Bat-eating spiders catch bats either in their web or actively attack, kill, and eat bats. Bats that are trapped by bat-eating spiders in webs die of exhaustion, starvation, dehydration, or hypothermia. Since bats are mammals and subject to temperatures, bats and bat-eating spiders are found everywhere on all continents except in Antarctica, reported UPI on March 17, 2013.
“In a new study published March 13, researchers surveyed scientific journals, blogs and even Flickr for accounts of spiders killing and eating bats. They found 52 incidents of spiders munching on bats -- an animal with few other natural enemies -- on every continent except Antarctica.”
The research article “Bat Predation by Spiders” which was published by PLOS, reported that 88 percent of the reported incidences of bat-eating spiders involved web-building spiders. Twelve percent involved hunting spiders.
The six major cases of bat-hunting spiders were observed in Peru, eastern Ecuador, northeastern Brazil, and two cases in India. Tarantulas were observed eating small bats in tropical rainforest areas, eating a bat on the forest floor, or hunting a small bat in a shed. In the United States, a large fishing spider was observed killing a very young bat below a bridge in Indiana.
More unobserved bat-eating spider hunters might be on the kill worldwide since especially young bats are vulnerable to bat-eating spiders. According to a Smithsonian report, females roost apart from males after mating occurred in the fall and winter. Females store the sperm until ovulation time in spring when fertilization takes place. In May or June, bats give birth in large colonies by hanging head up while the young bat is born feet first. The female bat catches the new born and holds it in its pouch. “The baby bat, already large and well developed, crawls to the mother's nipples, attaches itself and feeds.” Initially, while the mother is hunting at night, it might take the very young bat with her. However, once the young stay behind, they cling to the wall or the roof of a structure. Even though bats grow rapidly and can live up to 20 or even 30 years, the young have a high mortality rate. If young bats fall from the roof of a structure, they are not able to climb back up again and can become an easy prey for bat-eating spider hunters.
The large bat-eating spiders which catch bats by using webs have been observed in tropical areas but are found worldwide. The webs of bat-eating spiders can exceed 2 meters (6.6 feet) in diameter or span lengths of more than 20 meters (65.6 feet).
“In the case of Caerostris darwini, an araneid which spins giant orb-webs of up to 2 m diameter across rivers in Madagascar suspended upon bridge lines exceeding 20 meters in length.”
In some instances, bat-eating female spiders build several webs that are connected to each other forming even a larger web area. Other instances of bat-eating spider webs were documented to be in doorways of bat-housing buildings like barns or sheds, or in forest areas. Bat-eating spider webs in forest areas are built at a height of “1 to 6 m above ground.”
Forest-dwelling bat-eating spiders have a leg span of 10 to 15 cm (about 4 to 6 inches) and weigh 1 to 7 grams. Bat hunting was found to be most intense in the time between sundown and midnight when nocturnal bats are most active.
Despite their ability to use echolocation, bats get entangled in the webs of bat-eating spiders when spiders use themselves as “prey” and bats -- thinking they are the “hunter” -- become entangled in the sticky web. Bats might also accidentally become entangled in the web of bat-eating spiders during their flight through thick forest areas or along other limited flight paths.
After having been caught in the web of a bat-eating spider, not all bats die without a fight.
The study published by PLOS reported that some female Nephila spiders were each missing a leg. Leg loss in adult female bat-eating spiders is a well-known phenomenon and is attributed to the “aggressive encounters between spiders and bats trying to defend themselves after being entangled in spider webs.”