by Joseph DeSisto
Night, and the Sonoran Desert comes to life. Lizards and mice emerge from their hideaways to eat, fight, and mate, while scorpions and giant centipedes scuttle about, hoping to stumble upon a juicy insect meal. All the while, a female tarantula waits in her burrow.
She has no need for sight or smell. She only has to feel — lines of silk trace the ground around her burrow, and she keeps her feet on these silk lines to feel every vibration. A pair of lizards chase each other, dangerously close to the burrow, and the spider flinches in predatory excitement, but bides her time. A few seconds later, a june beetle, weary from a night of flying, lands by the entrance and takes a few ill-fated steps. Crunch!
Tarantulas are found all over the tropics and subtropics, from rainforests to mountaintops to deserts. The blonde tarantulas of North America’s deserts, in the genus Aphonopelma, are some of the toughest and longest-lived arachnids on earth. Females reaching maturity after a decade, and can live another several years after that. The longest-lived specimen known to science survived for more than 17 years (Ibler et al. 2013).
The female blonde tarantula spends nearly her entire life underground, in a short vertical burrow. This burrow, and the patch of earth around it, is her entire world — for ten years or more she ambushes and feeds on beetles, scorpions, and other unlucky passers-by. As a result, females are seldom seen except by those curious enough to wander through the desert flipping large rock slabs and inspecting the bases of bushes.
During my trip to Arizona this summer, I only found one. I provoked her with a blade of grass, to see if she would leave her burrow. Even though her home was all but destroyed by my rock- flipping, this spider adamantly refused to leave. She held her ground, furiously biting and lashing out with her front legs.
Male blonde tarantulas are much more easily seen, and during my trip to Arizona I found several crossing roads at dusk. For the first one, I stopped and left my car to get a closer look, eager to see what this amazing creature was all about.
Tarantulas are big — this one had a leg-span approaching five inches. It was easy to coax him into a jar, since without a burrow to defend, blonde tarantulas are quite docile animals. Had I been a little braver, I probably could have picked him up without being bitten. If I had failed, the bite would have been painful, but no more dangerous than a bee sting.
Compared to the female tarantula, the male is leaner, with a smaller body and longer, skinnier legs. The sexes are also different in another respect: experiments have shown that when at rest, male blonde tarantulas can get by on significantly less oxygen than their mates (Shillington 2005).
There’s a good reason for that. At around ten years of age, while females remain in their burrows, males reach sexual maturity and begin the “wandering phase” of their lives. When he is ready to mate, a male blonde tarantula emerges from his burrow and strides off into the desert in search of a female.
The desert is a big and lonely place, and female tarantulas may be few and far between. Here a male’s athletic prowess comes in handy: males that can walk the longest and fastest without tiring are the most likely to find a not-yet-mated female. This is important, since a female who has already mated might prefer to eat him rather than entertain a second suitor.
During his walk-about, a male blonde tarantula faces many hazards, from spider-eating birds and wasps to the desiccating sun and wind. Nothing but death can dissuade a male from his journey. Texas tarantulas with radio transmitters have revealed that while some can get by traveling only a short distance, others may journey more than two miles over a period of several weeks (Stoltey and Shillington 2009).
My road-crossing specimen didn’t take to captivity very well. I provided him with plenty of room, soil and a place to hide, but all he could do was pace, back and forth across his cage. He did not eat or rest — he only walked. Finally I took pity and released him, and watched my eight-legged friend stumble back into the desert.
If a male blonde tarantula fails to find a mate, he will simply walk until he dies. If he does manage to reach a female’s lair, and he is lucky, she will mate with him. After, she might eat him, or she might not. It depends on how she’s feeling. The outcome hardly matters to the male. If she eats him, his body will be a final, nutritious gift to his offspring, yet to develop inside her. If she allows him to live, he will simply return to the surface, stretch his hairy legs, and keep walking.
Ibler B., P. Michalik, and K. Fischer. 2013. Factors affecting lifespan in bird-eating spiders (Arachnida: Mygalomorphae, Theraphosidae) — a multi-species approach. Zoologischer Anzeiger – A Journal of Comparative Zoology 253(2): 126-136.
Shillington C. 2005. Inter-sexual differences in resting metabolic rates in the Texas tarantula, Aphonopelma anax. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 142(4): 439-445.
Stoltey T. and C. Shillington. Metabolic rates and movements of the male tarantula Aphonopelma anax during the mating season. Canadian Journal of Zoology 87: 1210-1220.