Tim Cockerill returns to take a look at some leeches in a short piece produced for YouTube's Geek Week back in August. If you're a bit squeamish this probably isn't for you! [youtube=http://www.youtube.com/watch?v=jerqq06uxAo&w=640&h=360]
We couldn't really make a video about leeches without showing off their impressive feeding apparatus, a Y-shaped jaw packing in roughly 300 teeth! This was a tricky shot to achieve, we had to persuade the leech to attach to a glass plate, holding it in position by hand, allowing us to shoot from below with a macro lens. It was a great sight to behold once we finally got it and it certainly helps bring something to the film that you hopefully wont have seen elsewhere.
We also had to get some footage of a leech feeding, so we set one loose on Tim's arm, shooting a time-lapse to demonstrate how much they can expand during the feeding. Once it had attached to feed, we were very much at the mercy of the Leech's hunger as we couldn't shoot the final shots until it had detached. As Tim mentions in the film, it's not a good idea to pull or burn leeches off as this may cause them to vomit their stomach contents back into the open wound - not a good idea if you don't know what the leech as been feeding on previously. The best course of action to take is to let detach when it's good and ready.
We also wanted to dispel a common myth about leeches using anaesthetics to dull the pain the sensation of pain whilst feeding - as Tim reports there's little scientific evidence to support this and he certainly reports to feel a stinging sensation as the leech feeds on him.
After about 3 hours the leech was finally full and very happily detached from Tim's arm - during 'the feeding' the leech utilises an anti-coagulant (called hirudin) and as you can see in the film this prevents the blood from clotting, causing the wound to bleed profusely four a couple of hours after it's detached!