They slipped into southwest France 10 years ago in a pottery shipment from China and have since invaded more than half the country, which is fighting back with drones, poison and even chickens.
The Asian hornet, or Vespa velutina nigrithorax, is considered a "public enemy" in parts of France, where it devours native bees and other insects and, experts say, threatens biodiversity.
"It's exploding [in numbers] and causing trouble," said Eric Darrouzet, a biologist at the Research Institute for the Biology of Insects (IRBI) at the University of Tours.
Pest controller Etienne Roumailhac is exhausted, called to destroy at least six nests a day in the Landes region on the Atlantic coast. Each nest can house thousands of hornets.
"I find them everywhere: garden sheds, mail boxes, car radiators, watering cans," he said.
As the hornet population peaks in mid-summer, business booms. He dislodges nests up to 70cm long, sometimes 20 metres up in a tree.
Roumailhac has tried drones but they get caught in branches, are awkward in urban areas and require official permits that are not easy to get. He relies mainly on a telescopic rod that shoots out insecticide.
Amateur beekeeper Francis Ithurburu swears by another weapon: young chickens that feast on hornets bothering his bees in the town of Biscarrosse. The hornets hover like helicopters by the hives, which gives them an advantage in attacking bees but makes them an easy target for hungry chickens.
Indigenous to Southeast Asia, the hornet, with its distinctive yellow legs and dark thorax, can fan out rapidly. New colonies have cropped up 70 kilometres farther into France each year. Other hornets "hitchhike" to new territory, inadvertently carried by man.
In 2012, France branded the insect a "tropical, invasive species harmful for apiculture", and last year temporarily allowed their destruction with sulphur dioxide, a controversial and restricted chemical linked to respiratory problems.
Yet the hornets have crossed into Spain, Portugal and Italy with a few sightings in Belgium.
In April, Britain put them on a "blacklist", as a parliamentary report warned the "deadly" invader could soon cross the Channel and land on British shores.
Amid the alarm, British papers claimed that six people in France stung by the "killer" hornets died from anaphylactic shock, but the French Anti-Poison Centre contends that they are no more dangerous than other bees or wasps.
So what is the real danger?
"We've spoken mainly about its impact on domestic bees and forgotten to address its impact on biodiversity," said Franck Muller, who researches Asian hornets at the Museum of Natural History in Paris.
The species is highly adaptable and "can survive nearly anywhere," feeding off wasps, flies, beetles and other insects that act as natural pollinators, he said.
In the search for a solution, biologist Darrouzet said the IRBI last year discovered an aggressive little fly larvae "like something out of the film Alien."
Called Conops vesicularis, the parasite is deposited on the hornet queen's belly and once hatched, devours her. Studies are still underway on this and other parasites but Darrouzet is cautious about banking on such "biological warfare".