Beaded Lizards are native only to Mexico and Guatemala. The 4
subspecies of the wonderfully-named Heloderma horridum
(horrible studded-skin) were given full species status
in 2013 (not accepted by all). They are the nominal Mexican
Beaded from northern Mexico, H. horridum,
the Rio Fuerte Beaded from central Mexico, H. exasperatum
(most photos on this page are this), and the Chiapan Beaded
from southern Mexico, H. alvarezi. All these have contiguous
ranges and live in forest habitat. The extremely rare
and critically endangered Guatemalan Beaded Lizard, H.
charlesborgeti, is separated from these in one dry
valley in Guatemala.
3 species of Beaded Lizard look similar with an armour
of bony beads protecting their skin and a black base with
off-white or yellow spots/markings and a banded tail telling
predators they are toxic.
The Beaded Lizard is one of the two confirmed venomous
lizards in the world, the other being its close relative the
Gila Monster. The Chiapan is usually plain black, grey or
brown. They can grow to some 3 feet (1 metre) long, (larger
than the Gila Monster).
Since their diet is almost entirely eggs of reptiles and
birds, the venom is probably for defence (used by humans in
Beaded Lizards have forked tongues to taste their environment
like Monitor Lizards and snakes. Unlike most lizards, their
tails do not break off and regenerate, since the tails are
used to store fat for the winter. The semi arboreal lizard
spends most of the day and night in underground burrows.