Basel Zoo is now home to Gila monsters, a species of heloderma or beaded lizard. Terrarium 52 has been turned into a desert terrarium, recreating a habitat reminiscent of the desert landscape of the south-west United States. Three young Gila monsters from a private reptile breeder have moved into this terrarium.

Two species of the heloderma family are the most venomous species of lizard in the world. For a long time, they were considered to be the only venomous species of lizard, that is until an enzyme that can stop the blood from clotting was discovered in Komodo dragons.

Venomous, but not lethal

Unlike in venomous snakes, the some four-centimetre venom glands in heloderma lizards are found in the lower jaw. Their venom makes its way from the glands along a channel between their lips and jaw bone to their teeth, which are around six centimetres long, pointed and slightly curved towards the back of their mouths. The venom is released into the bite wounds on their prey via the grooves in their teeth. Also unlike venomous snakes, heloderma lizards do not immediately let go of their prey after they have bitten them. Instead, they latch on and work the venom into their prey. The venom affects the nervous system and is highly toxic. However, heloderma lizards only produce this venom in small amounts, meaning their bite will not prove fatal for a healthy human adult. Nonetheless, the effects of this venom are still deeply unpleasant and include severe swelling, nausea, vomiting, an elevated temperature and raised blood pressure. There is no antidote.

The life of a Gila monster

Measuring in at a total of 50-60 centimetres, Gila monsters (Heloderma suspectum) are significantly smaller than Mexican beaded lizards (Heloderma horridum), which were previously kept at Basel Zoo and grew up to a length of 90 centimetres. With their large torso, broad head and short legs, Gila monsters give the impression of being rather on the plump side, but they can turn around in the blink of an eye. Their body is covered in hemispherical studs and they have very small eyes, which – along with their short extremities – are a sign that they spend a lot of their time underground and building burrows. These lizards live in the south-west United States and northern Mexico, from the Mojave Desert to the Sonoran Desert. Even though they can be found in deserts, they are more common in dry bush savanna and sparse woodland. The lizards most likely got their name from the Gila river, which runs through Arizona and south-west New Mexico.

Gila monsters spend the dry season in their self-excavated burrows, drawing on the fat reserves stored in their tails. They mostly feed on very young small mammals, and on the eggs of other reptiles and ground-nesting birds. Gila monsters also reproduce by laying eggs. In the spring, the males often engage in fighting rituals, and the lizards then go on to mate with the females shortly afterwards. Five to eight weeks later, often with the onset the summer rains, the females will lay between two and a dozen eggs. These will take four to five months to hatch.