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Rare Freshwater Invertebrates in Tregaron Bog


There are five species of mayfly and one species of stonefly which were formally found within the Teifi at Tregaron Bog but which have disappeared since they were last recorded in September 1981. All were of localised distribution within Southwest Wales and some are nationally rare. All are associated with slower flowing marginal areas of rivers and with aquatic or emergent plants. Any works on the river which increase the habitat complexity and plant cover are likely to be beneficial to these species but it is almost certain that the species were eliminated by sheep dip pollution in the mid 1990s. Due to their restricted distribution it is perhaps unlikely that all the species would re-colonise naturally, so re-introduction might be considered.


Further details for each species are as follows:-




Labiobaetis atrebatinus (formerly Baetis atrebatinus) – Common name = Dark Olive. This species is associated with the marginal parts of larger rivers and seems to prefer more calcareous waters. It was formally fairly abundant on the Teifi between Tregaron Bog and Pont Gogoyan with records as far downstream as Llechryd. To my knowledge there are no records for this species from elsewhere in Wales. In the River Test SSSI designation this species is described as ‘nationally scarce’ and as ‘very localised’ in the Hampshire Avon SAC citation. It’s scarcity in Wales suggested that it is very unlikely to re-colonise naturally over a reasonable timescale.


Nigrobaetis niger (formerly Baetis niger) – Common name = Southern Iron Blue. It is associated maginal habitats and macrophytes. Apart from the Teifi and a few tributaries, tributaries of the Upper Tywi and a few sites in North-west Wales, it is pretty scarce in Wales. It is listed as a UK BAP species.


Nigrobaetis digitatus (formerly Baetis digitatus). Similar habits to N. niger. Present at low abundance on the Upper Teifi, otherwise unknown from other sites in Wales. Limited distribution also in Southern England and Scotland. Unlikely to recolonise naturally.


Centroptilum luteolum – Common name = Small Spurwing. This species is found in both still waters and slow-flowing rivers. It is very localised on rivers in Wales information from the early 1980s indicating that it is restricted to the Teifi catchment, the Lower Tywi, the Gwendraeth Fach and a handful of sites in North Wales. Formerly widespread in Teifi tributaries but current EA routine monitoring is not to species level so current status unclear.


Procloeon bifidum – Common name = Pale Evening Dun. This species is less widespread than Centroptilum in Wales and in the early 1980s was present only on the Teifi and at one or two other locations. It is more spread in more alkaline waters in England.






Taeniopteryx nebulosa – A stonefly found among the emergent vegetation of rivers, usually in sedge, reeds or grass and sometimes in moss. It is widespread in Great Britain as a whole but there are few records from south of the Tees-Exe line. The British population is an endemic subspecies, Britannica. Date from the early 1980s indicates that it is scarce In Wales being restricted mainly to the main river Teifi, the upper Wye and a few rivers in North Wales. Unlikely to recolonise the Teifi naturally.