What have pigs' sperm, leeches and 31 pairs of knickers got in common?
Something strange is lurking inside the pillar box at the end of your road. Check your mail very carefully, because what is among the final demands, circulars and love letters might make you want to reach for the rubber gloves. Some very bizarre items are now being sent through the post.

"We ship hungry leeches by mail," says Carl Peters, a zoologist from Biopharm UK. "We starve them for six months because our customers, hospitals, like them to bite on contact." Leeches are used after plastic and reconstructive surgery to clear the smaller blockages. "How they are packaged depends on the weather, in summertime they travel with their own icepack to stay cool." Biopharm UK sends out up to 40,000 leeches a year; in the right conditions they can survive for weeks in their parcels.

"Old Victorian Royal Mail buildings are perfect for storing pigs' semen," explains Walter Swann, General Manager of JSR Healthbred SDS which provides boars' sperm for artificial insemination. "Our local one, in York, is actually under ground which is brilliant, because in summer temperatures stay fairly constant. The ideal temperature for semen preservation is 17 to 20 degrees - the average temperature of a post office sorting depot."

Walter Swann finds the post is quick and reliable. "We have farmers all over Britain, from north of Inverness to Cornwall, while our centre is in Yorkshire and the semen has to be there the next day. If it doesn't arrive while the sow is on heat there is no point. We are the envy of Europe and worldwide because they cannot believe that anywhere in Britain can get semen the next day." It's great to find a new source of national pride. We might have lost Hong Kong but at least we can send boars' sperm through the post.

What make a sane person order bugs to be posted to them? The answer is an attack of vine weevils. This two-inch long brownish insect has become a major pest with devastating effects on plants in containers. "People are turning away from toxic chemicals because they don't really work," says Annie Manners of the biological control advice service Green Gardener. "The pests build up resistance, breeding a superbug. Gardeners ring me up almost in tears because the evil weevil has chomped its way through their conservatory. A nematode is very effective in combating the weevil. You can fit 10 million of them into an eight centimetre long tube which we post to you."

All these items are knowingly carried by the Royal Mail, the firms having discussed packaging and safety with their local Customer Service Centre. However, there is little chance of controlling the general public, whose brown paper parcels contain some unlikely secrets.

"I'm now ready to confess," says Helen O'Brian, a 30-year-old dental hygienist. "When I was only eighteen, I had a boyfriend who was a really nasty piece of work. He was very abusive and so I felt vindicated in using the post to get my revenge. He was hysterical about spiders, running and screaming if he saw just one. I managed to pack about half-a-dozen spiders into a matchbox and posted it to him."

Helen never discovered if her retribution was successful. "I fantasised about him opening the package and going crazy and me laughing like a witch. However, I did have an irrational fear that he would send me a dead rat, so I opened all my parcels very gingerly."

Most chain letters are a form of harassment, threatening bad luck if recipients break the chain, but others promise very strange rewards. Kate Richardson, a 35-year-old therapist, admits to participating in a knickers chain: "Although I don't generally approve this one intrigued me because I could end up getting 31 pairs of knickers, which is always handy, and all I had to do was put down my size."

Kate sent parcels to the two names at the top of the list: "I knew a couple of the names, they seemed to be all sensible middle-class women who should be out walking dogs rather than falling foul of a knickers chain letter. It was exciting opening the parcels I received, although my husband thought I was completely mad. I ended up with four pairs - they were all clean, which was a relief."

Sometimes there is a fine line between laughter and tears. The final wish for many people is that their ashes should be scattered in a favourite beauty spot, but if they die abroad the post is the simplest way to repatriate them. "I felt that I was in a Joe Orton comedy," says Sam Griffin, a 37- year-old market researcher whose partner was German and opted to have his final care in his home country. "His family did not feel comfortable about flying over with the urn. I told them to send it me and didn't give a second thought about how it would arrive. When a Post Office van pulled up, I got excited about a mystery parcel until I read the label and realised I was holding my partner in my arms again. It was a very surreal moment"n