Since the time of Linnaeus the Neuroptera were often treated as a convenient receptacle for the diverse groups of endopterygote insects that did not fit anywhere else; the modern view is that the group is closely related to the Megaloptera and Raphidioptera . To avoid confusion with the name Neuroptera in its older broad sense, some authors employ the name Planipennia for the modern restricted usage. Even though they are clearly defined as a monophyletic order within the Neuropterida, they still show a wide diversity of size, habits and life cycles, ranging from the tiny Coniopterygidae, or wax flies, which resemble Hemipteran whiteflies; the giant lacewing Osmylus, which has large strongly patterned wings and a semi-aquatic larva; the Sisyridae, or sponge-flies, which have aquatic larvae that feed on freshwater sponges; the large ant-lions which superficially resemble dragonflies, and whose larvae build conical pits in sandy soil to trap prey; and both the brown lacewings (Hemerobiidae) and green lacewings (Chrysopidae) which are familiar visitors to gardens. Neuroptera have predatory larvae, and many adults are also predators on small insects; several groups are regarded as beneficial insects in the garden because of the large numbers of aphids they consume. Lacewings court by 'tremulation', a low frequency sound produced by vibrating their abdomens, which in turn causes the substrate they are standing on to vibrate. The males and females will take turns tremulating; this duet is an essential prerequisite for mating. Worldwide there are around 6,000 known species in 17 families; in Britain there are 70 species in 6 families.