Tarantulas

NPS/Wayne Backowski

Autumn provides a brief glimpse into the workings of nature in the desert. At no other time is the intimate connection between life and death represented so clearly.

One of the species that best embodies this relationship between life and death is the desert tarantula, Aphonopelma iodium. Tarantulas, the largest spiders in North America, are typically two to three inches long and are covered with thousands of fine hairs ranging in color from tan to dark brown. Besides its eight legs, the basic sections of a tarantula's body are its cephalothorax (a fused head and thorax, or chest) and its abdomen.

Predators
Many tarantulas have a bald spot on the abdomen as a result of a unique defensive behavior. When cornered by a predator, the tarantula will rub its hind legs over its abdomen, brushing hairs into its enemy's eyes. Tarantulas have many natural predators including larger lizards, snakes, and birds. However, the most ferocious is the tarantula hawk, a large, metallic blue and orange wasp. A single tarantula hawk can sting and paralyze a tarantula, drag the spider back to a prepared burrow, and lay eggs upon the still-living creature's abdomen. The wasp then seals its paralyzed prey inside the burrow. Upon hatching, the wasp larvae will eat the tarantula alive. Although this outcome may seem grisly from our human perspective, nature knows only one standard: survival.

Mating
When a male tarantula reaches sexual maturity, between eight and ten years of age, he begins a journey that will both aid the survival of his species and cost him his life. Should you observe a desert tarantula in Joshua Tree National Park this autumn, it is likely to be a male in search of a mate. The male follows the scent of a female tarantula to the receptive female's burrow, which she has typically excavated in dry, sandy soil and lined with silk webbing. Tarantulas are solitary animals; there is only one spider in this burrow.

To alert the female of his presence, the male taps one of his legs against the ground until the female emerges. The male must then participate in a dangerous mating dance, wherein he fends off the female, who wishes to devour him, by using hooks on his front legs. His death will give the female a needed boost of nutrition, as she must now produce 500 to 1,000 eggs and a silk cocoon where the eggs will be protected. Even if the male escapes being eaten by the female, he will still die within a few months. Females, on the other hand, often produce eggs for 25 years or more.

Hunting
When not involved in the ritual of reproduction, tarantulas typically do not eat each other. Insects like beetles and grasshoppers make up a good portion of the tarantula diet, and tarantulas in the desert may also devour small lizards, mice, and even scorpions. Although tarantulas have the ability to spin silk, they chase down their prey rather than snaring it in webs. Their eight closely set eyes are not useful in hunting. Instead, thousands of sensitive hairs on the spider's body allow it to detect subtle movements in its immediate environment and "home in" on a victim. The tarantula strikes with its fangs, injecting venom. There is a struggle while the venom takes effect, and the tarantula must grasp its prey with the palps, two arm-like appendages between the mouth and legs. If successful, the tarantula wads up its semi-paralyzed victim, secretes digestive juices onto it, and sucks up the liquefied prey. One creature's death leads to another's survival; the pattern of life in the desert continues.

If you encounter a tarantula, take time to observe its body, its behavior, and its connection to the fabric of desert life, but please do not disturb this delicate connection. Wildlife should never be touched, chased, or fed, and the tarantula is no exception. Contrary to appearance and reputation, the tarantula is a timid creature and will not bite human beings unless seriously provoked. Like all animals in Joshua Tree National Park, the desert tarantula deserves our respect, not just for surviving, but for thriving in a place where the boundary between life and death is always shifting.

by Park Ranger Mike Cipra