© Simon PollardMenemerus bivittatus is one of three species of jumping spider that steal food from ant columns.
Forget stealing from the mouths of babes, zoologists have observed a similarly heinous crime - spiders stealing food from the mouths of ants.
At Mbita Point on the shores of Lake Victoria in Kenya, the walls of the buildings and other surfaces are covered with insects, including thousands of tiny lake flies. Within the throng lurks Menemerus
, one of the jumping spiders or saltacids.
These predatory spiders adopt an approach similar to the big cats when hunting. They move very slowly, with their body close to the ground, before leaping on their prey.
Stalking is helped by extremely good vision: there are eight eyes in total, and importantly, two that face forward. These anterio-medial eyes have a visual acuity about one sixth as good as humans and let them "see like a primate and hunt like a lion," says Simon Pollard from the University of Canterbury in Christchurch, New Zealand, who led the study.
Jumping spiders are also are known to be capable of solving cognitively complex tasks.
Now Pollard and colleague Robert Jackson, have filmed three species of Menemerus
adopting an alternative feeding strategy: stealing recently killed lake flies from ants and carrying their loot back to the nest. This is a behaviour not seen since 1936, when it was first documented in India.
The jumping spiders - ranging from 2 to 6 millimetres in length - lurk about 10 centimetres from a column of ants on the wall. After about 5 seconds, the spider scuttles in and uses its mouthparts to snatch the object from the ant's jaws, before returning to its home to feed. This process may be repeated for as many as four times in one feeding session.
Pollard says that the snatching method may offer a less energetic way of ensuring a meal compared with the usual stalking and leaping technique - live prey do sometimes manage to avoid the spiders' attacks.
Stealing might also be a way of getting the ants do the hard work, picking out fresh and nutritious flies from those that have dried up, he says.
will often spend the time and energy stalking and leaping on a dead lake fly," says Pollard. "Like macabre puppets, the corpses of lake flies trapped by a strand of silk [from various species of spider] can dance in the wind just like live flies."
But long dead flies are no use to the spiders as they won't be moist enough to produce the soupy mix of saliva and bodily fluids necessary for digestion. Without ants do the sorting, the spiders might waste energy.Learned behaviour?
Eileen Hebets from the University of Nebraska in Lincoln told New Scientist
: "I think one of the most intriguing aspects is the possibility of learning being involved in this foraging strategy. I would love to know if exposure to another individual foraging in this way increases the likelihood of attempting it on one's own."
Jérôme Casas from the University of Tours in France suggests that it might also be interesting to look at the behaviour of robbed ants. "It might change according to the 'value' of the lost prey," he says.
Journal reference: Journal of Arachnology