The reptilian body, with its scale-covered, thick, leathery skin and low energy
requirements, is in a sense preadapted to desert conditions. Unlike mammals,
too, it does not sweat and produces thick, pasty bodily wastes, which minimizes
water loss. A typical desert reptile, such as the desert night lizard (Xantusia
vigilis) of southwestern North America, exploits a variety of arid-land microclimates,
seeking out the underside of stones and crevices and resting beneath
the top surface of sand or excavating burrows. As its name suggests, the lizard
emerges at night to nose about in yucca and agave plants for insects and other
small creatures. As with other reptiles, the lizard is poikilothermic, enduring a
state of torpor during extreme cold that causes delayed muscle contractions and
even paralysis. This is when warm-blooded mammals and birds have the upper,
and faster, hand.
The second-largest lizard in the world, runner-up to the well-known Komodo
dragon, is the shy retiring perentie (Varanus giganteus) of Australia’s arid
center. Also known as the Queensland goanna, it reaches about 2.5 meters (8 ft.)
in length and is blotched and patched with creams, yellows, and browns, a
combination that blends perfectly into the rocky, arid scrub. It saunters about by
day inspecting burrows that may contain smaller lizards, snakes, or rabbits,
although it has been known to seize prey as large as juvenile kangaroos.
Another large and predatory Australian monitor lizard, up to 1.5 meters (5 ft.)
long, is the sand goanna (Varanus gouldii). It, too, dwells in the continent’s
“Red Center” and can swallow a whole rabbit. When disturbed, it flees at speed
on its four long legs, or even rears up on its two back legs—a tactic that gives it
the alternative name of racehorse goanna. If cornered, it puffs out its body,
hisses loudly, lashes its tail, and tries to bite the enemy.
Australia is home to dozens of other large lizards that are well-adapted to dry
conditions. The common blue-tongued skink (Tiliqua scincoides) ranges across
the eastern half of the continent, in arid scrub as well as woodland. It may grow
to 60 centimeters (23 in.) in length and eats an adaptable diet of plant matter,
including flowers and berries, and small animals such as snails and insects, as
well as carrion. Rather than turn and run on its smallish, weak legs if threatened,
the skink faces up to its aggressor, inflating its body, hissing loudly, and gaping
its jaws to reveal its startling large blue tongue. This martial attitude is no bluff,
and the skink may lunge, bite hard, and hold on while thrashing its body and tail.
The similar stumpy-tailed, or shingle-back, lizard (Trachydosaurus rugosus),
restricted to dry regions of southern Australia, also puts on a blue-tongued
defense display. It is difficult to distinguish the front and rear ends of this
reptile, as both are similarly shaped, perhaps as a means of distracting or
confusing predators. The stumpy tail holds a fat reserve for moisture and
nourishment for use when times are harsh.
Less than half the stumpy-tailed lizard’s size, at about 15 to 18 centimeters
(6–7 in.) long, the Australian desert skink (Egernia inornata) has a coppercolored
back and white bars along its flanks. It is diurnal, out by day to search
for insects and other prey. At night it retreats to its burrow under a clump of
spinifex or porcupine bush—one of many creatures that depend on this harsh,
spiky native grass for its home.
Perhaps the most impressive display of defense among Australian desert
lizards belongs to the bearded dragon (Aphibolurus barbatus), which reaches 60
to 70 centimeters (23–27 in.) in length. Dragons in desert areas are orangeyellow
or tawny, in contrast to those in woodlands farther east, which are brown
or gray. When aroused, the dragon puffs up, opens its mouth to reveal the
yellow-orange interior, and erects the spiky frill of skin over its chin. It also
unnervingly jumps toward the enemy. Several lizards living in soft sandy soil
show evolutionary trends to limb reduction or loss, wriggling the body from side
to side to “swim”
through their substrate, almost like a snake does. Only 10 centimeters (4 in.)
long, the Australian two-toed desert skink (Lerista bipes) of the continent’s dry
northwest is even less lizardlike, resembling rather a scaly worm. Its front legs
are absent, and its rear legs are thin and weedy, with just two toes each—one
large and one small. Instead of lower eyelids, it has transparent scales that
function as windows to see among soil particles as it “swims” through the sand
in its search for ants and termites.
