Melanostoma dubium (Zetterstedt, 1838)
There is much confusion about this species. Stubbs & Falk (1983) described 'form A', intermediate between M. dubium and M. mellinum, and the work of MacGowan et al. (1997) showed that these form an altitudinal cline and question whether M. dubium is really a separate species. Recent DNA analysis (ref) suggests that the interpretation of MacGowan et al. (1997) was correct. A species that remains on the checklist until voucher material is checked.
Biology & ecology:
The larva is unknown, but assumed to be a general predator amongst leaf litter like others of this genus. Adults are found at higher altitudes on moorland, especially along stream sides and around wet flushes.
Recorded from the main upland areas of Scotland and northern England from around 250m upwards. Perhaps most often found above 500m (although there is little hoverfly recording at this altitude). Although there are old records from the Pennines, Cumbria and Exmoor, there are very few recent English records and only from the higher peaks of the Cumbria.
Status & conservation:
Although there appears to be a strong decline, this may be due to very limited recording effort at high altitude since surveys in the 1980s. If it is genuine, this is a scarce upland species, but perhaps under-recorded because of the difficulty of reliably separating it from M. mellinum.