Bats, says the LiveScience
website, are among the most successful groups of mammals, with more than 1,250 species. Other than humans, they have relatively few natural enemies beyond snakes, hawks, owls, raccoons and possums. But now, the science news site reports, researchers are adding an unexpected predator of bats: spiders.
|A spider feeds on a small bat that is trapped in a web near Cape Tribulation in Australia. Photo courtesy of Carmen Fabro of Cockatoo Hill Retreat, Diwan, Daintree Rainforest, Queensland Australia.
Other invertebrates have been previously reported to dine occasionally on downed bats: giant centipedes in Venezuela, dermestid beetles on the floor of BCI's Bracken Bat Cave in Texas, and whip spiders in Caribbean caves. And, LiveScience
reporter Charles Choi writes, accidental deaths of bats in spider webs have been reported, but were thought to be very rare.
But studies have recently described the killing of small bats by a web-building spider and a tarantula species. This, Choi reports, led researchers Martin Nyffeler of the University of Basel in Switzerland and Mirjam Knörnschild of the University of Ulm in Germany to suggest that bat captures and kills by spiders might be more frequent than previously thought.
They analyzed a century of scientific reports, interviewed bat and spider researchers and examined images and videos. The search, LiveScience
reports, revealed 52 cases of bat-catching spiders around the world. Their results were reported in the journal PLOS ONE.
About 40 percent of known bat-catching spiders live in the neotropics (South America and tropical regions of North America), while nearly a third are in Asia, Choi writes. He says 88 percent of the bat deaths were due to web-building spiders, "with giant tropical orb-weaving spiders with a leg-span of 4 to 6 inches seen catching bats in huge, strong orb-webs up to 5 feet wide."
In Costa Rica and Panama, spiders built their webs near buildings where bats were roosting, while in the Hong Kong area, bat-catching spider webs were most often seen in parks and forests.
Choi says about 12 percent of the reported bat-kills spider reports involved spiders that hunt without webs, such as tarantulas that were seen eating small bats in tropical rainforests of Peru and Ecuador. An attempt by a large fishing spider to kill a bat pup was witnessed below a bridge in the U.S. state of Indiana.
Most bats killed by spiders were either small insect-eating bats or juveniles, and were typically among the common species of the areas. Bats entangled in webs sometimes died of exhaustion, starvation, dehydration or overheating, Choi reports, "but there were many cases where spiders were seen actively attacking, killing and eating these victims."
Bats are probably capable of detecting spider webs with their sonar-like echolocation, LiveScience
says, and only the strongest webs could withstand the impact of a flying bat without breaking. Thus, the website notes, "bat captures are likely rare."
The spiders, nonetheless, are on the hunt.