Bibionids are distinctive looking flies with striking differences between the sexes. Females have narrow, elongate heads whereas males have far more rounded heads that are largely encompassed by the eyes. This sexual dimorphism can include body colour differences where often the female is reddish and the male black. Some genera have modified foretibial spurs or spine sets allowing the female to dig soil for the purpose of ovipositing. Their larvae are generally thought to feed on decaying vegetation, usually in soil or leaf-litter. Certain European species of Bibio are reported as sporadic pests on the roots of cereal crops but this has not been the case in Australia. Adult Dilophus species are often found feeding at flowers and may be important pollinators.
Tasmania has 7 known species – Plecia dimidiata (Pleciinae), Bibio imitator (Bibioninae), and 5 Dilophus species (Bibioninae). Dilophus have fore tibiae with an apical ring of spines in addition to other sets placed in the middle. Bibio instead posses a large apical spur. Plecia have simple (unmodified) tibiae.
Hardy, D. E. 1982. The Bibionidae (Diptera) of Australia. Australian Journal of Zoology 30: 805-55.
Harrison, R. A. 1990. Bibionidae (Insecta: Diptera). Fauna of New Zealand 20: 1-28.