As part of YouTube Geek Week, the Ri and Dr Tim Cockerill explore the science of Leeches. As an entomologist, Tim is used to getting up close and personal with insects and here he lets a hungry leech feed on his arm - all in the name of science. By observing the feeding process (for over three hours!), Tim explores the science behind how leeches live, thrive and survive and challenges some popular misconceptions along the way. Warning: contains footage of blood. Find out more about Leeches at http://en.wikipedia.org/wiki/Leeches Watch more YouTube Geek Week videos at http://youtube.com/geekweek Subscribe to this Channel! http://bit.ly/RiSubscRibe The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter