Ephemeridae family - ID tips
Class: Insecta; Order: Ephemeroptera; Family: Ephemeridae
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Vital Stats
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Rating
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Scale
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BMWP Score
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10/10
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1 = Filthy to 10 = pristine
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LIFE Flow Group
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2/6
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1= Rapid velocity (>100cm/sec) to 6= drought resistant
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Family level difficulty rating
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2/10
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1= Easy to 10= very difficult
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Species level difficulty rating
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7/10
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1= Easy to 10= very difficult
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There are three species belonging to the Ephemeridae family in the UK. Members of this family are usually the largest specimens of Ephemeroptera (mayflies) encountered in the UK. This family are known as the ‘burrowing mayflies’ as they are capable of burrowing into the substratum, feeding on detritus and filtering particulates. They are easily distinguished from other mayflies by their elongate body form, and large tusk-like projections on the front of the head.
One species, Ephemera lineata, is classified as Red Data Book 2 (vulnerable) and predominantly found in the bottom of large rivers. It is, however, encountered relatively often in rivers throughout the UK whenever deep-water sampling is employed, such as airlift sampling - a fact which leads this author to wonder whether this species is really as rare as previously thought!
The other two species are Ephemera danica, which is relatively common and can be found in many habitats from lakes to fast-flowing streams and rivers; and E. vulgata, which is found less frequently and predominantly in rivers with a muddy bottom (Elliott &Humpesch, 2010).
Identification
The identification of Ephemera species can be problematic for inexperienced taxonomists, particularly as E. vulgata and E. lineata are less frequently encountered than E. danica, due to their habitat preferences, and so can be unfamiliar.
Each species of Ephemera has a series of brown or black marks down the abdominal segments, and these are the primary feature used in their identification. Unfortunately, these marks can become erased in preserved specimens, and annoyingly often in quite large specimens, so when this happens it is very difficult or impossible to identify the species. The following identification features are taken from the Ephemeroptera key, published by the FBA and written by Elliott &Humpesch, 2010.
Ephemera vulgata
The markings on this species consist of triangular marks on every abdominal segment, with the last 4 or 5 segments also having two longitudinal lines towards the centre of the segment, between the triangles (Fig. 1). These lines may be present to a greater or lesser degree.
Figure 1: Ephemera vulgata
Ephemera danica
The markings on E. danica may appear very similar to those of E. vulgata, with the major difference being that the triangles are very weak or absent on the first 4 or 5 abdominal segments. The last few segments also have longitudinal lines between the triangles, as in E. vulgata, but in addition to these, the triangles may have a pale longitudinal stripe through the middle (Fig. 2).
Figure 2: Ephemera danica
Ephemera lineata
E. lineata, like E. vulgata, has markings on each of the abdominal segments, and they take a similar form to those seen in the other two species. However, on the last few abdominal segments, the marks are less triangular and are joined up with the central lines to form marks which look more like a series of stripes than triangles.
Figure 3: Ephemera lineata
There is some overlap in each of these features between the three species, and many specimens are only identifiable by subjective comparison with pictures or other specimens. In addition to these, the FBA key uses the leg shape as an additional feature, describing how the tibial width in E. vulgata is narrower and the margin more angular than the other two species (see Elliott &Humpesch, 2010). Additionally, the width of the femora of each species is mentioned but in practice this is very difficult to judge, particularly in small specimens.
In conclusion, the identification of Ephemera is not always possible, and is more difficult for taxonomists who have never seen each of the species before. Considering that these species are the largest mayflies in the UK, they are surprisingly challenging in their identification, with larger specimens sometimes having less clear markings than smaller specimens.
Get sampling those deeper waters in large rivers, which will now and again yield two or even three species in the same sample – the identification of Ephemera is easier when you are able to compare the markings of preserved specimens side by side!
Ref:Elliott J.M. &Humpesch U.H. (2010) Mayfly Larvae (Ephemoptera) of Britain and Ireland: Keys and a Review of their Ecology. Freshwater Biological Association. Scientific Publication 66
