An attractively marked spider conspicuous by the bright orange-red markings around the middle of each leg, hence its common name. The rest of the spider is predominantly dark brown in colour with a fawn brown ring around the head area or cephalothorax and similar colored bands on the legs below the ‘red knees’. As typical tarantulas, they have a heavy, robust body covered in short dark hairs. Some of these hairs can be flicked off by the back legs and act as irritants to the eyes and skin of predators. These ‘urticating’ hairs are also very effective against humans so, although this species is placid and rarely bites, handling can cause nasty skin reactions. Females are very long-lived with records in captivity of over 20 years at which stage the spider has a leg span of around 15-17cm.
Red-kneed tarantulas are restricted to the seasonally dry desert areas of western Mexico. They usually excavate burrows, often beneath other objects, in which they retire during the day as protection from the searing heat. The temperature and humidity in the burrow remains fairly constant even on the hottest days. Without this retreat, these spiders would rapidly succumb to the drying heat.
These true tarantulas are relatively slow-moving predators, often preferring to sit and wait in ambush just inside the entrance to their burrow for a passing meal. Insects, scorpions and other spiders make up the bulk of the diet, although the spider is powerful enough to catch and kill reptiles, frogs and even small birds and mammals.
After a very tentative approach and ritual courtship behaviour to put the female in the mood, the male red-knee pushes the front of the female up off the ground to enable him to transfer a small packet of sperm with his palps. Females have two sperm storage sacs called spermathecae where she retains the male’s contribution until the eggs are laid. It is only at this time that the eggs are fertilized. In red-knees mating usually takes place in autumn with the eggs being laid the following spring. One female may lay up to a 1,000 eggs in one clutch.