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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.

Climate,, Oceans,, Ecology

Resilience protects corals from hurricanes — and climate change

By Sarah Zielinski 4:54pm, December 5, 2014
Coral reefs have evolved to be resilient in the face of hurricanes that can devastate human populations. But climate change is reducing the ability of reefs to bounce back from disaster.

Platypuses are full of mystery

By Sarah Zielinski 10:05am, December 3, 2014
With duck bills, webbed feet and venomous spikes, platypuses are one of the weirdest animals you’ll ever be lucky enough to see.

Ten bites of turkey trivia for your holiday meal

By Sarah Zielinski 7:16am, November 26, 2014
Will turkeys really drown if they look up in a rainstorm? Can they fly? Where did the domestic turkey come from? Learn answers to these questions and more.
Animals,, Ecology,, Oceans

Scientists’ tags on fish may be leading seals to lunch

By Sarah Zielinski 5:53pm, November 20, 2014
In an experiment, 10 young grey seals learned to associate the sound of a pinging tag with fish. The tags may make fish vulnerable to predators, scientists say.
Conservation,, Animals,, Oceans

Tasty animals end up on latest list of threatened species

By Sarah Zielinski 1:59pm, November 18, 2014
Growing food market lands several species, including Pacific bluefin tuna and Chinese pufferfish, on the IUCN Red List of Threatened Species.

Ant colonies prefer homes infected with fungus

By Sarah Zielinski 9:00am, November 14, 2014
Choosing a new nest site ridden with a potentially deadly fungus may be a way for pharaoh ants to immunize themselves against the pathogen, scientists say.
Animals,, Archaeology

Few humans were needed to wipe out New Zealand’s moa

By Sarah Zielinski 10:34am, November 13, 2014
A new study finds that the Maori population was still small when it managed to drive several species of large, flightless birds extinct.

Just enough fat is good for an elephant seal

By Sarah Zielinski 7:30am, November 7, 2014
Fat affects the buoyancy of marine mammals. As elephant seals get fatter, they can spend less energy swimming and more time foraging, a new study finds.
Animals,, Conservation

Dog disease threatens Siberian tigers

By Sarah Zielinski 7:30am, November 4, 2014
Canine distemper virus poses a particular danger to small groups of the big cats.
Animals,, Microbes

Ten real-life Halloween horrors in the natural world

By Sarah Zielinski 10:13am, October 31, 2014
Vampires and witches are nothing compared to mind-controlling parasites, nose ticks and antibiotic-resistant superbugs.
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