The Tarantula, Reappraised

News and commentary about environmental issues.
March 20 2012 12:55 PM

Hairy Cannibals

The tarantula, reappraised.

Tarantula.
Tarantula

Hemera Technologies.

More revolting creatures: the eel, the centipede, the skunk, the snapping turtle, the vulture, the tick, the jellyfish, the hyena, the slug, and the mosquito.

Movies have failed miserably at enlightening the public about tarantulas. Case in point: a villain in the first James Bond movie (Dr. No) puts a tarantula in our hero's bed. As Bond wakes to see the stocky black spider crawling on his shoulder he appears to be sweating heavily—presumably because this creature could kill him.

But the tarantula's bite is no more deadly than a bee sting. It was never the spider’s intention to bite Sean Connery, obviously too big to eat. The creature’s small mind was on how to get back to its familiar burrow, and Bond had more to fear from the cigarettes he smoked. (It was 1962.)

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Tarantula venom serves to subdue small prey—mainly insects; it actually takes considerable effort to get a tarantula to bite a human being. We know that thanks to the considerable efforts of the late Dr. William J. Baerg, who, while a member of the University of Arkansas entomology department during the 1940s, laboriously persuaded many tarantulas to bite him. The first attack was unbidden and occurred when the doctor tried to position a Trinidadian tarantula (Avicularia velutina: “extremely pugnacious in attitude,” he wrote, “it at first impressed me as probably venomous”) to bite a white rat. The spider went for his finger instead. Contrary to the prevailing wisdom, he learned that the sting, though irritating, was basically harmless. More deliberate attempts soon followed with 26 less pugnacious tarantula species. Baerg had to repeatedly prod them to bite. (For comparison’s sake, he also allowed himself to be bitten by the smaller and less scary-looking black widow spider, and got very sick.)

Of course it’s the tarantula's size and disconcerting hairiness that lead us to our prejudice. The biggest of the 932 named tarantula species, the Goliath bird spider of South America, is almost a foot across—an undeniably impressive specimen that can eat small vertebrates. (It is itself eaten, said to taste like shrimp.) At the other end of the scale is one (Aphonopelma paloma) with a body length of 8 mm, about 1/3 of an inch. About one-fifth of all spiders are tarantulas.

There is no record of any human being ever being killed by the sting of a tarantula, large or small. (There may be an unrecorded serious outcome somewhere for a person allergic to stings of any kind, or someone who suffered a bacterial infection from an untreated bite.) In any case the chances of a North American coming fact-to-face with a tarantula, let alone being bitten, are small. Tarantulas live in tropical or semi-tropical regions, and deserts around the world. In the U.S. there are about 40 species, mostly in Southwestern deserts, and none east of the Mississippi. (Some of the arboreal species, from Asia and South America, are faster-moving and pack a more painful bite.)

In late summer in the desert it is possible, though not common, to see males on the move seeking females. But most of the time the North American tarantulas stay out of people’s way, emerging from their burrows after dusk and retreating at dawn. Unfairly maligned by the public, the tarantula has also been looked down on by entomologists. Beside the orb-weavers like the famous Charlotte, tarantulas seem primitive, clumsy, and less than inspired in their silk work. Their name isn’t even their own—it comes from the European wolf spider (Lycosa tarantula), a different hairy creature. When Europeans came across new types of spiders in the Tropics, they designated any large, fuzzy ones as a kind of tarantula. It’s more accurate to call them Therasophids.

The startling hairiness is useful, an excellent adaptation for a creature with terrible eyesight. (Unfair that they have eight eyes, and not one works well.) Tarantulas’ hairs are sensitive to air movement, allowing them to detect something as subtle as the breeze caused by a cricket passing by, and to vibration, alerting them to a potential mate drumming on the ground off in the distance.

Another kind of hair acts as a line of defense, short of biting, for many New World spiders. When threatened these tarantulas use their legs to rake small, barbed hairs off the tops of their bellies. The hair defense is adapted to irritate the nasal passages and eyes of a mouse. Dr. Baerg’s wife Eloise, a good sport, got a temporary rash when she exposed her arm to a cloud of the hairs; other human beings approaching an agitated tarantula report inflamed eyes.

The tarantula does not stalk; it waits to sense something edible passing by. A female may spend her life, up to 30 years, within a couple of feet of her first home. In fact, tarantulas, the terrestrial ones anyway, are among the most sedentary of creatures. If James Bond's chest appeared moist in the spider scene from Dr. No, that's because an off-screen insect wrangler was misting the animal to make it crawl. (Tarantulas are extremely sensitive to water spray and air currents.)

