The Cornwall Wildlife Trust has now reported two recent sightings of the insects in gardens in south Cornwall, which it believes is a first. The charity speculated that they may have blown over to the county on strong winds or travelled in someone's luggage, rather than escaping from a pet collection.
"It's less likely that they have escaped from multiple people's homes at the same time, and no one has claimed them. They may also have come over in people's luggage or hidden in imports from Europe," said Emma Rosenfeld at the trust.
Dr Luke Tilley of the Royal Entomological Society (RES) said: "Praying mantises are charismatic, unmistakable insects and their appearance in Cornwall is fascinating, a new animal to be spotted in the UK. At the moment these are just sightings, not confirmed breeding populations, but they remind us how insects respond quickly to changes in climate and land use."
Widespread elsewhere in Europe, the European mantis is already well established and breeding in the Channel Islands and the Isle of Wight.
Cornwall is home to an established population of stick insects because the county's climate is so mild and the RES said that the mantises could follow suit. However, that will depend on suitable prey and habitat, the group said.
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The European mantis is an ambush predator that hunts grasshoppers, crickets and other insects. They are known to eat their prey while it is still alive. "Praying mantids are a 'sit and wait' predator, they catch their prey by rapid extension of their fore limbs," Rosenfeld said.
A 2022 study in the European Journal of Entomology found that the species had been spreading northward in Europe due to changes in climate. Milder winters are believed to have helped its shift to higher latitudes.
Tilley urged people to submit sightings of the mantises to websites such as iNaturalist. "The more we understand about new arrivals and shifting distributions, the better prepared we are to protect native species, nature's food chains and our crops," he said.