Here at MGET we are determined to highlight the importance of the Mersey estuary as a biodiversity hotspot and we are interested in all species big or small, dry or wet. To date we have undertaken bird surveys every month of the year for over 5 years, recorded over 7,000 individual fish and conducted day and nocturnal time surveys for aquatic and terrestrial invertebrates (we don’t ignore plants and mammals, but that’s for next time).

The second species from our ‘highlights of 2023’ is one that was detected during a terrestrial invertebrate survey during the summer and is a species that has never been recorded in Cheshire before. In fact, there is so little known about this species its full lifecycle is still unknown, it is…

the Saltmarsh Spotwing (Melieria picta)!

Saltmarsh Spotwing: In 2023 ecologists undertaking invertebrate surveys near Runcorn recorded the first ever Saltmarsh spotwing (Melieria picta) in Cheshire. Photograph taken by Olivier Benoist (Photo 211469381) and obtained under license from iNaturalist.

The saltmarsh spotwing is part of the Picture-winged, or Wing-waving fly family, with around 20 species being present in the UK. Now, I appreciate there aren’t many people who enjoy flies, and for many people they may be seen as nothing more than an annoyance, unworthy of discussion. But the role they play in maintaining a healthy ecosystem cannot be ignored and some species act as very useful indicators that can tell us how healthy (or unhealthy) a habitat is.

Whilst very little is known about the saltmarsh spotwing, we do know that the species is heavily reliant on un-grazed saltmarsh and the distribution of the species in the UK is shifting north. We did however, after a lot of digging through the literature, uncover some super interesting information that provides an intriguing hint about it’s life history.

Observations published by the Dutch Etymologist Juhn T. Smit in 2010[1] indicate that the species is likely a parasite of couch grass (Elytrigia atherica), a common and very rigorous plant species of which we have A LOT of in the upper Mersey Estuary. It seems that Saltmarsh spotwings likely lay their eggs inside the stems of couch grass which helps to protect the eggs and larvae! Saltmarsh spotwings are found in very large number on unmanaged saltmarshes and in areas where grazing is present, this species is found in lower numbers, presumably because there are fewer grass stems into which they can place their eggs.

Whilst further evidence is needed to support this observation, the potential connection between the spotfly and the couch grass is another brilliant example of how important it is that we fully understand the relationships between species and how management of one could lead to the unintentional decline in another.

A huge thank you to Jeff Clarke from Answer Ecology for highlighting this record for us. I wonder what new species 2024 will being!

In other news, we are currently busy planning our public events calendar for 2024 and we aim to provide a number of opportunities for anyone to come and learn more about the wildlife that can be found in and around the estuary. If you are interested please keep an eye out on our social media platform and website for further updates.


[1] Smit, J.T., 2010. De prachtvlieg Melieria picta in grote aantallen op strandkweek Elytrigia atherica op Schiermonnikoog (Diptera: Ulidiidae). Nederlandse Faunistische Mededelingen, 33, pp.1-8.