RSPB Trainee Ecologist Genevieve Dalley tells us about her discovery of a new flying insect species for Scotland. 

A new species for Scotland

In June this year I went to RSPB Insh Marshes in search of freshwater invertebrates. And I wasn’t disappointed! Amongst a wealth of interesting and local species was the star: Molanna angustata, a new species for Scotland.

Molanna angustata

Sometimes the most unassuming little creatures can turn out to be the most interesting. A small, pale brown caddisfly with long antennae; Molanna angustata would normally be one of the first to escape a moth trap unnoticed on a sunny morning.  But a closer look will reveal a sweet little insect with an interesting story.

In Britain there are 2 species of Molanna: Molanna albicans and Molanna angustata. M. albicans is a species largely associated with small lakes. It is found in Ireland, Wales, 2 sites in West Yorkshire then, after a big gap, scattered sites in Central Scotland northwards. M. angustata, on the other hand, is a species of lowland lakes, ditches, ponds and canals. This is fairly widespread across lowland England and Wales, up to the Lake District and Yorkshire. However, it has never before been found in either Ireland or Scotland. The two species have never been found together in the same place.

Molanna albicans distribution

Molanna angustata distibution

In order to identify caddisfly adults to species, the genitals and wing patterns must usually be inspected under a microscope. And it was to my surprise when sorting caddisfly specimens taken from the ‘moth trap’ at Insh Fen that I had two male Molanna, both matching the features of Molanna angustata.

Molanna angustata adult

This was exciting as, looking at the current distribution map, this would only be the second record for Scotland. I sent the specimen to the National Recorder for Caddisflies, Ian Wallace, and it turned out to be even more exciting: the ‘first’ record (Rannoch Moor, 1900) turns out to have been a mistake – a check with the museum revealed the specimen does not exist and was probably a data entrance error. This makes the Molanna angustata I found at Insh the first ever record of this species in Scotland.

Molanna angustata male genitals

This discovery raises more questions than it answers: why has it never before been found in Scotland? Is the species moving north or has it simply gone unnoticed until now? What habitats is the species truly associated with?

There has been a number of examples in the invertebrate world in recent years showing the move of southern species northwards (e.g. Southern Hawker Dragonfly) potentially at the expense of specialist upland species (e.g. Upland Summer Mayfly). Is this the case with the Molanna species? However, this still wouldn’t explain the jump from the current distribution all the way up to Insh. Further investigation is clearly required.

Finding Molanna angustata has reinforced to me the excitement, interest and importance of investigations into understudied species. Whether moth trapping for caddisflies or kick netting in upland streams, you never know what is going to turn up next. There is so much to discover and learn and I couldn’t recommend it highly enough!