Despite their young age, baby spiders have a vision nearly as good as their parents. This enables them to be effective hunters early in their life, according to a new study.
The study, published in the journal Vision Research, helped explain how baby spiders, animals about the size of a bread crumb, can fit all the complex architecture of adult eyes into a much tinier package.
“Spiderlings can adopt prey-specific hunting strategies. They can solve problems,” said Nathan Morehouse, a biologist with the University of Cincinnati. “We thought the adults were pressing the limits of what was physically possible with vision. And then you have babies that are a hundredth that size.”
According to the research, baby spiders have the same number of photoreceptors as adults but packed differently to fit in a smaller space. They have 8.000 photoreceptors, but they’re smaller than the ones found in adults. Each of them is located next to each other to maintain the visual acuity that helps spiders distinguish objects at a distance.
The experts at the University of Cincinnati developed their own custom-made micro-ophthalmoscope, similar to those used eye doctors, to peer into the tiny eyes of baby spiders. They used the equipment to map the light-sensitive cells and their interaction.
“It’s a powerful, one-of-a-kind research tool that allows us to engage in several exciting projects that were not possible before,” UC biologist Elke Buschbeck said.
At the same time, they conducted a microscopic analysis of the tissues inside the spider eyes. Like most creatures in the animal kingdom, jumping spiders begin life with eyes that are much larger in proportion to the rest of their bodies. They have an extraordinary vision, such as tetrachromacy, the ability to see four colors.
“People say, ‘That’s going to be a big dog’ because of the size of the puppy’s feet. A puppy grows into its feet in the same way that jumping spiders grow into their eyes,” Morehouse said.
While having a vision almost as good as adults, baby spiders’ eyes do have one drawback, the research showed: they capture less light than those of the adults. That means they can’t see as well in dim conditions. This makes baby spiders conspicuous to field researchers working in the dark understory, he said.
“One thing you pick up on is spiderlings act a little drunk. They’re a bit stumbly,” he said. “They seem a little impaired. And it’s probably because the world is a little dimmer like you’re walking through the house with the lights off bumping your shins on the furniture.”
