Chilean Rose Tarantula

Two Joints Without Extensors

Spiders have flexor muscles to pull their legs in, but a 1957 study of spider leg muscles confirmed that they have no extensor muscles at two of their leg joints. The study raised the possibility that the flexors there work against the spider’s own blood pressure, so that haemolymph, the fluid inside its body, would do the straightening a muscle normally does.

A Tiny Oxygen Gradient A Chilean rose tarantula’s lungs are so refined that a difference in oxygen partial pressure of just 0.12 to 0.16 kilopascals across the lung barrier covers its resting oxygen needs, against about 7.5 kilopascals that mammals require.

Built to Wait, Built to Molt

This is a medium-sized tarantula that lives on the ground. Females average a leg span of 12 to 13 centimeters and males about 9 centimeters, though males have proportionally longer legs. Females live up to twenty years in human care, far outliving males, which die within a few months of mating.

Among spiders it counts as large, at more than 14 grams. Its metabolic rate is 63 percent of the value expected for other spiders of its body mass, and researchers have recorded that rate dropping at 30°C when it is deprived of food.

To grow, it must go through several molts, and spiderlings molt five or six times in their first year. The species is native to desert and scrub habitat across Chile, Argentina, and Bolivia, where it hunts at night. It feeds on a variety of invertebrates as well as small vertebrates such as mice, frogs, and lizards, relying on its size to subdue them.

The Bristle Defense

It can throw irritating hairs from its body in defense, and doctors studying tarantula bites note that New World species like this one typically cause injuries to people through their urticating hairs, which can penetrate skin and mucous membranes and cause local tissue reactions. The hairs appear rose-colored on Grammostola rosea, which is where the “Chilean rose” name comes from.

Forty-Eight Toxin-Like Peptides

Scientists sequencing genes from Grammostola rosea venom glands predicted forty-eight new toxin-like peptides from the sequences. One of them, GTx1-15, inhibits one voltage-dependent calcium channel and two voltage-dependent sodium channels. Doctors reporting a bite from this species that left a woman with weeks of cramping note that trouble with both kinds of channel could affect muscle contractions.