Quirks & Quarks

Asian hornets chop off the heads of honeybees

Scientists use tiny tags to seek and destroy hidden nests of invasive predators in the U.K.
View of a dead Asian hornet after it was caught in a hornet nest near Bordeaux, southwestern France, in 2007. Ambushing locals at they return home from work, Asian invaders are dismembering French natives and feeding them to their young. (Bob Edme/Associated Press)

Asian hornet invaders kill off honeybees by decapitating and eviscerating them to feed to larvae. Now scientists are urgently trying to keep a step ahead of the elusive hornets by tracking them with tiny tags.

Honeybee hives in the U.K. and elsewhere in Europe are already in a precarious position because of habitat loss and parasites. Beekeepers started to get alarmed when the first Asian hornets arrived in southwestern France from Asia in 2004 in a shipment of traded goods.

Freed from natural predators, Asian hornet numbers have taken off and they've quickly expanded their range. Beekeepers report a wide ranges of losses, with some moving their apiaries while others saying they've lost 80 per cent of their hive — enough to have to hang up their bee suits.

'We're all on tenterhooks'

Since each nest can produce up to 300 queens, the U.K. government is getting the word out to citizens to report any potential nests. 

"This spring, an Asian hornet queen was spotted by member of public and unfortunately it wasn't contained. There's been no further sighting. We're all on tenterhooks," said Peter Kennedy of the University of Exeter's Environment and Sustainability Institute. 

Asian hornet with a honey bee. (Peter Kennedy)

So why are they so dangerous? The hornets use a "hawking" behaviour to hover 10 to 30 centimeters in front of the beehive entrance, just out of reach of the guard bees who can't mount a successful defence.

Toppling hornets

Now Kennedy, institute director Juliet Osborne and their colleagues aim to keep the invading Asian hornets from colonizing Britain using tiny electronic tags.

The hornets often take a meandering path back to their secluded nests, which makes it a priority for officials to find and destroy the invaders before their numbers swell. 

Kennedy said the hornets don't directly kill the hive. But by not allowing bees to forage then there's no food coming in during late summer or early autumn when honeybees need to build up their reserves for winter. 

In a study published this week in the journal Communications Biology, the researchers describe their success at using radio telemetry. It's commonly used to track birds and mammals fitted with a tag. Kennedy said this is the first time it's been tried on hornets.

Initially when the scientists put the tags on the hornets' backs, it made them too top heavy and Kennedy said they just skidded across the ground.

Then Kennedy hit upon a solution: tie a tiny tag around a frozen hornet so it can't bite the scientist and let the 220-milligram tag hang under the insect like a fanny pack.

A Eureka moment 

Often the hornet was still able to fly back to its nest. Asian hornets could handle about 65 per cent of their body weight, the scientists found.

Kennedy recalled what it was like watch a tagged hornet disappear over the horizon for the first time. "It's like a Eureka moment. We're working on that aim and to see hornet achieve flight is amazing and elating."

On one day, the team was astounded to find one trapped hornet 1.3 kilometers away from the starting point — a reflection of how far the hornets can range and adding to the pressing need to contain spread.

In an email, the Canadian Food Inspection Agency says so far, there hasn't been any sign of Asian hornets in Canada, but federal officials are on the lookout.