This Spider Can Hide Underwater From Predators for 30 Minutes

When faced with human predators, a large tropical spider heads underwater.

A long-legged water spider called Trechalea extensa escapes from threats by fleeing and using a film of air to stay safe in the water for as long as 30 minutes.

Researchers observed the impressive behavior of the spider, which is typically found from Mexico to Panama.

Study author Lindsey Swierk, assistant research professor at Binghamton University in New York, had previously studied a Costa-Rican lizard species that were able to stay underwater for 16 minutes in order to hide from predators.

This time around she was at a research site in Costa Rica with researcher Patricia Esquete of the University of Aveiro in Portugal. Esquete and her student have been studying the ecology of the spider for several years.

“My own expertise is lizard ecology, specifically the diving semi-aquatic anoles,” Swierk tells Treehugger. “When Dr. Esquete and I witnessed a Trechalea spider fleeing underwater, we were excited to document this as another instance of small Neotropical organisms using diving as an escape method.”

Their findings were published in the journal Ethology.

A Film of Air

When the spider first spotted the humans, it tried to run away by running on the surface of the water, which is a common escape mechanism for these spiders.

“Even though the water in the stream is quickly moving, this is a viable strategy for these spiders,” Swierk says. “As we continued our approach, though, the spider dove underwater.”

The spider spent just over 30 minutes underwater. While it was submerged, it had a kind of film of air over its whole body. The researchers believe that the fuzzy hairs on its body act as a shield, holding up the film of air.

That film of air might work to keep the openings in the spider’s respiratory system away from water so they can still breathe. It might also help keep the spider’s body warm underwater while it sits submerged in a cold stream.

“For a lot of species, getting wet and cold is almost as risky to survival as dealing with their predators, to begin with,” said Swierk. 

Unlike humans, ectotherms like spiders rely on external heat sources, like the sun or a warm rock, in order to regulate their body temperatures.

“In environments where external sources of heat can be hard to find, getting cold can be risky,” Swierk says. “Colder animals are often slower, digest their food less well, and are more vulnerable to predators.”

Risk Assessment

Researchers aren’t sure how unusual this coping mechanism is for spiders looking for a way to avoid threats.

“We don't know how widespread this method of escape is among spiders,” Swierk says. “We do know that, for many species, it may be likely to be a last resort, since it probably also comes with some physiological costs.”

Any animal hiding from a predator has to deal with risks. There’s always a danger when running away. It might mean leaving other animals or the territory unprotected. Or they could expend a lot of stored energy in the physical act of fleeing.

For these spiders, the risk is losing body heat and breathing issues, says Swierk, who explains why she finds the research fascinating.

“Discovering new behaviors like this in animals highlights how evolution has diversified traits like antipredator strategies in light of an animal's ecology,” says Swierk. “This can give us insight into the process of evolution, and possibly how animals adapt to new environments.”