In the family of arachnids, harvestmen have always played Jan Brady to spiders' Marcia, with their charismatic array of predatory talents and perfectly straight blonde hair (kidding about that second part). No longer! Scientists have discovered that harvestmen have a hidden hunting skill: catching prey using glue-coated forelimbs.

"The gluey hairs are widespread among harvestmen," said entomologist Jonas Wolff of the University of Kiel in Germany, co-author of the new study, published Oct. 1 in the Journal of Experimental Biology. "For a long time it was not known what they were used for, or even if harvestmen were successful hunters." While some had speculated that the glue-covered hairs gave the little arachnids information about their environment, Wolff and his co-authors used high speed cameras to show that the glue was in fact used for capturing prey.

The top image shows the glue coated peripalps in action, binding a springtail for consumption. Clockwise, below show (B) how springtail scales can break off in the glue, (E) the glue on the tip of the hair, and (C,D,F) the structure that channels the dollop of glue to the hair tip and keeps it from detaching. Jonas O. Wolff, Functional Morphology and Biomechanics, University of Kiel

Like all arachnids, harvestmen have a pair of forelimbs called pedipalps that they use like tiny, terrifying hands to maneuver food toward their mouths (in scorpions, which are so Peter in the Brady Bunch analogy, pedipalps have evolved into claws). The last two segments of harvestmen's pedipalps are covered in tiny hairlike structures. Each hair is shaped like a drumstick, with a bulbous tip that secretes a gluey fluid.

Harvestmen (also known by their swanky nickname "daddy longlegs") spend their lives creeping around on the soil, hunting the critters that break down dead organic matter. Some of their most-sought prey are insect-like arthropods called springtails, so named for a biomechanical spring on their abdomen they use to propel themselves out of harm's way.

The researchers collected harvestmen from the countryside surrounding their lab, then starved them for a day before putting them in tanks full of springtails. Caught on high speed cameras, the harvestmen used their glue-coated peripalps to ensnare springtails up to twice their size.

But gluing up springtails isn't easy. Not only are their carapaces engineered to repel moisture (glue needs to set before it can stick), they are covered in tiny, detachable scales. However, the harvestman's glue seems to do a good job of overcoming these counter-adaptations. The high-speed cameras showed that within 1 millisecond of contact, the glue had spread into the springtails' complex microstructures. And as the springtail struggled against it, the glue just got stuck to more places. The glue even held against the springtails' trademark leap.

As you can see in the videos below, springtails can put up quite a struggle. The glue is a remarkable adaptation for keeping them from squirming loose. In the first video, even the springtail's trademark snap isn't enough to free it from the harvestman's glue.

This time, the springtail's snap lands right it in the harvestman's arms.

Finally, because you've earned it, here's a video of a harvestman getting his grub on.

Homepage image: Axel Schönhofer