Heat and dryness are facts of existence in West Texas. Every living thing must either evade these conditions or adapt to them. Humans, through technology, attempt to create our own environment. We live in air-conditioned houses and drive an air-conditioned car to our air-conditioned offices. But what about other creatures? How do they cope with the West Texas heat?
The most common mammals of west Texas are burrowing animals. They spend daylight hours staying quiet within deep, cool living quarters where the earth itself insulates against the dry heat of the sun. Humidity within the burrow may be up to five times that in the outside air, and temperatures remain at 55 degrees after the first two feet of tunnel. Burrowing mammals, which emerge to feed at twilight include prairie dogs, kangaroo rats, badgers and ground squirrels. A common sound on a hot summer afternoon is the high trill of a ground squirrel when it comes momentarily out of its burrow to inspect its surroundings. This peaceful call seems to express contentment with the environment and confidence that the cool evening is not far off.
Larger mammals rest during the hot daytime hours in the shade of brushy thickets. Jackrabbits scratch out a "form" at the base of a shrub. This form may be six or eight inches deep, thus taking advantage of the cooler underground temperatures. Coyotes sometimes usurp the den of a badger, and possibly foxes do also. But foxes are not strictly nocturnal in our climate and are often seen during the daytime. They may have a greater tolerance of heat than other mammals. Foxes seen in daylight are often high in a tree in a draw, taking advantage of the cooling effects of the ever-present breeze.
Many insects of this area are also terrestrial. Ants are not particularly adapted anatomically or physiologically for this hot dry environment, but they survive by digging their tunnels deep within the ground. Ant tunnels have been revealed eight feet deep in excavations for highways or foundations.
Most crickets live in galleries that they dig in the soil. Their songs and chirrups are a delight to hear in the cool of the evening.
It’s surprising to learn that bees and wasps in this area are also burrowers. Many species dig holes or short tunnels at the end of which they deposit paralyzed insects or spiders and lay their eggs upon this food supply. Sometimes even on a hard-packed caliche or dirt road, hundreds of bees excavate burrows, as well in the hard pan soils of pastures.
Whether or not burrowing habits evolved in insects as an adaptation to escape heat, it’s certainly true that insects that live at least part of their lives in subterranean homes are much more able to survive the heat. The insects best adapted to life in extreme heat are beetles. In addition to their burrowing habits, many have developed leathery or horny wing-covers which, when closed over the back, enclose an air space which serves as insulation and reduces the amount of water lost through transpiration. Because of this protection, beetles are as likely to be diurnal as nocturnal.
Lizards are well adapted for life in a hot dry environment. Their dry scaled or plated skin is heavy and resists moisture loss. Their diet consists mainly of juicy insects, which provide all the liquid they need. They are poikilothermic - or cold-blooded - which means that they take their body temperature from the environment. This doesn’t mean they can stand unlimited heat, but they can tolerate a body temperature of up to 108 degrees.
Ground squirrels both hibernate and aestivate - that is, they remains underground all year, except for a brief period in spring and early summer! Many people do essentially the same thing - the weather is always either too hot or too cold, so we remain in our air-conditioned and heated homes having no contact whatever with nature. We should remember that the first great civilizations all developed in the arid regions of the world, and that Homo sapiens is as well adapted to heat and dryness as mesquite, foxes, cicadas, and lizards.
Nature Notes is sponsored by the Dixon Water Foundation and is produced by KRTS Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Burr Williams of the Sibley Nature Center.
