Komodo dragons, sometimes called Komodo monitors, are the largest living species of lizard and can grow to lengths of 3 metres, weighing up to 70kg. Their large size means that they dominate the island ecosystems of Indonesia where there are no other carnivorous animals for them to compete with and they prey upon invertebrates, birds and mammals alike. Komodo dragons are highly intelligent have frequently been seen hunting in packs - the only species of lizard known to do this!
The large size of the lizards is unusual and is believed to be due a phenomenon called island gigantism, which is where species that are isolated on islands can grow to much larger sizes than those on mainlands due to the lack of competition for resources and the absence of predators. Island gigantism explains the Komodo dragons huge size in part, but the species also belongs to the ancient Asian Varanus genus that contained many species of large lizard, so it likely that the dragons' should be big anyway. The genus was isolated in Australia 40 million years ago and many larger cousins of the Komodo dragon once stalked its lands. However these larger cousins, which were species of megafauna, became extinct with the arrival of humans in Australia and the changes that we caused to their environment. Thus only their smaller cousins, which are believed to have evolved in Queensland and spread into Indonesia during a period of glaciation when sea levels were lower, survive today.
The one the most well known facts about Komodo dragons is that they have saliva that contains an extremely high number of bacterial species, which frequently causes fatal infections in animals that they bite. However, this is a misconception and although Komodo dragons do have a large range of bacterial species in their saliva, which can be as high as 57 different species, it is not unusually high for a predator. In fact, human saliva contains many more species of bacteria than a Komodo dragon and we have one of the most infectious bites of any organism in the world! However, although Komodo saliva contains no more types of bacteria than other predators, it is still highly unusual. This is because when Komodos bite their prey, they tear off its flesh by pulling their head back in a circular motion, which works in the same way as a can opener. This twisting motion is very damaging to their teeth and as a result, their gums are prone to bleeding. Thus, their saliva often has a high blood content, which enables bacterial colonies to grow to extremely large sizes so that when they bite their prey, they overload its blood with bacteria - giving the wound a greater chance of becoming infected!
In addition to having incredibly infectious saliva, Komodo dragons are also poisonous. This was only recently discovered and makes Komodo dragons one of only three known poisonous species of lizard. (The other two are the American Gila monster and the Mexican beaded lizard). Its venom, secreted into its saliva from two large glands beneath its tongue, is highly toxic and works like an anti-coagulant to stop blood from clotting. Clotting is the body's normal response to a cut and basically, once the body realises it's been cut it activates certain proteins in plasma, the fluid that erythrocytes (red blood cells) are suspended in. The activated proteins, called platelets, change shape and form a 'net' that traps erythrocytes at the site of the wound, forming a scab. As I'm sure you know, scabs prevent blood loss, so anti-coagulant poisons stop this from happening. As a result of this, an animal bitten by a Komodo dragon will eventually bleed to death, whilst becoming weaker and weaker as they lose more blood. Komodos take advantage of this by biting their prey a few times and then backing off, which reduces their risk of injury from their prey. They then follow the wounded animal at a safe distance until it dies, or becomes too weak to struggle.
This allows them to bring down animals much larger than themselves and sadly, the lizards have been known to kill humans. However, despite being fearsome predators with deadly saliva and the intelligence and brute force needed for ambushes, Komodo dragons are predominately scavengers that feed off carrion, eating anything that they come across.
Unfortunately, the loss of Komodo dragons habitat due to human activity, illegal poaching and the effects of improperly managed tourism means that there are now less than 5, 000 individuals living in the wild and it is believed that there may be as few as 350 breeding females left. Consequently, the species is classified as 'vulnerable' by the IUCN and may soon disappear, being on the agency's Red List.