Bat-Eating Spiders In your Backyard? New Study Says They’re Closer Than You Think [VIDEO]

By iScienceTimes Staff on March 18, 2013 9:47 AM EDT

Bat-eating spider
A small bat gets entangled in a web at the top of the Cockatoo Hill near Cape Tribulation, Queensland, Australia. (Photo: Creative Commons / Carmen Fabro)

Bat-eating spiders sound like one of those super-rare phenomenons that are only found in the deepest, darkest jungles of Nightmareland. But a new study revealed that bat-eating spiders exist on every continent except Antarctica. The bat-eating spider study, titled "Bat Predation by Spiders," reviews more than 50 instances of bats being caught and eaten by spiders by examining everything from academic studies to Flickr accounts.

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"The observation of bat-catching by spiders is not that peculiar if we consider the fact that a number of larger-sized spiders are known to supplement their arthropod diet by occasionally preying on vertebrates," wrote Martin Nyffeler and Mirjam Knornschild in the study.

Although 50 recorded instances of bat-eating spiders sounds like 50 too many for the arachnophobic, the tally comes from more than one hundred years' worth of records. It turns out that while bat-eating spiders are on just about every continent, they don't pose much threat to bats. According to the study, most bats are either too large or fly too fast to become entangled in a large spider web, and those that do are often able to free themselves. Not every bat-eating spider builds webs, however, and the researchers found evidence of hunting spiders, such as the tarantula in the video below, occasionally preying on bats.

"Large-sized Heteropoda spp. are powerful enough to subdue small bats, especially if one takes into consideration that they possess impressive chelicerae, potent venom against small vertebrates, and the ability to move at high speed. Furthermore, these spiders show morphological characteristics suggesting that they may be highly adapted to climb vertical surfaces and walk on cave ceilings. The spiders may climb cave walls and ceilings to catch perching bats or they may search for bat pups fallen from the roost to the floor," said the study.

The majority of bat-eating spiders are web builders, part of the giant orb-weaver genus Nephila. These bat-eating spiders have a 4-to-6-inch leg span and weigh as much as 7 grams. The majority of the bat-eating spiders live in tropical regions near the equator, although there were bat-eating spiders discovered as far north as Ireland. The most common areas where bat-eating spiders are found is Central America and Southeastern Asia.

"In instances seen in Costa Rica and Panama, the spiders had built their webs near buildings inhabited by bat colonies. Bat-catching via spiderwebs was also witnessed particularly often in the parks and forests of the greater Hong Kong area," reported Discovery News.

Researchers also noted that bats may be responsible for a hard-to-explain phenomenon observed in some large orb-weaving spiders: leg loss. According to the study "leg loss in adult female Nephila spiders is a well-known phenomenon. It cannot be ruled out that some of the leg losses occurred during aggressive encounters between spiders and bats trying to defend themselves after being entangled in spider webs."

Ultimately, the study concluded that although bat-eating spiders are more common than previously thought they pose little risk to bats when compared to other predators such as owls and hawks.

"200,000 bats per year are killed as a result of predation by owls and kestrels in Great Britain alone. The fact that bat catching by spiders has been witnessed so infrequently suggests that this type of bat fatality is extremely rare. This is surprising because in tropical/subtropical areas the millions of huge webs of Nephila spp. and Eriophora spp. stretched across the bats' flight paths pose an enormous risk to bats," said the study.

Oh, only millions of spider webs belong to gigantic, bat-eating spiders in the world? That's a relief. Not.

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