Ramson's Hoverfly at Resolven

I've been away the last couple of weeks so apologies for a few belated postings I received via email.
Andrew Lucas wrote:
'A family walk along the canal at Resolven on Easter Monday gave me a chance to do a little hoverfly recording.  One species out in force was Portevinia maculata, colloquially known as the ramson's hoverfly.  Its  larvae burrow into the bulbs of ramsons, and it flies during the plant's flowering period.  Watch out for a fly about the size of a small bluebottle, with distinctive silver markings on the abdomen, buzzing around it's food plant.
Not surprisingly, the species is widely recorded on Gower, but seems to be more local elsewhere in Swansea Neath Port Talbot.  This appears to be the first record for SN80 (according to the hoverfly recording scheme website), but this reflects a lack of recording rather than any great discovery on my part!'