Morehouse will use a $2 million National Science Foundation grant to study spider vision around the world. But for this study, he didn’t have to go far. He and his students collected mimic spiders by spreading a sheet under trees and whacking limbs at UC’s wooded Center for Field Studies a few miles off campus.
Spiders occupy a three-dimensional world. But whether they’re on the ground or climbing a tree, potential predators are likely to get a dorsal view, he said.
“Thinking of vantage point is essential,” Morehouse said. “From the top juveniles and adults both look like ants. And juvenile spiders look very much like ants from the side. But adult spiders shift away from the ant profile toward a more traditional spider-like profile.”
But it’s not enough to look like an ant, Morehouse said. To fool clever predators, you have to act like one, too. The spiders have enormous back legs like ants. Spiders have an extra pair of legs compared to ants and no antennae. But ant mimics will wave their small forelegs in the air like ant antennae.
“The level of mimicry we encounter in jumping spiders is incredibly detailed,” he said. “When ants follow a trail, they weave their heads back and forth. The ant is trying to cast back and forth over a chemical trail that’s hard to find.
“Remarkably, jumping spiders also perform this weaving behavior even though it has no functional significance for them,” Morehouse said. “They’re trying to be convincing actors. They’re trying to look like an ant.”