The sandfish (Scincus philbyi) of the Middle East matches the red-yellow
color of the Arabian desert soil. It, too, wriggles like a fish but has retained large
legs and toes, the latter fringed with
thin scales, providing extended pedal surfaces that work as sandshoes. Its long,
chisel-shaped snout pushes through the soil as particles slip off its smooth,
pointed tail, which is also filled with fat as a food store. This little lizard, just 20
centimeters (8 in.) long, has strong jaws for crunching hard-cased prey such as
beetles and other insects. Active primarily at dawn and dusk, it sleeps by day
and may hibernate in colder months. Many other desert lizards live similar
burrowing lives, including the diminutive legless skinks of the Namib and
Kalahari, which are less than 10 centimeters (4 in.) long and resemble not so
much animals as pieces of broken-off brown shoelaces.
Only two of the world’s lizards have venomous bites, and both of these are
inhabitants of the arid lands of southwest and southern North America. The gila
monster (Heloderma suspectum) grows to about 55 centimeters (21.5 in.) and
warns off predators with its gaudy pink, yellow, or orange blotchy stripes. As in
its 80-centimeter-long (31 in.), black-and-yellow venomous cousin, the Mexican
beaded lizard (Heloderma horridum), the lizard’s scales are domed or rounded,
resembling small, shiny beads, and are adjacent rather than over-lapping. The
venom is made in glands in the lower jaw, and as the lizard bites and chews, it
flows into the victim via the grooved front teeth. A well-fed gila monster has a
torpedo-shaped tail full of fatty food stores that can last for months. Named after
the Gila Basin in Arizona, this predator is mainly nocturnal and feeds on small
creatures, such as insects, mice, birds, and other lizards, as well as on bird and
lizard eggs. The bites of these reptiles are rarely fatal to humans but can be
extremely painful.
For humans and prey alike some of the most feared desert creatures are
poisonous snakes. The looping motion of the sidewinder (Crotalus cerastes)
from North America’s southwest has already been described (see p. 91). This
agile snake grows to about 75 centimeters (29 in.) in length and hunts small
mammals and lizards by night, holing up for the day in a crevice, under a bush,
or in an old rodent burrow. It has a distinctive “horn” over each eye and black
stripes along the top and sides of the neck that widen and break into diamondshaped
black patches along the top of the body.
The Namib Desert has its own exponent of this locomotive method, the desert
sidewinding viper (Bitis peringueyi; see illus., p. 91). Only about 25 centimeters
(10 in.) in length, and with a dark brown upper body that shades to lighter brown
below, it glides over the dunes with typical sidewinding skill and is just as
deadly to its prey. Another sidewinding snake is the exceptionally dangerous
saw-scaled viper, or saw-scaled adder (Echis carinatus), found in the Sahara and
in deserts of the Middle and Near East. This is one of the world’s most
venomous creatures, and its bites kill several people each year, especially in and
around the Sahara. To warn off potential predators, it coils up to rub the serrated
scales on the sides of its body against each other, producing a rasping sound. In
addition to the usual snake diet of small mammals, birds, and lizards, the sawscaled
viper tackles creatures that are themselves venomous, including large
centipedes and scorpions.
Every desert region has a scattering of poisonous snakes, such as the snouted
lancehead of the Atacama and the manushi, or Asiatic pit viper (Agkistrodon
halys), of the Gobi. The manushi reaches 75 centimeters (29 in.) in length and
ranges north from the Asian desert, across the steppes toward the great conifer
forests of the northern taiga. It has rings of dark gray, brown, or black
alternating with light yellow, cream, or fawn, and eats mainly small mammals. It
hibernates from about October to March, due to the cold in the north of its range
and the aridity in the south.
Some snake surveys point to Australia as home to eight of the world’s ten
most poisonous land snakes. One of these, the fierce snake (Parademansia
microlepidota), is very large—at 2.5 meters (72 in.) in length—very fast, and
very venomous, and inhabits the arid zones in the center-east of the continent.
The eastern brown snake (Pseudonaja textilis) is another sizeable species, at 1.5
meters long (60 in.), and ranges into the continent’s eastern deserts. It is an
efficient predator of small animals. When it strikes, it does not jab in its poison
and then retreat, but hangs on with its fangs so as to inject additional venom.
Less dangerous to humans is the bandy-bandy (Vermicella annulata), a snake of
about 80 centimeters (30 in.) long with alternating black-and-white hoops along
its body. It hunts smaller snakes and lizards and, for a top carnivore, is relatively
common throughout the Central Australian desert regions.
All of these snakes benefit from their carnivorous diet, which usually contains
plenty of moisture in the form of blood and other body fluids. Like other
reptiles, they use the heat retained by the desert soil to incubate their eggs,
which in nearly all cases are buried by the mother and then abandoned.