Members of little-known family of spiders are the size of a mere pencil tip, yet they are formidable predators—and incredibly fast ones. A new study has documented these spiders snapping up prey at speeds the likes of which have never before been seen in arachnids.
Surprisingly, the diminutive hunters’ record-setting ballistic attack strategy independently evolved at least four times, according to research published today in Current Biology.
“These are the fastest-known arachnids so far,” says the study’s lead author, Hannah Wood, curator of spiders at the Smithsonian’s National Museum of Natural History. And they are the only ones known to catch prey in a way similar to trap-jaw ants. As such, Wood is calling these spiders, from the family Mecysmaucheniidae, “trap-jaw spiders.”
Mecysmaucheniidae spiders are especially secretive creatures, tiny and difficult to spot on the forest floor in their native New Zealand and southern South America. Experts have described 25 species in the family, but another 11 await descriptions—and still more are likely waiting to be discovered.
Wood first took note of the trap-jaws more 10 years ago, when she was living in Chile and noticed something unusual: Compared with most other spiders, these spiders’ jaws, called chelicerae, were more elongated and maneuverable, while their frontal region, called the carapace, almost appeared necklike. Curious about why they look the way they do, Wood began collecting them, keeping her finds with her in the field in Chile, and later in her apartment in the United States. For years, she observed her tiny roommates and recorded their behaviors.
The spiders often walked around with their jaws open while hunting, snapping them closed like a mousetrap when they encountered prey. But that elusive moment of attack happened so quickly, Wood couldn't manage to get it on film.
Still, she did not give up. Eventually, she was able to record 14 species of the spiders with a high-speed camera. She was shocked to find that capturing the snapping-shut action of some species’ jaws required filming at 40,000 frames per second (a regular video camera films at about 24 frames per second).
Wood used genetic sequencing to elucidate the evolutionary relationships between 26 species of the spiders. Finally, she used a particle accelerator—essentially, a very strong X-ray beam—to create 3-D computer models of many of the spiders, which allowed her to digitally dissect and measure spiders that were otherwise too small to handle.
In the end, Wood assembled enough specimens to examine all of the major groups within the Mecysmaucheniidae family. She found that the fast-snap trait occurs in about one-third of the species, but, as her phylogenic analysis revealed, it has evolved in four separate instances.
Of the 14 species she was able to get on high-speed video, the fastest could snap their jaws shut in 0.12 milliseconds, which was more than 100 times quicker than the slowest. She also found that the smaller the species, the faster its jaw-snapping capabilities.
The actual mechanism behind the spiders’ lightning speed remains a question for future studies. Although for now, Wood and her colleagues know that it exceeds the known power output of muscles, implying that some other structure must be responsible for releasing all of that stored energy.
Simply finding enough Mecysmaucheniidae spiders to undertake the study was quite an accomplishment—much less pulling off the technical work needed to analyze their anatomy and high-speed behaviors, says Jeffrey Shultz, an arachnologist at the University of Maryland at College Park who was not involved in the work.
“The fruits of all this effort was to show that a peculiar mechanism—which one might have regarded as the product of a unique evolutionary event—has actually appeared four separate times in this group of spiders,” he says. “It will be interesting to find out if the power amplification mechanism is also the same in each evolutionary iteration and, if so, why this particular group of spiders seems to be uniquely predisposed to it.”
That is a question Wood hopes to answer in future studies, although she already has a hunch. The smaller spiders seem to prefer a diet of springtails—very fast insects that rapidly jump to escape predators. It could be that the quickest trap-jaw spiders evolved their lightning-fast attack so that they could target this speedier prey.