Does a spider need a web to catch its prey?
What sort of spider can capture its prey without a web? We think of spiders as web-makers, but about half of all known spider species do not make webs. Still, they have organs called spinnerets that spin out silk for other uses. Silk can help a spider wrap up their eggs to make an egg case, line its burrow, or swing to the ground from a branch.
All spiders are predators, and they sport a huge variety of tactics for capturing their prey. Spiders that do not make webs have other ways to get their meals. A wolf spider hunts down prey, pounces, and may use its long legs to straight-jacket it. A fishing spider gets its meal by scurrying over water towards vibrations made by prey. A bolas spider dangles sticky balls made of silk and mucus that are scented to lure in moths. A spitting spider launches a sticky fluid to immobilize its victims.
Regardless of their capture technique, nearly all spiders use venom. Once a spider has its prey in hand (actually in its grasping appendages called "chelicerae"), it pierces it with sharp fangs to inject the venom. Spider venom can damage nervous systems or other body tissues, depending on the species. But the vast majority of spider venom does not cause any harm to humans.
One group of spiders with a long name (Palpimanoids) tends to specialize on eating other spiders. What's odd is that the way these spiders capture prey may be as complex as their long scientific name. The pelican spider plucks at other spiders' webs, then swings its super-long chelicerae outward to pierce them after attracting them over. Another spider in the same group has vice-like chelicerae that snap shut on its prey with an acceleration that can exceed 1,000 times the acceleration of a space shuttle. Dubbed the trap-jaw spider by Smithsonian entomologist Dr. Hannah Wood, its jaw-like parts look like they are doing splits while they wait in the open position for prey.
Learn more about how spiders capture prey in a live "Smithsonian Science How" webcast on Thursday, January 12, 2017. In "Powerful Predators: Adaptations of Trap-Jaw Spiders" (airs at 11 a.m. and 2 p.m. EST on the Q?rius website), Smithsonian scientist Hannah Wood will show you the technology she uses to analyze spider predator adaptations and answer your questions live. You can also get teaching resources to use with the webcast.
CRITICAL THINKING QUESTION
How do vibrations help a fishing spider?
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