Humans aren’t the only actors on the planet. To avoid being eaten, the ant-mimicking jumping spider pretends to be an ant, according to Cornell research published July 12 in Proceedings of the Royal Society B.
Ants are aggressive at defending themselves: They are well-armed with bites and stings and formic acid. Ant-mimicking jumping spiders (Myrmarachne formicaria), in contrast, can’t do much more than run on their eight legs when attacked. Not surprisingly, insect predators tend to prefer spiders over ants, so appearing to be an ant confers significant protection.
Protective mimicry is a remarkable example of adaptive evolution: Moths can be colored like butterflies, and grasshoppers may look like tiger beetles. While most mimicry studies focus on traits like color and shape, the researchers used multiple high-speed cameras and behavioral experiments to pinpoint how the spider’s movements mimic ants.
The video reveals that ant-mimicking spiders walk using all eight legs but pause frequently to raise their forelegs to mimic ant antennae. When walking, they take winding trajectories of about five to 10 body lengths, which made them look like ants following pheromone trails. While the researchers could see what the spiders were doing thanks to their high-speed cameras, many potential predators have slower visual systems, so that to them the mimics appear to be moving just like an ant would.
The researchers’ behavioral experiments showed video animations of ants, mimics and non-mimetic jumping spiders to large predatory jumping spiders. They report that “non-mimetic jumping spiders were attacked 4.5 times more than ant targets and three times more than mimic targets. There was no significant difference between the number of attacks on ants and mimics."
The researchers note that the findings “highlight the importance of dynamic behaviors and observer perception in mimicry.”
The research was conducted at Cornell by Paul S. Shamble, now a John Harvard Distinguished Science Fellow at Harvard University; Ron R. Hoy, professor of neurobiology and behavior at Cornell; Itai Cohen, professor of physics at Cornell; and Tsevi Beatus, now a professor of computer science and engineering at Hebrew University of Jerusalem.
Linda B. Glaser is a staff writer for the College of Arts and Sciences.