Zookeepers measure the length of a pueblan milk snake in the Reptile House of ZSL London Zoo as part of their annual weighing and measuring of their animals on August 25, 2011 in London, England. The heights and weights of over 750 different animal species at the zoo are recorded into the International Species Information System, to monitor their health and share the data with other zoos across the world. (Photo by Oli Scarff/Getty Images)

Zookeeper Sebastian Grant (R) weighs Dirk, a giant Galapagos tortoise, at ZSL London Zoo as part of their annual weighing and measuring of their animals on August 25, 2011 in London, England. (Photo by Oli Scarff/Getty Images)

Dirk (L), a giant Galapagos tortoise, attempts to mate in his enclosure at ZSL London Zoo after being weighed as part of the zoo's annual weighing and measuring of their animals on August 25, 2011 in London, England. (Photo by Oli Scarff/Getty Images)

A chameleon waits to be weighed and measured in the reptile house at ZSL London Zoo as part of their annual weighing and measuring of their animals on August 25, 2011 in London, England. (Photo by Oli Scarff/Getty Images)

Zookeeper Jeff Lambert measures Jacqueline, a Mexican Red-Kneed Tarantula, at ZSL London Zoo as part of their annual weighing and measuring of their animals on August 25, 2011 in London, England. (Photo by Oli Scarff/Getty Images)

Tammy, a Southern Tamandua, is weighed at ZSL London Zoo as part of their annual weighing and measuring of their animals on August 25, 2011 in London, England. (Photo by Oli Scarff/Getty Images)