The larvae of certain flies belonging to the family Syrphidae have long been recognised as plant pests. Merodon equestris, Fab., was recorded in Great Britain as far back as 1869, having probably been imported in narcissus bulbs from Holland (Verrall). This fly is now universally known as the “ Large Narcissus Fly,” the larvae causing serious losses in nearly every locality where the narcissus is grown commercially. More recently flies of the genus Eumerus have been associated with a type of injury very similar to that caused by the larger fly, and the larvae have been recorded on a variety of host-plants in Europe and America. Chief among these hosts may be included narcissus, onion, hyacinth, parsnip, iris, and potato. The flies are commonly referred to as “ Lesser Bulb Flies ” or alternatively in some parts of North America, where they were first recorded as European introductions in 1904, as “ Lunate Onion Flies.”