Using high-speed videos, researchers have captured trap-jaw spiders striking at their prey. Not only does this occur at lightning speed, it’s also power amplified, according to findings published in Current Biology this week.

Power amplification is when an animal produces high power output by releasing stored energy instantaneously – resulting in movements that exceed the maximum power output of its muscles. Power-amplified trap-jaw mechanisms are found in several types of ants, but these extremely fast predatory strikes haven’t yet been reported in arachnids. 

Rather than capture prey using webs, spiders in the family Mecysmaucheniidae hunt on the ground using their highly maneuverable, jaw-like mouthparts called chelicerae. They stalk their prey while opening the chelicerae, then they snap them shut when they’re close. These spiders are only found in New Zealand and southern South America, and they’re tiny, weighing between just 0.5 and 23.1 milligrams. 

A team led by the Smithsonian Institution’s Hannah Wood used high-speed video cameras to record the cheliceral strikes of 14 species of trap-jaw spiders. The specimens were placed in a glass tube, and the researchers used an eyelash affixed to an insect mounting pin to stimulate the spiders. The team made a total of 98 recordings ranging from 1,000 to 40,000 frames per second.

These spiders snapped their chelicerae shut at extreme speeds, though there was a wide range: The fastest species is two orders of magnitude faster than the slowest one. Furthermore, the power output from four of the species surpassed the power output of their muscles. That means in order to amplify power, the spiders must have evolved innovative structural mechanisms for releasing stored energy to produce ballistic movements. 

The researchers also scanned specimens representing all 26 species in the lineage using X-ray microtomography. Based on their measurements and 3D visualizations, they found several structural innovations related to cheliceral function, including a highly modified carapace (or shell) for orienting cheliceral muscles horizontally and a modified exoskeleton for muscle attachments.

And finally, using molecular data, the team discovered that the high-speed, power-amplified predatory strikes have evolved at least four times independently within this spider family.

^{Image in the text: The female of a new Mecysmauchenius species. H. Wood}