Mimicking ants is a good defense option because they do not make for good eating; ants often have spiny defenses and biting mandibles (and they're not afraid to fight back), and many also carry chemical repellants or venom. Though the focal spider of this study—Siler collingwoodi—was already known to move in an ant-like fashion, the researchers wanted to know how accurate its mimicry is, whether it mimics more than one ant species, and how effective this mimicry is at discouraging predators.

The research team also explored the role of the spider's brilliant coloration. "Unlike typical ant-mimicking spiders that mimic the brown or black body color of ants, S. collingwoodi has brilliant body coloration," says first author Hua Zeng, an ecologist at Peking University. "From a human's perspective, it seems to blend well with plants in its environment, but we wanted to test whether their body coloration served as camouflage to protect against predators."

To understand how ant-mimicry helps these spiders avoid being eaten, the researchers collected wild ant-mimicking spiders from four geographic locations in southern Hainan, China, and brought them back to the lab. For comparison, they also collected another type of jumping spider that doesn't mimic ants, as well as five co-occurring ant species that they thought might serve as models.

Back in the lab, the researchers characterized and compared how the ants and spiders moved in terms of how they used individual limbs, as well as their speed, acceleration, and whether they followed a straight path or took a more tortuous trajectory.