Wasps use facial recognition to identify intruders, a new study reveals. These insects usually use smell to recognize intruders and protect their nest.

Liostenogaster flavolineata, a tiny social wasp from Malaysia, was found to identify intruders by the their looks, in addition to their scents. The tiny animals build their home in clusters, with as many as 120 of the shelters in a small area.

Queen Mary University of London (QMUL) researchers, together with investigators from the University of Florence, studied 50 colonies in nature, placing dead and captured wasps close to the natural insect's homes. These lures were implanted with different scents, including those of the local colony, as well as unfriendly insects. They found that wasps in these wild colonies reacted to sight and shape to a greater degree than smell.

Wasps appear to memorize the faces of every member in their nest, and will guard against any insect with an unfamiliar face.

"These wasps can use both face recognition and scent to determine whether another wasp is friend or foe. Unfortunately neither sight nor smell is infallible so they appear to not take any chances and attack anyone whose face they don't recognise," David Baracchi of Queen Mary University of London, said.

Investigators had to travel to South East Asia in order to study these insects. Their nest building, in close quarters, results in many visitors to each nest. These invaders can steal food or other resources, and can lay eggs in nests belonging to other wasps.

Visual and olfactory cues seemed to have different effects on the wasps. When odor was changed, the wasps were more likely to accept outsiders into their nest. When visual features were changed, the animals struck against their own nest mates more often than usual. However, most of these attacks were non-fatal, and did not result in significant injury to either combatant.

Researchers believe that quicker reaction times against wasps with unfamiliar faces could allow the insects to err on the side of caution while protecting their homes. The creatures are able to detect faces at a distance, but the animals need to be in contact with each other to detect scent.

"These findings about individual face recognition in wasps add to a number of recent discoveries about the remarkable behavioural and cognitive sophistication in the tiny-brained social insects," Lars Chittka from QMUL said.

Study of the role of facial recognition versus scent in wasps was profiled in the journal Proceedings of the Royal Society B.