Ferns that appeared brown and dead during the summer suddenly abound, green and glorious among the rocks.
Spring, summer, fall and winter. In most parts of the country, people settle for four seasons. Here in the Chihuahuan Desert region, we dream, hope and talk constantly about our fifth season – the rainy season. Local wags will tell you that the fifth season starts on July 4th – with a crash of thunder, a gust of wind and a torrential downpour that causes Independence Day celebrants to scurry for cover and ranchers to sigh in relief.
The sighs of relief are due to the fact that, in the Chihuahuan Desert, up to 75 percent of our annual precipitation falls in the summer months. This gift from the heavens results in a frenzy of friskiness as our plant and animal neighbors get on with the business of life.
The first hard rain of the season brings out thousands of fuzzy, bright red velvet mites. They emerge from the soil with only one goal in mind – find a mate. The male velvet mite does most of the work in this timeless dance. He’s a gardener by nature, creating a “sperm garden” on small bits of plant material. But gardens need admirers, so he lays an elaborate silk pathway that radiates out from his sperm garden. If a female encounters the path and finds it appropriately enticing, she’ll follow it to the sperm deposit and sit in the sperm, thus impregnating herself.
Male two-tailed swallowtails gather sodium from rain puddles that they pass on to females during mating.
The female velvet mite can lay up to 100,000 eggs. The larvae from these eggs attach them- selves to grasshoppers, beetles, butterflies and other arthropods. They get their nutrients by sucking the juices out of their unlucky hosts. After the larvae mature, they return to the soil, where they feed on insect and snail eggs and other tiny arthropods – until the first hard rain of next year, when they emerge to start the cycle all over again.
The rumble of thunder can bring another desert inhabitant to the surface for a frenzy of breeding and feeding. The small spadefoot toad spends most of the year buried in the ground where it can avoid the hot and dry conditions of the desert surface. But vibrations caused by thunder indicate to the toad that moist conditions exist, and the toads begin to emerge in mass. The males seek temporary pools and puddles of water where they immediately send up a deafening breeding chorus, a come-hither call for any female within a half-mile radius.
After breeding, the female lays 3,000 to 5,000 eggs at a time, and the race for survival begins. The eggs must hatch and the larvae must pass through the aquatic tadpole stage before their puddle of water dries up under the heat of the desert sun. Eggs typically hatch in about 36 hours, and the tadpoles metamorphose into juveniles within eight to 10 days of hatching.
While on the surface, the spadefoot toads feed on protein-rich insects that swarm with the coming of the rains. A few good meals increase the fat supplies of the toad enough to allow them to bur- row deep into the desert soil and patiently await the thunder of the next rainy season.
Other creatures are drawn to the damp soil left behind by a passing thunderstorm. Male butter- flies – especially swallowtails, sulphurs and tiny blues – gather in masses at damp patches of earth, sipping the salts dissolved by the rainwater. If disturbed, they’ll burst into the air, swirling around the puddle and eventually returning to continue their feast.
This behavior, known as puddling, is believed to enhance the attractiveness of the male and the reproduction success of the female butterflies. Females lose a lot of sodium during the egg-lay- ing process. But they’re too busy nectaring and laying eggs to replace it by spending time hanging around the nearest mud puddle sipping sodium. Instead, they compensate for the loss of minerals by receiving a “nuptial gift” of sodium from the male during mating.
Of course, insects and toads aren’t the only ones to feel a little frisky during the rainy season. Summer rains bring out the very best in our desert plants – especially the ferns. Ferns aren’t usually the first thing that you think of when someone mentions desert plants, but they should be. Take a peak along rocky cliff faces that face north or east. Seek out shady canyons or explore the cracks between large rocks. You’re sure to find one of the 78 species of ferns that calls the desert home.
For most of the year, our xeric-adapted ferns may not look like much. In fact, they’ll probably look dead. Gone. A victim of Mother Nature. Curled tightly in upon themselves, the fronds are brown and crispy. Dry as the desert itself.
But give the ferns a little water and the fronds miraculously come to life – often unfurling and turning green overnight. This ability to resurrect from the (seemingly) dead is one of those wonderful adaptations that makes ferns so successful. Special cells on the upper surface of the fern’s frond absorb water when it’s available and collapse (causing the fern to curl) as conditions become drier.
Most plants can lose about 25 percent of their moisture content before they begin to wilt and need water. The amazing ferns? They can lose up to 94 percent of their water content while waiting patiently for the next rain.
Some plants, according to old wives’ tales, can even be used to predict the beginning of the rainy season. The cenizo, often called the barometer bush, is said to put on a stunning dis- play of purple to pink blossoms to announce the coming of the rainy season. Not so fast, say the experts. Cenizo are most likely to bloom immediately after a rain in response to the high humidity and increased soil moisture. Although – those same experts will admit – the cenizo can bloom in response to high humidity even before the rains begin. So the old wives aren’t totally misleading us.
In the spring, hundreds of visitors arrive at the Chihuahuan Desert Nature Center having just traveled through the glorious bluebonnets and paint- brushes of Central Texas. The golden browns of our winter- dry grasses don’t impress them. In fact, they feel bad for us. “We’re so sorry,” they say, “that you’re having such a terrible drought.” It takes a golden tongue to convince them to come back in the summer when the rains bring out the very best of our wildflowers.
Scarlet bouvardia and yellowbells splash the rocky hill- sides with yellow and brilliant red flowers framed by deep green leaves. The beebrush, with its insignificant white blossoms, fills the canyons with the most exquisite fragrance on still summer nights.
But shrubs, while showy, aren’t our only wildflowers. The sunset-orange of a flameflower or the tangle of tiny pink spider- lings and sky-blue morning glories will question your whole sense of what a “natural color” really is.
Invite a friend to visit the Chihuahuan Desert region in August, and they’re likely to tell you that you’re nuts. Visit a desert in the summer? No way. But if you can convince them that our fifth season is the most spectacular, they’re likely to never go home.
by Cathryn A. Hoyt, Fourth Quarter 2010 issue
Cathryn Hoyt, Ph.D., executive director of the Chihuahuan Desert Research Institute, is an archeologist and paleoecologist. e-mail: firstname.lastname@example.org