Spider’s Jump Stabilized By Silken Line

Human jumpers are pretty pathetic when compared to jumping spiders. These arachnids can hurdle themselves to destinations of various heights and cover distances up to 25 times their own body length. That’s like a six-foot-tall man jumping 150 feet, starting from a standstill.

Most jumping spiders attach a silk dragline to their starting point, which was thought to be a safety line. That line has a second purpose, researchers have just found — stabilization. They report their findings in the Journal of the Royal Society Interface.

The team of researchers from Taiwan captured 27 Adanson’s house jumpers (Hasarius adansoni) near Taichung City. Twenty-two of the spiders deployed silk when they jumped, and five did not. The five that didn’t use silk ended up being natural controls in a jumping test, letting the researchers compare jumps with and without silk. The scientists had each of the spiders leap three times, filming them with hi-speed cameras (see video above for an example of a jump).

Spiders that used a dragline had a stable body position in the air and a smooth landing. Those that didn’t, however, pitched rearward in the air and landed more upright, falling forward and slipping or tumbling as they made contact with the ground.

“These results suggest that dragline silk can function as a body stabilizer to prepare salticids [jumping spiders] for a predictable, optimal landing posture,” the researchers write, “and hence is critical for these agile and efficient hunters.”

Video from Kai-Chung Chi et al.

Maybe Your Pet Fish Wasn’t Suicidal

guppyWhen I was growing up, my brother had a black goldfish that I swear was suicidal — it kept jumping out of its bowl. If someone saw it happen, they’d just scoop the fish off the floor and toss him back into the water. But of course, the day came when the fish made a leap when no one was watching, and it didn’t survive.

Several of my friends have similar stories. And so does Daphne Soares, a biology professor at the University of Maryland College Park. She was studying the brains of Poecilia reticulata, a species of guppy, when one of her research subjects in the lab jumped out of its tank and into her cup of chai.

“Fortunately it was iced chai and it had a lid on, so he stayed alive,” Soares said in a statement.

Soon Soares and colleague Hilary S. Bierman were recording jumping guppies with a hi-speed camera to find out what was going on. Their study appears in PLOS ONE.

As with the fish that jumped into the chai, the guppies didn’t need any prompting to make a leap out of the water. They didn’t have to be chasing after food, racing to escape a predator, or swimming upstream to migrate like a salmon in order to jump. And unlike other fish that are known jumpers, P. reticulata prepared for their leap by swimming slowly backwards. Then they would start their jumping cycle with fast body thrusts that propelled them out of the water at speeds of more than four feet per second, allowing them to leap distances up to eight times their body length.

Aquarium owners may be familiar with P. reticulata because these fish are one of the most popular species sold as pets. Soares and Bierman, though, studied guppies taken directly from their native habitat in the Guanapo River in the mountains of Trinidad. And the researchers suspect that it’s this habitat that may be key for understanding why guppies jump.

In the mountainous region where the guppies live, the fish might encounter small waterfalls or other barriers as they try to move into new territory. Soares and Bierman hypothesize that the guppies evolved the ability to jump spontaneously as a method to aid this dispersal, which would help them to avoid competition with kin, prevent interbreeding, escape predators, or find new sources of food.

So perhaps my brother’s fish wasn’t suicidal after it — maybe it just didn’t like the bowl it lived in and was seeking a new home.

Image courtesy of flickr user Wolfgang_44

Why The Leafhopper Doesn’t Break Its Leg On Takeoff


With a name like the green leafhopper, you know that Cicadella viridis is probably going to be a keen jumper. These insects can hop with an acceleration of 152 meters per second squared — many times the acceleration of gravity, allowing a successful takeoff — and an average velocity of 0.88 meters per second. That’s only about 2 miles per hour, but it’s not a bad speed for a creature that’s just a fraction of an inch in size.

Roboticists like to study animals such as these to get ideas on how to create better robots, taking shortcuts by harnessing the “design” power of millions of years of evolution. And so researchers led by the BioRobotics Institute in Pontedera, Italy, turned to the green leafhopper to understand how the insect can jump so fast without breaking a leg or destroying the leaf from which it takes flight. Their study appears in the Journal of Experimental Biology.

The scientists collected 67 leafhoppers, a European native, from cane thickets near Pontedera. Then they filmed the insects jumping in the lab, capturing them on film at a rate of 8,000 frames per second to catch the movements in detail.

The powerful jumps are powered by muscles, but muscle-power alone doesn’t explain what’s going on. The leafhopper’s acceleration is nearly constant, which requires that the insect’s leg exert a constant force against the substrate from which it’s taking off. Muscles can’t provide that constant force, and they work too slow for a takeoff that lasts just a few milliseconds. The muscular force also reaches a high enough level that, on its own, it should break the insect’s delicate leg or punch through a thin surface like a leaf.

To translate that strong variable force from its muscles, the researchers found, the leafhopper moves its legs in such a way that the force becomes constant and the stress on both the insect and its substrate never reaches a point where it becomes damaging. That allows a successful takeoff, letting the insect avoid becoming a meal for something bigger.

Image courtesy of Hectonichus on Wikimedia Commons