Marshall’s discovery was confirmed in a series of ingenious experiments. In one, his collaborator Ellen Thoms at the Cincinnati Zoo spray-painted molted tarantula exoskeletons gold to prepare them for study under an electron microscope, which revealed the fine structures of the hooks and filaments. In another experiment, Marshall shaved the legs of one of the giant arachnids. He knocked out his subject with CO2, removed some hairs with a razor, revived the beast, riled him, then listened for hissing. Then he shaved a little more. When the hissing stopped, he knew he had hit the right hairs.
The experiments went well beyond understanding the hairs themselves. They show that tarantulas evolved profoundly and rapidly to adapt to ecological challenges—unlike such living fossils as horseshoe crabs, which have remained unchanged for millions of years. The great challenge for tarantulas was probably the sudden appearance of burrow-dwelling, spider-hunting mammals, the forerunners of today’s skunks and possums. “Some tarantula ancestor evolved the urticating hairs, and it just went woof! It just took over,” Marshall says. “It’s one of the greatest evolutionary tales you can tell.”
Urticating hairs—those that provoke itching—evolved only in New World tarantulas, which reside in areas ranging from the South American tropics to as far north as Rolla, Missouri. About 500 of Earth’s 850 tarantula species live in the Americas. Of those, 460 have urticating hairs.
In the tropics, the hairs are not the perfect defense against the coatimundi, a long-snouted relative of the raccoon that can move fast enough to avoid the hairs. Wasps are another problem for tarantulas. Several varieties paralyze tarantulas with their sting and then lay eggs in the spider’s abdomen. When the eggs hatch, the paralyzed spider is eaten alive by wasp larvae. Even the goliath birdeater is not immune. The particular species of wasp that feeds on the goliath is the size of a sparrow.
Elsewhere, tarantulas without hairy weapons have had to make do with aggression. Marshall says tarantulas from Asia, Europe, Australia, and Africa can seem nasty-tempered. He tells a story about one tarantula in Australia that reared up and, waving its legs and gnashing its fangs, chased away a dog. Although a tarantula can’t kill humans, “the venom of Australian tarantulas is deadly to dogs,” Marshall says. “It’s one of those flukes of venom.”
When it’s feeding time at the spider lab, Marshall uses tweezers to seize a cricket hopping around the food terrarium, opens a tarantula container, and drops in the insect. The spider gravitates to it like metal to a magnet, then begins to chew and suck its food.
Although tarantulas are such eager eaters that they often eat each other, Marshall found that a female Tanzanian chestnut tarantula will put down its freshly killed prey and allow its young to feed instead. “They appear to sacrifice for their offspring,” Marshall says. “They defer eating themselves. They become anorexic. While the babies get fat, the mother shrinks.”
What’s more, some tarantula young appear to cooperate with one another at mealtime. With most spider species, the young push their siblings away from food. But in the Cameroon red tarantulas that Marshall describes in a forthcoming paper, spiderlings not only feed side by side without aggression but with their legs woven together. When Marshall saw this he realized: “They are huddle-feeding together. This is cooperation!”
A Memphis Zoo colleague, Steven Reichling, recorded a similarly striking behavior in a related species of African baboon spider, Hysterocrates crassipes. He noted that a female spider faced with another mother’s hungry babies did not try to kill or injure them—even when they annoyingly crawled up her legs and tried to eat her meal. In the company of suitors, females of this species also exhibited remarkable restraint: A male survived in a female’s enclosure for two months without being cannibalized and finally was removed without incident.
Even more surprising, in a presentation at the Ohio Academy of Science two years ago, two of Marshall’s undergraduate students demonstrated that Indian ornamental tarantulas—fast, high-strung spiders with bright black-and-yellow markings on their forelegs—usually choose to live with a sibling. Melissa Varrecchia and Barbara Vasquez offered 20 11-month-old tarantulas a choice of retreats: a tube in which a sibling had spun silk or an identical empty one. Fourteen chose their sibling’s tube.
Under Marshall’s tutelage, another undergraduate, Amanda Wiegand, discovered that an inch-long East African tarantula performs an elaborate courtship dance in which both the male and female participate. The male twitches and drums his legs, and the female responds by gracefully fanning her legs. The dance continues for several minutes before ending in copulation. It is the first case of tarantula courtship described by scientists.
Such findings have changed Marshall’s entire view of spiders. A year and a half ago he told a radio interviewer that the scientific paradigm he was taught for the life of a spider was simple: “They hatch, they grow, they live in the eternal now moment, and there’s really no role for experience shaping their behavior—they’re like little machines.” Now he has watched them for too long to believe that. “I’ve repeatedly seen tarantulas respond to my entering a room by moving to a different part of the cage or going into a retreat,” he says. “When you walk in the room, they know: Here comes this huge thing again.”
Furthermore, individual tarantulas exhibit individual quirks. “I’ve brought a lot of Theraphosa out [of the jungle] and into captivity,” Marshall says. “Some would settle down and adapt to the artificial habitat of a terrarium with a cave I provided, while others would pace and pace. It’s very clear to me that individual spiders can differ in how they respond to stimuli.”
Tarantula hobbyists have reported similar observations. One told Marshall how a tarantula methodically sorted the multicolored aquarium gravel in its tank into separate colors. Another had a female tarantula who learned to unscrew the lid to her container. He found her two days later in a stack of folded laundry.
“Personality is a heavy word to put on a bug,” Marshall says, “but if you define personality as individual behavior responses—well, I’ve had some spiders, tarantulas of the same species and from the same population, and I can take one out of a box and let it run over my hand, and I have others that just freak out and try to run away. A lot of that is individual variation in how they respond to being touched.” Still, he is not sure how far he can go with this notion. Tarantulas, he ponders, “probably know something about the area where they live, the landscape they live in, at some spidery level that we can only guess at. Long-lived, giant spiders have a lot more going on than we have any idea of.”