Cistogaster globosa a Bishop's Nightmare

Cistogaster globosa

Last summer I started recording Bishop's Mitre Shieldbugs locally from a variety of grassland sites, with Fordon Banks being the first place I recorded them and perhaps the place in which populations are at their highest and recruitment is greatest. Most insect communities are controlled by a variety of factors including predation and weather, although one of the most significant and often under appreciated is parasitism. Even upon initially finding these populations of shieldbugs I quickly started to search for the host specific parasitic fly Cistogaster globosa. This fly is a member of the large and diverse family of flies belonging to the Tachinidae. 

Today I was searching the grassland at Fordon on what wasn't a particularly good day, with a breeze and dull overcast conditions but was delighted to spot one on a stand of Upright Hedge Parsley, which flowers late in the season and is scattered across the banks. I was sweeping the grassland and spotted the fly quite late, unfortunately catching a brief glimpse and it flew off, frustrated I thought that was it only for it to quickly return to the same flower allowing closer inspection. Checking the umbel heads I found another three males. 

This is still a very rare species in this region, and is scarce in northern England owing to the scarce distribution of its host. Like its host this species will surely become more common as temperatures continue to increase. In Yorkshire there are very few records which occur in isolated areas. Interestingly there was only one record of this fly nationally in the 1950s which shows the scale of its population explosion following its hosts. Interestingly upon checking I found a record of this species in Hunmanby less than 5 miles away from this site from 2019. This strongly suggest that Bishop's Mitre Shieldbug has been established in the wider area for longer than I have been recording them. This is therefore the second local record of the fly.

This is only a small species of fly no larger than 5mm, and exhibits sexual dimorphism with females being all black and males like the one above being a mixture of orange and black. It occurs across a broad range of warm, dry grasslands including arable margins, hedge bases, brownfield sites and sea walls. Hosts in Britain are limited to Bishop's Mitre Shieldbug although other Aelia species are used as hosts in Europe where they occur.