Digitisation on demand: riverflies and redlists | Digital Collections

A guest blog by Robyn Crowther

Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) – or EPT for short – are three orders of insects found in freshwater systems across the world. These three key groups are important bioindicators, meaning that their presence and the size of their populations can give us an idea about the health of a freshwater habitat. There are approximately 89,000 specimens in the Museum’s EPT collection, and the Digital Collections Programme (DCP) are in the process of digitising them. Mobilising this data will aid research being undertaken by the International Union for Conservation of Nature (IUCN), to further our understanding of EPT distribution and assess these species’ vulnerability to extinction.

Why EPT?

EPT are freshwater insects, meaning part of their life cycle occurs in freshwater ecosystems such as rivers, ponds and lakes. Sustaining healthy populations of these insects depends directly on the quality of the water body and the surrounding habitat, and so their presence and the size of their populations can act as an ‘ecological litmus test’ to determine the overall health of a habitat. Reductions in EPT distributions could therefore indicate an erosion of habitat quality. For this reason, EPT are referred to as ‘bioindicators’. Despite the importance of these insect groups for biomonitoring, there are still gaps in knowledge relating to the distribution of species, especially for countries with less rigorous monitoring schemes. EPT museum collections represent an untapped resource that could help to fill these gaps. 

Programmes such as SYNTHESYS+ Virtual Access aim to mobilise museum data by facilitating virtual access to natural history collections for researchers, by enabling holding institutions to digitise a particular part of their collection to meet a specific research need. In the case of EPT, we are digitising the collection along with the Royal Museum for Central Africa and Museum fur Naturkunde to support the research need of the project ‘Data mobilisation for IUCN conservation assessments of global freshwater bioindicators’. Digitising these collections will provide virtual access to the IUCN Species Specialist Group (SSG) for EPT, who want to use the considerable temporal and geographical data held in the collections to ‘red-list’ as many species from these groups as possible. Part of the red-listing process involves assessing how a species’ geographic distribution has changed over time, making the historic data in museum collections describing when and where a specimen was collected a valuable source of information for assessing these species’ vulnerability to extinction.

Capturing the data

The Museum’s EPT collection is vast, containing approximately 89,000 specimens, consisting of pinned, slide-mounted, and spirit material. The current project is focussing on the pinned specimens and slide-mounted material, which equal 65,000 and 9,000 specimens respectively. The DCP has well-established high-throughput workflows for capturing images of both of these types of collections.

For the EPT pinned collection we’re using one of our fastest workflows that utilises the Angled Label Image Capture and Extraction system (known affectionately as ALICE). We’re fortunate that the slide-mounted material in the EPT collection was imaged in 2015, as part of a slide digitisation pilot project that pioneered the use of Inselect – software that automates the cropping of individual images of specimens from whole-drawer scans and similar images generated by digitisation of museum collections. These slide images will be used by the DCP digitisers, along with the newly-generated pinned insect images, to extract, via transcription, important spatial and temporal data associated with each specimen. This data will then be released on the museum’s Data Portal where it can be accessed by the Species Specialist Group for EPT, or indeed by anyone!

We’re currently developing mass digitisation workflows for spirit material, but as these workflows are still in the early stages we won’t be including the spirit collection in this project. However, out of the 15,000 vials that make up the EPT spirit collection a small subset of 2,345 vials were imaged as part of a recent rehousing project so we will be able to transcribe and mobilise some of the data from the spirit collection via the Data Portal, providing virtual access to as much of this collection as possible.

Mayflies, stoneflies and caddisflies

So far, we’ve been talking about EPT as a single entity. For convenience sake, the orders Ephemeroptera, Plecoptera and Trichoptera are regularly combined into the snappy ‘EPT’. This makes sense as they are often found in similar habitats and the issues that affect one order tend to affect all three. Despite this, there are some differences that make it worthwhile to meet the ‘E’, the ‘P’ and the ‘T’ separately…

‘E’ is for Ephemeroptera (mayflies)

The 3,000 species of mayfly that occur throughout the world are probably best known in popular culture for their short life span, and indeed, the order’s name refers to this insect’s short-lived (ephemeral) adult stage. In fact, mayflies can live for years, but most of their life is spent underwater as nymphs. Mayfly nymphs are largely herbivores or detritivores, feeding on algae and plant debris, although some species can be carnivores. This part of their life cycle is by far the longest with nymphs taking up to two years in colder regions to develop, going through as many as 45 moults (when they shed their exoskeleton in order to grow).

