Although frequent during the 19th century, this species has all-but-disappeared from most parts of Europe during the 20th century and it should probably be regarded as threatened at European level. Its disappearance co-incided with that of the horse from the European countryside, and it is tempting to speculate that R. rostrata was largely dependent on dry horse dung as a larval microhabitat. But horses are not necessarily a feature of the localities from which R. rostrata is found today (Speight 2010).
Rhingia (Rhingia) rostrata (Linnaeus, 1758).
Linnaeus, C. (1758) Systema naturae... Ed. 10, Vol. 1. 824 pp. L. Salvii, Holmiae [= Stockholm].
Flowers visited by adults: Centaurea, Cirsium spp. (C. eriophorum, C.palustre - D. Levy pers.comm. in Speight 2010), Geranium robertianum, Hypericum, Succisa, and Veronica (Speight 2010).
Flight period: beginning of May to July and from mid ofAugust to beginning of October (Speight 2010).
R. rostrata ranges from southern Finland and Denmark (extinct?) south to northern Spain; from Britain (Wales, southern England) eastwards through central Europe into European parts of Russia, the Caucasus and western Siberia.
Adult flies within woodland, visiting flowers in small glades and dappled sunlight; settles on foliage of large-leaved plants, e.g. Arctium (Kormann, 1993) (Speight 2010).
Preferred environment: forest; deciduous forest (Quercus, Fraxinus/Fagus) and scrub with a rich, tallherbground flora (Speight 2010).
From Speight (2010):
According to Grunin (1939) the eggs of R. rostrata are laid on the underside of the leaves of trees such as Fagus, where there is dung of large mammals on the ground below, the female fly first locating dung in an appropriate condition and then flying up to lay eggs on leaves suspended over the dung. He also notes that eggs can be very frequent on grasses in the immediate vicinity of dung. He observed that females never lay their eggs in dung itself. He says that the larvae hatching from eggs laid on the leaves of trees drop onto the dung, at a stage when the dung is already dry and most of the activity of dung-inhabiting organisms has already ceased. He postulates that R. rostrata larvae require dung “empty” of other dung-using organisms. He suggests that under natural conditions the dung of large ungulates is used and reports once finding larvae in horse dung (noting that horses were then frequent in the forests of the Caucasus), but says that the larvae can be reared on human dung. Evidently the eggs take 5-6 days to hatch, the larvae take approximately two weeks to become fully-grown and they then pupate on the ground. Confusingly, Grunin’s (1939) detailed account of the life history of R. rostrata does not accord with the known habitats of R. rostrata, that are essentially humid forest, normally on a heavy, clay soil. R. rostrata is not a species characteristic of dry forest grazed by livestock and, indeed, is most repeatedly found in forests where ungulate numbers are low – typically confined to wild pig (Sus scrofa) and/or roe deer (Capreolus). It would be very helpful if the life history of this species could be reinvestigated, somewhere where it is still frequent, for example in forests of the foothills of the Pyrenees, to establish whether Grunin’s (1939) observations can be repeated, or whether a rather different picture of R. rostrata’s development emerges.
unless otherwise stated