Click here: The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts, Part I, to read the first part of this article.
Monitor lizards exhibit an extraordinary degree of intelligence and retain what they have learned for long periods. Gould’s monitors (V. gouldii) have been observed taking indirect routes when chasing rabbits. Rather than running directly after the rabbit, they veer off in a direction that takes them away from the animal, but leaves the lizard in a position to intercept the rabbit at the mouth of its burrow!
Parentie monitors (V. giganteus) seeking animals hidden within burrows do not dig away at the burrow entrance (as would a foolish dog!) but rather sniff the ground several feet away. Once they locate the underground position of their prey, they dig directly down to reach it, keeping an eye on the entrance as well.
An Experience with a Bright Monitor
I have often had the good fortune to observe monitor intelligence in action. While working at the Bronx Zoo, I once looked up from a phone conversation to see a 6 foot long crocodile monitor (V. salvadorii) go shooting by, followed by an equally fast-moving coworker of mine. We cornered the animal behind a large cage, where he remained as long as we were in view. As soon as we moved off to either side, he cautiously peered around the cage and looked both right and left, to fix our new positions. The lizard most definitely did not want either of us sneaking up on him, and made sure he saw both of us at all times.
The stout fellow was recaptured – with more wear and tear to us than he! Monitors are incredibly strong – a 7 foot long water monitor (V. salvator) I worked with was able to move along with myself and 2 other strong men trying to pin him down – this despite being rather seriously ill.
In 2005, Dr. Bryan Frye and researchers at Australia’s Melbourne University discovered that several species of monitor lizards, including the Komodo dragon, V. komodoensis and the lace monitor V. varius, produce venoms of varying strengths. Lace monitor venom was subsequently shown to cause the lizard’s prey to rapidly loss consciousness by affecting the blood’s pressure and clotting ability.
Until this discovery, bacteria in the mouth of the Komodo dragon were thought to be responsible for the quick onset of death seen in deer, goats and other large animals bitten by these lizards. While such bacteria no doubt add to the trauma associated with a bite, it now seems certain that venom delivers the knockout blow. A combination of venom and bacterial infection is also the likely source of the strong reaction often associated with bites inflicted by monitor lizards upon people.
The Bearded Dragon, Pagona vitticeps, a popular pet species not related to the monitor lizards, was also shown to produce mild venom – other members of the lizard family Agamidae are being studied.
An interesting article on Florida’s introduced Nile monitor lizards is posted at: