Only one more post for the week before I'm off for a few days, so here's a fun one (and part of the same clade of lizards as yesterday's).
Family Helodermatidae, Genus Heloderma – Beaded Lizards
Named for the protective osteoderms on their scales, these lizards are famous for their venom. These are large sturdy lizards, with thick tails used for fat storage. All are carnivores, eating small prey such as rodents, reptiles, birds, bugs and eggs. Ranging from the American Southwest into Central America, these are very popular in zoos. There are 5 species in total, all of which are kept in US zoos.
Gila Monster (Heloderma suspectum) – Abundant
A famous symbol of the American Southwest, this was the most common lizard in the survey. They are encountered largely in AZA zoos (both major league and small fry), reptile specialist zoos, and Southwest nature centers and desert museums. They are easy to distinguish from other members of the family by their yellow-and-black marbled pattern. They are the only beaded lizard native to the US, being found primarily in the deserts of Arizona (where they spend most of their time in underground burrows).
Though one Gila Monster has enough venom to kill an adult human, no fatality has occurred in nearly a century; however, the pain is considered to be excruciating. A drug that helps Type 2 diabetics to manage their insulin levels has been developed from their venom, so ironically they’ve likely saved more lives than they’ve ended. Despite being sluggish, sleepy animals – I’ve seen dozens in my lifetime, and I saw my first awake one a mere few months ago – they have been historically targeted due to their venomous bite, and so now are legally protected throughout their range.
There are two subspecies (supposedly), both present in US facilities – the southern Reticulated (H. s. suspectum) and the northern Banded (H. s. cinctum). They can be distinguished visually, but I have little information on what zoos hold which subspecies.
Taken at Zoo Knoxville by
@Coelacanth18
Mexican Beaded Lizard (H. horridum) – Very Common
Only about half as common or less in American zoos compared to Gila Monsters, but still one of the more common lizards generally. The color tends toward a black base with yellow spots. They’re also much larger than Gila Monsters, with an average length of 2-3 ft compared to the latter’s average of 1-2 ft. They inhabit both deserts and forests from northern Mexico down into Guatemala.
Taken at San Antonio Zoo by
@Ding Lingwei
Rio Fuerte Beaded Lizard (H. exasperatum) – Prevalent
Found within two river basins in western Mexico, this species was split from
H. horridum recently and looks extremely similar to its close relative. While only held by a handful of major zoos here, this species is more common than
H. horridum in Europe.
The following two species are much rarer in captivity, but are listed by the IUCN as Vulnerable and Endangered respectively.
Guatemalan Beaded Lizard (H. charlesbogerti) – Rare
Visually also similar to the Mexican Beaded Lizard. It is only found in the Motagua Valley of Guatemala, and in total numbers perhaps ~500 animals globally. Although it is rare in US collections, it is being actively bred; four were hatched in 2022 at the Oklahoma City Zoo (not on display there).
Taken at Zoo Atlanta by
@Ituri
Chiapan (Black) Beaded Lizard (H. alvarezi) – Rare
Also recently split from
horridum, this member of the genus is all black.
I didn't run a missing data check on the Guatemalan as I thought it would be more well-documented, but I've now found a couple references I missed. More opportunity to see this rare lizard than I thought!
