore.

And then, after six days of infestation, a day before his deadline, he went to the local pet shop. When he got home he put a kitchen chair in the middle of the bare room and surrounded the chair with saucepans of water. Then he put two flea collars on each of his ankles and three flea collars on each of his wrists. And just to be sure, he put several more flea collars around the legs of the chair and around the slats in the back of the chair. Then he sat in the chair in the middle of the room and waited for the fleas to come in the night and try to bite him.

I asked my friend whether his plan had worked. I think he said, “Not at all,” but when I play the story in my mind, it always ends with saucepans of water filled with drowned fleas and a writer standing on a kitchen chair shouting: “I did it!”