As in virtually every terrestrial habitat insects are the most common creatures in
a typical desert. The planet’s most brilliant survivors, they are able to adapt to
the harshest of conditions. Their small size means they can access a wide variety
of microclimates—such as those provided by cool and moist nooks and
crannies—many of which reptiles, birds, and mammals are unable to exploit.
The insect “skin,” or cuticle, is waxy and waterproof and resists moisture
passage and desiccation so effectively that some species, especially beetles, are
able to travel many meters in the midday desert sun without sustaining damage.
Insects also perform a vital role as interstitial links in the amy food chains that
connect plants to small carnivores.
Ants like termites are especially widerspread in deserts. Despite belonging to
two different insect orders respectively the llymenoptera and lsoptera both ants
and termites have superficial resemblances in terms of body size, shape and
anatomy in their social organization with castes of workers foragers guards
courtiers and the queen: and in nest-building for their colonies. Ants however
are hardier than termites able to cope with even hotter and drier conditions and
to wander farther form the nest on food-finding missions. Some ant species for
example are known to venture into the surrounding hostile landscape for more
than 50 metres (164 ft.).
Foraging llymenopterons gather all kinds of food scraps to take back to the
colony and share out. llarvester ants (genus pogonomyrmex and other seeds of
dryland grasses and similar plants, which they store in piles in underground
granary like chambers. A single harvester ant worker can amass 20,000 tiny
seeds in one week which is about four per minute during daylight hours a
llerculean achievement.
Some of the strangest desert ants are the honey or honeypot species (genus
Allyrmecocytus and other genera) found mainly in the deserts of North America,
Africa and especially Australia specialized workers in the colony known as
repletes have evolved to act as living larders for both moisture and energy; As
the dry season approaches their bodies swell with and nectar foods delivered by
foragers. The repletes store their wares in the paert of the gut called the stomach
or corop so that their abdomes swell like amber-colored pearls to some 8 to 10
millimeters (0.4 in.) across. Too distended to move the repletes lie on the nest
floor or hang from its roof.
When moisture is scarce the repletes are literally tapped for food by other
workers in the colny. The workder pats the replete with its antennae and the
replete exudes some of its syrupy store which the worker then laps from its
mouth or anus. A large nest may have several hundered of these living food
stores usually in one of the deepest chambers. As the dry season fades the
repletes give up the lest of their sweet honeydew, In some species they then
resume normal nest duties while in others they simply perish and their bodies
are removed unceremonoiously from the nest.
While ants and termites have adapted well to the rigors of the desert, it is the
beetles (Coleoptera—the earth’s most prolific order of insects) that are the
supreme drought survivors, with many thousands of species eking out their
inconspicuous lives in the desert, quietly feeding and breeding. The majority
scurry across the surface soil in their search for small edible scraps of plant and
animal matter. A few beetle species, however, have higher profiles due to their
more predatory habits.
Among the most conspicuous is the thermophilic, or “heat-loving,” black
ground beetle—one of the few creatures out by day, walking over the scorching
surface in the blazing desert sun. It preys on other insects, grubs, and small
creatures, seizing and chopping them up with its outsize jaws. The beetle’s long
legs give a good turn of speed and hold its main body above the hot desert sand.
Hairs on the legs and feet detect vibrations both in the air, which could be an
approaching predator, and in the ground, which might be a hidden meal. If
challenged, the black ground beetle contorts its body around to spray a burning,
stinging fluid from its rear end at the enemy.
The jewel-bright scarab (Scarabaeus sacer)—a type of dung beetle—of the
Saharan edge was revered by the ancient Egyptians for its glistening colors and
held a key place in their cosmology—they thought of the sun as being rolled
though the sky by a giant scarab. The sacredness of the Saharan scarab was
perhaps an early recognition of the importance of all dung beetles in the ecology
of the desert. The recycling of animal droppings is especially important in the
dry desert soil, where dung on the surface quickly loses its moisture and
becomes too hard-baked and desiccated for the normal processes of microbial
decay.
Dung beetles (Scapabaeus, Canthon, Copris, and other genera) chew off balls
of the droppings and bury them in chambers below the desert surface, laying an
egg on each one. Once the beetle grub (larva) has hatched, it eats the dung,
which has become soft and edible after absorbing moisture from the surrounding
soil. The grub evacuates its own droppings underground, thereby taking the
breakdown and return of minerals and nutrients into the ground one stage
farther. The grubs also pupate underground and emerge as adult beetles at the
surface to continue their life cycle, leaving an enriched soil below.
Dung beetles have evolved to deal with the particular fecal matter of their
region. In Australia most of the local large mammal species, such as kangaroos,
are drought-adapted and so produce very dry solid wastes. The Australian dung
beetles, such as the genera Blackburnium or Bolboceros, thrive on this, and their
plump, white, C-shaped larvae, called curl grubs, are common even in dry
grassland and arid scrub. When cows and sheep were
introduced to these marginal pastures in the 19th century, the native beetles
shunned their moist droppings and other dung beetles had to be imported from
the homelands of the newcomers to maintain the ecological cleanup process.
Scorpions (order Scorpiones), eight-legged arthropods of the arachnid group,
are classic desert animals, enduring extremes of temperature that would kill
most other creatures, and can enter a state of inactivity or torpor during which
they need
no food or water for many weeks. Desert-dwelling scorpions are usually a sandy
color for camouflage, although most species hide by day in burrows or under
stones, emerging only at night to hunt. Their four pairs of simple eyes provide
only poor vision, and their main senses are touch and smell. The hairs on the
legs detect air current and vibrations, including sounds; the tiny time delay
between vibrations reaching the nearer leg compared to the farther one tells the
scorpion from which direction the sounds come. There are also featherlike parts
called pectines on the insect’s underside, not found in any other animal group,
and these are thought to pick up vibrations from the ground.
The Saharan androctonus (Androctonus australis) and Saharan buthus (Buthus
occitanus) are among the most poisonous of the scorpion order, injecting venom
from the sharp-tipped tail sting that can kill a human or a largish mammal. The
sting of the centruroides, or sculptured scorpion (Centruroides sculpturatus), of
No American deserts—yellow or yellow-brown with two dark back stripes—is
also potentially fatal. A threatened scorpion warns a potential aggressor by
flexing its tail, holding the sting at the ready and raising its outstretched pincers.
It may also, but does not always, use its poison on its prey. The scorpion grabs
the victim with its two large, pincerlike pedipalps and tears it apart with the
smaller but more powerful jawlike chelicerae. Large scorpions tackle insects,
spiders, centipedes, lizards, and even small mice and rats.
The adaptation of very potent venom is shared by many desert predators,
including desert spiders, snakes, and wasps. In the desert environment, where
prey is often scarce, powerful, fast-acting venoms not only improve the chances
of capture, but help to avoid a long pursuit through the dry heat. Toxins are used
for defense as well as attack, however, and a variety of small desert creatures,
including whip-scorpions, blister beetles, millipedes, and mites, spray out
distasteful, stinging, or burning secretions when in danger.
Velvet mites (family Thrombidiidae)—an arachnid about the size of housefly
with a red, velvety covering—wander the desert sand eating any scraps of plant
or animal matter they can find. Natural toxins in their bodies are so poisonous
that they can kill small carnivores such as grasshopper-mice that disturb or
attack them.