Tests on one toxin indicate that it kills insects quickly but has no impact on the cells of humans or other mammals. That, combined with some cardiovascular effects, is usually what kills you. This overstimulation of the peripheral nervous system also affects the glands, so that victims produce profuse amounts of sweat, saliva, tears and fluid in the lungs. Strangely, the only mammals this neurotoxin is known to affect are primates, which lack a substance in their blood that inactivates the venom. No one knows why primates are missing this protective substance.
Experts regard it simply as a quirk of nature.
That explains why Kirkwood has so much trouble finding these spiders when we go looking for them. It is very hot and dry, as it has been most of this summer. Just as we are about to give up, Kirkwood finds fresh silk. He explains that the long webs that extend down into the burrows give the spiders a surface across which they can maneuver more easily than dirt. Excited, Kirkwood digs down about a foot, exposing a large main burrow with several side chambers containing juveniles.