Credit: (left) Pbech/Wikimedia Commons; (inset) Dominik Stodulski/Wikimedia Commons The innocuous-looking harlequin ladybird (Harmonia axyridis, shown left) wields a biological weapon of mass destruction. Europe and North America imported the insects in the early 20th century to control pesky aphids. But the harlequin, native to Asia, began to flourish, crowding out the native seven-spotted ladybug (Coccinella septempunctata, shown inset). Scientists previously thought that the harlequin prospered because of an unusually strong antimicrobial immune system, which would protect it from disease in a foreign environment. But the beetle's more potent secret is a fungal parasite, in the insect-afflicting Nosema genus, which...