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Wild Things

The weird and wonderful in the natural world

Sarah Zielinski

Wild Things

Wild Things

Delicate spider takes down tough prey by attacking weak spots

Loxosceles gaucho recluse spider

The Loxosceles gaucho recluse spider (left) can kill a heavily armored Mischonyx cuspidatus harvestmen (right) by disabling its weak spots, a new study finds. Here the spider is inflicting a long bite to a joint on the harvestman’s third leg.

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Like a miniature martial artist, the Loxosceles gaucho recluse spider can sneak up on a heavily armored harvestman (a type of arachnid), identify its weak spots and quickly disable its meal, a new study reveals.

This species of recluse spider lives in and around Sao Paolo, Brazil. Often the spiders are found near and inside people’s homes, dwelling under tree trunks, dead palm fronds and bricks. They eat a variety of arthropods, including crickets and Mischonyx cuspidatus harvestmen.

Harvestmen aren’t typical meals for such delicate-bodied spiders because their thick cuticle has only a few spots, such as their joints, that would be vulnerable to a spider’s bite. But after finding dead harvestmen on L. gaucho spiders’ webs, Julio Segovia of the University of Sao Paolo and colleagues suspected that the spiders somehow overcome the harvestmen’s defenses.

The researchers came up with a series of hypotheses about how the spiders might accomplish the feat: The spider tracks down a harvestman via chemical cues. It detects its prey through vibratory cues. And the spider’s web helps it handle the harvestman so that it can bite the arachnid in its vulnerable spots. The researchers tested each of these hypotheses and reported their findings in the March Animal Behaviour.

First, they put hungry spiders into an arena with one spot that had chemical cues from harvestmen and another with chemical cues from crickets. The spiders had no preference for either one. Nor did the spiders prefer either of the cues over that of a blank piece of paper. So scent is probably not leading them to a meal.

The scientists next tested the spiders’ ability to sense vibrations by letting them prey upon harvestmen on paper and on granite. There was no difference in the spiders’ hunting ability — so they’re probably not using vibrations to sense their prey. And in a test of the third hypothesis, the presence of silk had no effect on the spiders’ ability to capture the harvestmen; that hypothesis was wrong as well.

The behavior of the harvestmen during tests was unusual, as well. “Harvestmen have a pair of scent glands used to repel predators,” notes study coauthor Rodrigo Hirata Willemart of the University of Sao Paolo. “It came as a surprise that these harvestmen did not release their smelly secretions against a predator with such a high success in eating harvestmen.”

Videos of the spiders finally revealed their hunting strategy: The spider spots a harvestman and then approaches or brushes by its prey. At that time, the spider is probably identifying weak spots to attack. Then it delivers a series of short and/or long (up to several minutes long) bites until the harvestman stops trying to get away. Finally, the spider weaves silk threads around its meal.

“Sometimes the harvestmen freeze,” Willemart says. “Sometimes they attempt to scurry away. But the spider is faster and quickly manages to move and stay in front of him. The harvestman goes right, the spider goes right, always in front of the prey.”

The recluse spider can disable a cricket faster and with fewer bites, probably because that insect lacks the harvestman’s heavy armor and require less venom to subdue, the scientists note. That may explain why earlier researchers reported finding more crickets than harvestmen in the spiders’ webs — the crickets are the easier meal.


Where an ant goes when it's gotta go

By Sarah Zielinski 12:17pm, February 24, 2015
Scientists found black garden ants defecating in certain spots inside their nests. The researchers say these spots serve as ant toilets.

Five surprising animals that play

By Sarah Zielinski 2:33pm, February 20, 2015
No one is shocked to find playful behavior in a cat, dog or other mammal. But scientists have documented play in plenty of other species, including reptiles and insects.

Cliff swallow breeding thwarted by bird version of bedbugs

By Sarah Zielinski 12:15pm, February 18, 2015
A 30-year study of cliff swallows in Nebraska finds that the birds will abandon nests, rather than have a second brood, when their homes are infested with swallow bugs.

Fertile hermit crabs turn shy

By Sarah Zielinski 11:00am, February 13, 2015
Male hermit crabs that aren’t carrying much sperm are bolder than their more fertile brethren, a new study finds.
Animals,, Ecology,, Conservation

Cats and foxes are driving Australia’s mammals extinct

By Sarah Zielinski 11:56am, February 11, 2015
Since the arrival of Europeans in Australia, a startling number of mammal species have disappeared. A new study puts much of the blame on introduced cats and foxes.
Animals,, Biophysics,, Evolution

Toads prefer to bound, not hop

By Sarah Zielinski 2:30pm, February 6, 2015
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Huge, hollow baobab trees are actually multiple fused stems

By Sarah Zielinski 11:54am, February 4, 2015
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Climate,, Animals,, Oceans

Warming Arctic will let Atlantic and Pacific fish mix

By Sarah Zielinski 12:00pm, February 2, 2015
The ultra-cold, ice-covered Arctic Ocean has kept fish species from the Atlantic and Pacific separate for more than a million years — but global warming is changing that.

Ant-eating bears help plants

By Sarah Zielinski 5:44pm, January 27, 2015
A complex web of interactions gives a boost to rabbitbrush plants when black bears consume ants.

If pursued by a goshawk, make a sharp turn

By Sarah Zielinski 7:00am, January 22, 2015
Scientists put a tiny camera on a northern goshawk and watched it hunt. The bird used several strategies to catch prey, failing only when its targets made a sharp turn.
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