Dancing Cockatoos and the Dead Man Test by Marlene Zuk

Author:Marlene Zuk
Language: eng
Format: epub
Publisher: W. W. Norton & Company
Published: 2022-06-28T00:00:00+00:00

The Really, Really Itsy-Bitsy Spider

Octopuses have eight limbs, and we think they are sinuous and graceful. Spiders have eight limbs and we think they are horrid and creepy. This seems profoundly unfair. It is particularly unfair because in addition to being just as agile in their movements as the lauded octopuses, spiders show us the limitations of the nervous system, and just how the body limits the mind, or at least the way we behave.

Bill Eberhard is a biologist with the Smithsonian Tropical Research Institute and the University of Costa Rica, and he has always been ready to question invertebrate conventional wisdom. He tends to study animals that other people dismiss: earwigs, wasps that parasitize other insects, and, yes, spiders. His work on the latter has included spiders’ kinky sexual practices (he describes the sound that one species makes as “resembling squeaking leather,” which in an earlier book I said was like spider porn, if such a thing can be said to exist).23 He has also asked a question to which spiders are perfectly suited: Does being small mean they are dumb?

Many people have tried to make connections between brain size and behavior, especially intelligence, as I discussed in the previous chapter, but few have drawn this comparison out to its logical conclusion: Are there animals that are so tiny that they are almost, as the saying goes, too stupid to live, or at least to do complicated tasks, or tasks requiring flexible responses? Even Darwin wondered about this possibility, especially when faced with the complex behavior of ants; in his 1871 book The Descent of Man, and Selection in Relation to Sex, he mused, “The brain of an ant is one of the most marvelous atoms of matter in the world, perhaps more so than the brain of man.”24

How might such small-scale intelligence be possible? Do minuscule animals pay a price for their lack of brain capacity? Among vertebrates, smaller individuals tend to have larger brains relative to their body size, a generalization called Haller’s Rule, after Albrecht von Haller, an eighteenth-century Swiss physiologist. The rule seems to work for many invertebrates as well, but because neural tissue is expensive for an animal to maintain, it wasn’t clear if there is a lower limit to the evolution of brains capable of driving complex behavior. Very small animals may well have different constraints on the way their brains can manage their behavior, but few scientists have tried to apply Haller’s Rule to creatures without backbones.

Eberhard has studied the spider Anapisona simoni, the adults of which weigh less than a milligram. To put this in perspective, that is lighter than a single staple, or an inch of sewing thread. Yet inside their compact form is enough nervous tissue to enable the spiders to produce orb webs, the silky wheel that entraps even tinier prey. Eberhard wondered if the extremely difficult process of weaving a web was more of a challenge to the minuscule Anapisona than to three other spiders that weighed

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