They are running courses which aim to explain the true nature of things creepy-crawly, as well as allow people to confront their fears - in the flesh.

By the end of the day, people who would normally run a mile can sit in the same room as some of the most ferocious looking spiders.

The innovative course at Bristol is being run by Mary Ison, an expert on phobias.

She said: "A phobia is an irrational fear. It can make people the subject of ridicule."

The course has a teaching session on spiders, followed by relaxation or even hypnotherapy - before the students can get close to the spiders.

The courses have been so successful that the zoo is planning new days focusing on fear of snakes and other animals.

Happy customer

Susan Kerr has managed to conquer at least some of her fears following the day.

She said: "I couldn't even look at a picture of a spider without feeling sick and very upset.

"It's totally irrational. Your mind is telling you one thing and your body another."

Now, however, she can even cope with extracting spiders who have dropped into the bath at home.

"It's given me a huge amount of confidence."

The exact origin of phobias is unknown, but it is thought that the irrational fears could be representative of deeper fears.

Other theories include the development of a conditioned response to a trauma early in life - for example being scared by a spider when young.

Some psychologists even believe that the response to some animals could be a re-emergence of primeval feelings from a time when spiders were widely feared.

However, it is possible to develop a phobia about just about anything, with some of the more unusual being apeirophobia, the fear of infinity, chronomentrophobia, the fear of clocks and gephyrophobia - a fear of crossing bridges.