Helmeted Iguana

Fascinating facts about the Helmeted Iguana

• The lizard is named for the thing on its head. A tall casque rises from the back of the skull and runs down the neck, looking for all the world like a helmet, and it does not stop there: it tapers into a saw-toothed ridge that carries on down the animal's back. Both males and females have it, and it is larger in males. For all that architecture, the animal underneath is small. A mature one measures about 9 to 12 centimetres from snout to vent, on long slim legs and very long toes.
• It is an extreme sit-and-wait predator, and the emphasis belongs on extreme. Its foraging is brief and infrequent; most of its day is spent not hunting at all, but waiting for something to walk past. Insects, spiders, worms and other lizards all count, and when they are available it specialises in unusually large arthropods and cicadas. If the waiting produces nothing it will give in and go looking, and when it does it picks the slow and easy prey, which is roughly what you would expect of an animal whose whole design is built around not moving.
• Stillness is also its defence. It is very wary, and it freezes at the approach of danger from as much as 15 metres away, long before most animals would react at all. It can change the colour of its skin from dark to light and back again, which serves as camouflage against bark and leaf litter. Grey, olive, brown, black or reddish brown, blotched irregularly, a motionless helmeted iguana on a trunk is close to invisible.
• It holds still so long that other living things start treating it as ground. Its skin has been recorded as a growing surface for Physarum pusillum, a slime mould, which is a strange enough fate for a lizard. It goes further: this is the only vertebrate ever observed with a cormophytic plant, a true stemmed and leafed plant, growing on it. Most animals are habitat for parasites. This one has been habitat for a garden.
• The nest is a hole in the forest floor. A female lays five or six eggs in a depression she makes in the ground, which is a modest clutch, and there is a suggestion that the crest on her head is what she digs it with. The species is mostly a creature of trees, living in primary and secondary rainforest from Chiapas in southern Mexico down to north-western Colombia, but it comes down to hunt among the leaf litter, and it comes down to lay.

At a glance

About the Helmeted Iguana

The helmeted iguana is a medium-sized New World lizard of the family Corytophanidae, the same family as the basilisks, and it is known by a long list of names: smooth helmeted iguana, helmeted basilisk, elegant helmeted lizard. It lives from Chiapas in southern Mexico through Central America to north-western Colombia, in primary and secondary mesic rainforest, spending most of its life in the trees but hunting on the forest floor as well, where leaf litter serves as a micro-habitat. It is grey, olive, brown, black or reddish brown with irregular blotches, and it can shift that colour lighter or darker. The casque on its head, tapering to a saw-toothed ridge down the back, is what gives it every one of its names. It is a non-heliotherm, which sets it apart from most lizards: it does not use the sun to raise its body temperature, holding instead at around 26 degrees Celsius, close to the temperature of the forest floor where it lives. Almost everything about it is built around waiting, and waiting is also what makes it so easy to walk past.

Helmeted Iguana photographed on Feravox

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