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A mid-air cartwheel, the judicious use of sticky silk and a quick rappel down a tree, all in the blink of an eye: researchers have identified how the Australian ant-slayer spider captures prey twice its size.
The acrobatic behaviour of the Australian ant-slayer spider, Euryopis umbilicata, as it hunts and eats banded sugar ants has been documented by scientists for the first time.
During the day, the ant-slayer hides under the bark of Eucalyptus trees. At night, it perches on tree trunks and waits for the approach of unsuspecting ants. The tiny arachnid measures up to 6mm in size and its prey can be around two times larger.
“It has this crazy way of hurtling itself at an ant, doing this fabulous cartwheel then, like Spider-Man, attaching a piece of silk in mid-air to the ant,” said the study’s senior author, Prof Mariella Herberstein of Macquarie University.
“Then it keeps on twirling away from the ant while the ant is being captured. At that stage [the prey’s] fate is sealed.”
All the steps in the spider’s attack sequence occur within less than a second, which Herberstein described as an “unbelievable” feat.
She likened the ant-slayer to a mountaineer rappelling down a rope. “One end of the rope is attached to the tree trunk, the middle part of the rope has a bit of glue that is attached to the ant, and at the end of the rope is the ant-slayer spider.”
After the sugar ant is secured, the spider then runs its silk around the ant.
“When the ant is sufficiently immobilised, she takes a small nibble on the foot of the ant, and the venom does its thing,” Herberstein said.
In an analysis of 60 hunts, the researchers found the ant-slayer was successful in 85% of encounters with its prey. The only times the spider was unsuccessful was when the ant fell off the tree trunk before the ant-slayer was able to tag it with silk.
The ant-slayer belongs to a family of spiders, Theridiidae, which is well adapted to forage on the six-legged insects. Many other species in this family, including the redback spider, also have sticky silk but rely on a web to catch their prey, rather than through the direct contact the ant-slayer prefers, Herberstein said.
The behaviour was first observed by Alfonso Aceves-Aparicio, a PhD student at Macquarie University and Universitat Hamburg. He noticed the tiny spiders sitting on tree trunks, waiting for ants as they travelled up to the crown of the tree, where nectar and insects are plentiful.
The Australian ant-slayer is found in the east of the country, in Queensland, New South Wales and Victoria.
More than 99% of the ant-slayer’s prey was ants, and 90% of its diet was made up of the banded sugar ant specifically – an unusual behaviour among spiders, the researchers noted. “We think of spiders as being predators … but they’re generalists, which means they more or less eat everything,” Herberstein said.
There are some other spiders with specific appetites. Bolas spiders, for example, only eat male moths and mimic the pheromones of female moths to attract their prey.
Of more than 50,000 spider species described globally to date, only one is known to be a vegetarian: Bagheera kiplingi, a Central American jumping spider.
The study was published in the Proceedings of the National Academy of Sciences.
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