Wasps give hungry ants the heave-ho

These wasps remove competitors for food, such as ants, by picking them up and carrying them away. Photo / Supplied

In the forests of New Zealand, a war is brewing. Invasive wasps are battling native ants for their food - but deaths are rare.

Instead, wasps pick up their dinner-time competitors and throw them away so they don't have to share food sources, new research shows.

Scientists at Victoria University have identified the "surprising and previously unknown" behaviour after studying the interaction between native brown bush ants and Vespula vulgaris wasps.

Video footage taken in South Island beech forests shows wasps pick up competitors in their mouths, fly off and drop them away from the food.

The experience is the human equivalent of being thrown up to half the length of a football field.

Researchers Phil Lester and Julien Grangier say the ants are not always physically hurt but appear stunned by the experience and often do not return to the food.

Nearly 90 per cent of the removed ants were not injured, even though in some cases the wasps hurled the ants away.

Dr Lester said the discovery was made during a study to see how native species could co-exist with the wasps. He said the wasps "outcompete all sorts of animals for food in these beech forests and drive off anything" - sometimes even native parrots.

"It could be the foraging ants that bring wasps to the food resource. Once there, they adjust their behaviour according to the level of competition imposed by these ants."

But, despite being 200 times smaller, the ants are able to hold their own by spraying the wasps with acid and biting them.

The acid defence may be part of the reason wasps carefully remove the ants rather than kill them.

"When the wasps pick them up and drop them, I would imagine they are getting a mouthful of acid at that time and if they bite too hard they would get an even bigger mouthful of acid - they are really attempting to carry them rather than bite and kill them."

Dr Lester said wasps have nerves in their antennae that pick up pheromones or communication chemicals given out by the ants.

Dr Grangier said the results suggested wasps could assess the degree and type of competition they were facing and adapt their behaviour accordingly. This could also explain why they were so widespread and invasive.

The researchers filmed the wasps around baits of canned tuna. The behaviour was also observed under natural conditions between a wasp and a group of ants foraging in leaf litter for mealworms.

The research is in the British Royal Society's journal, Biology Letters.

additional reporting: NZPA