When dinner wanders by, the spider seizes its prey—crickets, grasshoppers, beetles, flies, and roaches—with its short forelegs, known as pedipalps, and then impales it with upraised fangs. The venom at the tip of the fangs stuns or kills the future meal. Up close, or magnified, it is a scary technique.

It takes many hours to deconstruct and dissolve a cricket or, in the case of the large Mexican tarantulas, a crayfish, small frog, lizard, snake, or even a dead fish. It’s not a pretty process. The spiders use limbs close to their mouths to macerate the victim, then drool out enzymes to break it down. The resulting soupy solution of partially digested prey is drawn back through the mouth by the tarantula’s sucking stomach.

Though they don’t create beautiful webs, tarantulas do make silk. They can wrap their prey to eat later, and some kinds of tarantulas use sticky silk to gather up soil and move it around as they remodel their homes.

Silk is also sexy. The male uses a sheet as a sort of pillow for his seminal fluid. He then dips the points of his palpal bulbs—black organs at the end of his pedipalps, into the fluid until the bulbs are filled.

The actual process of insemination is tricky, and can turn tragic. The drama begins when the male approaches the lip of the burrow and announces his desire by drumming his front legs on the ground. If the female is in the mood, she’ll drum back.

When he comes near, she’s likely to charge out of her burrow looking threatening. If she’s not feeling cooperative, she will kill him and eat him.

Otherwise, the male taps her on the back and, if receptive, she rises on her hind legs and spreads her fangs. The male tarantula uses the handy spurs on his forelegs to lock those fangs, and then hoists her up to get access to her genital region—the epigastric furrow. If he doesn’t get a good grip, she may kill him. If he’s skilled enough to manage a secure hold, he still has some legs free to stroke her belly, an act that is said to induce a trance, certainly a desirable state. He then inserts each sperm-laden palpal bulb into the female’s genital opening. The mating process would seem to select for males with upper body strength combined with massage expertise. (Just like humans.)

The act complete, he releases one of her fangs, then the other, and backs off promptly. Sperm can remain in the female’s receptacle until the following summer when she produces the eggs. Fertilization occurs as the eggs are being laid, not internally.

Tarantula lovers can get a little dewy-eyed watching the female care for her egg sac, which contains 500 to 1,000 eggs and is made from her silk. (From egg laying to emergence takes 45 to 65 days.) She rolls it out of the entrance of the burrow to warm in the sun, and either sits over it like a hen on her eggs or keeps one or two feet on the cocoon so she can pull it back inside when something comes near. The maternal protective behavior is not dependable; if she’s disturbed or the sac is not viable the mother spider may extract the young and eat them.

Safely hatched young stay within the birth burrow for several weeks. Baby tarantula mortality is high because the young may eat each other at that point, and their mother will eat them if they stay with her too long.

The spiderlings depart, not by ballooning—sending silken threads out to catch an air current in kite fashion—as the orb weavers do, but on foot, with a slow, dignified gait. If they didn't split up as they dispersed, they’d eat each other.

Sure, they’re cannibals, but there are aspects of tarantula life that inspire sympathy, like molting. As the spider grows it undergoes sequential molts, getting a larger exoskeleton each time. The separation of the old exoskeleton happens when fluid is secreted into the gap between the old and the underlying new body. During the hours of molting the spider’s crucial sensitivity to sounds and motion is suspended, rendering it vulnerable to predators. Before hardening in the air, the new skin can tear and cause the spider to die from loss of blood. The male molts for the last time when he matures but the female continues to molt annually as long as she lives. On the plus side of the ordeal, a lost limb can be regenerated over successive molts.

The tarantulas may be baby-eaters and sibling eaters and husband-killers, but the truly ghastly actor in this story is the Pompilid or Sphecid wasp, a spider's worst enemy. Attacked, the tarantula rears up to show its fangs—in this case a poor strategy. The wasp injects paralyzing poison in the spider’s belly and drags the motionless beast to a hole. There the mother wasp lays an egg on the spider’s abdomen, ensuring fresh meat for her offspring. The hatched larva consumes the living, paralyzed tarantula.

Back to Dr. Baerg, who was willing to risk his life to demonstrate that tarantulas are no threat to humans. He retired from teaching in 1951, publishing The Tarantula in 1958. Somehow the screenwriters for Dr. No, at work a few years later, missed the information in his charming book, and especially his sensible summary: "To anyone who has learned to know this spider, it is as handsome as a goldfinch and fully as interesting.”

Constance Casey is a former New York City Department of Parks gardener and writes the monthly "Species" column for Landscape Architecture Magazine.

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