The harlequin ladybird was hired to eat aphids and then conquered continents
Farmers released the harlequin ladybird to devour aphids, and it did its job. Then it kept going. Native to eastern Asia, it now thrives across North America, Europe, South America and Africa, poisoning rival ladybirds, crowding into houses every October and occasionally spoiling the taste of wine.
Few beetles come in so many costumes. The common form is orange or red with anywhere from zero to twenty-two black spots, while others are black with two or four red patches, and extreme versions are entirely black or intricately patterned. The beetle measures 5.5 to 8.5 millimetres, large for a ladybird, and a white shield behind the head with dark markings shaped like an M or W is a handy clue. Colour seems largely inherited, but temperatures during the pupal stage may play a part too.
Americans first introduced it in 1916, and for decades it failed to take hold outdoors. Around 1988 a wild population turned up near New Orleans, and within about a dozen years it had become common across the Midwest. Genetic markers studied in 2010 revealed that eastern and western North American populations came from separate introductions, and that the beetles colonising South America, Africa and Europe all descended from the eastern stock, the European ones mixed with a local biocontrol strain.
Its success comes at others' expense. The blood contains harmonine, an antibacterial compound that protects it from disease and poisons native ladybirds that eat its eggs. It also carries a microsporidian parasite that leaves it unharmed yet kills other species. In 2015 it was declared the fastest-invading species in Britain. It also nibbles fruit such as grapes and raspberries, unusual for its family, which helps explain why grapes crushed with beetles can taint wine.
In autumn, harlequins gather on pale buildings and squeeze into walls to spend the cold months, rousing whenever temperatures reach about 10 degrees Celsius. Visual cues and chemical traces left by earlier swarms guide them more than airborne pheromones. Disturbed beetles reflex bleed, oozing a bitter yellow fluid from their legs that smells of dead leaves and stains fabric, and they sometimes give a mild bite. Sealing gaps is the best defence; a vacuum with a nylon stocking tucked into the hose can bag them gently.
Source: Harmonia axyridis