Mayflies are unique among insects in that they have an intermediate winged stage between the aquatic nymph and the reproductive adult, referred to as a subimago. This transition stage between underwater nymph and terrestrial adult may only last a few hours or even minutes, depending on the species. Some collectors are either extremely patient or extremely lucky as they have managed to collect specimens at the very moment this emergence happens. Below are two specimens found in the collection that have both the subimago moult and the emerging adult or ‘imago’.

An adult mayfly emerging from  its subimago moult – the specimen is part of the Mosley collection, who preserved his specimens in spirit within small watch glasses.
A pinned example of an adult mayfly emerging from its subimago moult

Adult mayflies do not eat, and their mouth parts are either reduced or completely absent.  This part of their life cycle is devoted to reproduction and is generally very short. The adults are an important part of the diet of many species of fish, including many freshwater game fish, which has led to a whole sport being built around the mayfly. Fly-fishing specialises in catching fish by using mayfly imitations as bait, resulting in many of the common names of mayfly species being given by anglers. We even have some examples of these mayfly imposters in the collection!

A fishing fly vs. a mayfly – from Mosley’s watch glass collection

‘P’ is for Plecoptera (stoneflies)

Stonefiles also have a worldwide distribution, though the majority of the 3,500 species occur in cool and temperate areas. Their aquatic nymphal stage, which usually lasts around a year, prefer fast-moving water where they cling to the rocky bottom. Like mayflies, they are largely herbivorous, feeding on fallen leaves or aquatic vegetation, though some are predatory.

Adult stoneflies live for around two to three weeks, but aren’t often seen as they are reluctant fliers and are largely nocturnal. Some males may even be wingless or have non-functional wings, and they attract a female mate by tapping out a species-specific pattern of beats on the ground with the tip of their abdomens. A receptive female returns the taps and they follow the sound to meet up. Following mating, the female flies to the water and dips her abdomen onto the surface, depositing the eggs. In some species sneaky males have learnt to respond as females, confusing the first male who may end up going in the wrong direction!

Spill the ‘T’ on Trichoptera (caddisflies)

Caddisflies are the most speciose of the EPT group with around 13,000 species. Just like the other two, caddisfly larvae are aquatic and usually live as their aquatic form for around a year, though a few species can be completely terrestrial. Caddisfly larvae are unique among the EPT, as most species build an open-ended cylindrical case that either surrounds their bodies or is attached to the streambed. These cases can be made from a variety of materials including stones, pebbles, leaves and even shells, and some species can be identified from their cases alone. These industrious larvae have even been employed as jewellery makers – the larvae are provided with gemstones and precious metal fragments which they incorporate into their cases. Once the cases aren’t needed by the larvae as a shelter, they are used to adorn the ears, wrists, and necks of people! A few species of caddisfly do not construct a larval case, and these can either be totally free living or can produce silken nets that can trap passing vegetation.

As adults, only some species feed, as like mayflies and stoneflies this life stage is primarily for reproduction. Female adults of some species are flightless, and even those that can fly tend to spend their days resting on bank side vegetation, taking to the wing in the early night. That being said, some species do take part in daytime swarms over streams and ponds. These swarms can include long-horned caddis from the family Leptoceridae, so called for their unfeasibly long antennae!

A caddisfly larva with its larval case – from Mosley’s watch glass collection
An adult long horned caddisfly (Leptoceridae) – from Mosley’s watch glass collection


Due to the current COVID-19 restrictions, our digitisation team has had to pause its on-site activity including imaging the EPT collections. So far we have imaged 20% of the collections and around 30% of the collections are prepped and ready to be put through the ALICE set-up. We have been spending our time working from home transcribing all the records we can get our hands on! This data will be available on the Museum’s Data Portal very soon, and in the meantime,  be sure to check out @IUCN_riverflies and @IUCNssc on Twitter for IUCN news, and keep up to date with other Virtual Access and SYNTHESYS+ projects via @SynthesysEU.

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