Millions of ladybirds from Asia and North America are set to descend on the UK this winter carrying a fungal infection which could decimate the native population.
The bugs are being spotted in growing numbers across the UK, aided by a mild autumn.
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The Harlequin ladybird was first recorded in the UK in 2004, according to Professor Helen Roy, one of the scientists behind the Harlequin Survey. It can be recognised by its distinctive orange or black wings and is usually larger than its British counterparts.
However, the bugs carry Laboulbeniales, a fungal disease passed on through mating. The infection has only been recorded in a handful of native ladybirds until now and researchers suspect it could have an impact on "the lifespan or the number of eggs a female can produce over her lifespan".
Data recorded over the last decade indicates "seven out of eight native species of ladybird were declining and this was strongly linked to the arrival of the harlequin ladybird", says the survey.
The insects "are very effective aphid predators" and unusually resistant to parasites, it adds, meaning they "easily out-compete" native species.
Although the Harlequin poses no threat to humans besides a small bite, they can emit an unpleasant smell and leave stains on furniture if they get into houses.