Mayflies. Ecdyonurus dispar

Transcription

1 Ephemeroptera K. A. Zasada Mayflies Introduction In this account, the term mayfly is used for all Ephemeroptera, and not in the anglers restricted sense for the genus Ephemera alone. There are forty-seven British species of mayfly, belonging to eight families. All have aquatic nymphal stages. Both adult and nymph are of great importance in the diet of fish, and this importance is borne out by the large number of popular names given to them by fly-fisherman, for example, Yellow Upright, Little Claret Spinner and so on. Adult mayflies are easily recognised by their habit of holding their four wings erect when at rest, and by their long slender tail-filaments of which there may be 2 or 3 depending on species. Although the nymphs vary greatly in size, shape, colour and gill form, they are readily distinguished by the fact that all species have three tail-filaments (unless they have been broken off!) and gills on the abdominal segments. Biology and Life History The eggs are laid in water; the time taken for them to hatch varying from species to species, and even within the same species, from a few weeks to several months. The nymphs vary greatly in appearance and mode of life, and show definite adaptation to the type of habitat in which they iive from the rapid water, close-dinging Ecdyonurus to the still water, silt-dwellers like Caenis. Some or all of the first seven abdominal segments carry lateral gills, which differ considerably in form according to genus, some being tufted and others plate-like, etc. At one time it was believed that all these gills had a respiratory function. However, research has shown that the purpose of the plate-like gills of Cloeon is to maintain a flow of water over the surface of the body by rapid vibration, respiration taking place through the thin, chitinous body covering. 35

2 Mayfly nymphs feed mainly on vegetable matter, including filamentous Algae and diatoms, although some are believed to be partly carnivorous. As the nymph grows it moults frequently, the mature nymphs being distinguished by their blackish-brown wing pads. The transformation from mature nymph to mature adult occurs in two stages; metamorphosis taking place at the surface of the water or on a stone or plant out of the water depending on species. The insect hatching from the nymphal skin is not a fully mature adult but an intermediate or sub- with clouded wings and a dull colour - the dun of the angler. This stage lasts from a few minutes to a few hours depending on species before the final moult gives rise to the or spinner. The presence of the sub-imaginal stage in the metamorphosis of mayflies is unique in the insect world. Sexually mature adults usually live for only a few hours, although some females have been known to live for two to three weeks. Their legs are so weak that they are unable to walk, and their degenerate mouth parts do not allow them to feed. Mating occurs in flight, often at considerable height above the ground. The female then lays her eggs in water so continuing the life-cycle. The nymphs, sub-imagines and imagines of mayflies figure highly in the diet of fish. This has led to their shapes and patterns being copied by anglers for use as artificial flies. It has also meant that most of the common species have received popular names. The list below is taken from Kimmins (1972). Angler s names Angler s Curse Caenis spp. August Dun Autumn Dun Black Drake Ephemera danica male Blue Dun (Ronalds) Baetis vernus Blue Winged Olive Dun (B.W.O.) Ephemereila Ígnita Blue Winged Pale Watery Dun Centroptiium pennulatum Brown May Dun Heptagenia fuscogrisea Claret Dun Leptophlebia vespertina Dark Dun Heptagenia lateralis Dark Mackerel (Ronalds) Ephemera vulgata mago Dark Olive Dun Baetis atrebatinus Dun Drake (Ronalds) Ecdyonurus venosus False March Brown Ecdyonurus venosus Great Red Spinner Rhithrogena haarupi, Ecdyonurus venosus, E. torrentis and E. dispar imagines Green Drake Ephemera danica Grey Drake Ephemera danica female Iron Blue Dun Baetis muticus and B. niger subimagines Jenny Spinner Baetis muticus and B. niger male imagines July Dun (Ronalds)?Ephemereila Ígnita July Dun Baetis scambus 36

3 Lake Olive Dun Large Amber Spinner Large Claret Spinner Large Dark Olive Dun Large Dark Oliver Spinner Large Green Dun Large Green Spinner Large Summer Spur-wing Late March Brown Little Amber Spinner Little Claret Spinner Little Pale Blue Dun (Ronalds) Little Sky-Blue Dun Little Yellow May Dun March Brown Mayfly Medium Olive Dun Olive Duns Olive Upright Pale Evening Dun Pale Watery Duns Pond Olive Dun Purple Dun Purple Spinner Red Spinner (Ronalds) Red Spinner Sherry Spinner Small Dark Olive Dun Spent Gnat Summer Mayfly Turkey Brown Whirling Blue Dun (Ronalds) White Midge Yellow Dun (Ronalds) Yellow Evening Dun Yellow Evening Spinner Yellow Hawk Yellow May Dun Yellow Upright Cloeon simile Centroptilum pennulatum Leptophlebia vespertina Baetis rhodani Baetis rhodani Ecdyonurus insignis Ecdyonurus insignis Centroptilum pennulatum Ecdyonurus venosus Centroptilum luteolum Baetis muticus, and B. niger Procloeon pseudorufulum Centroptilum luteolum Heptagenia sulphurea Rhithrogena haarupi Ephemera spp, more particularly danica Baetis vernus Baetis rhodani, B. vernus, B. atrebatinus and B. scam bus Rhithrogena semicolorata Procloeon pseudorufulum Baetis fuscatus, Centroptilum luteolum and Procloeon pseudorufulum Cloeon dipterum Paraleptophlebia cincta Paraleptophlebia cincta Baetis rhodani Ephemerelia ignita Baetis scambus Ephemera danica Siphlonurus spp. Paraleptophlebia submarginata Caenis spp. Ephemerelia notata Ephemerella notata Heptagenia sulphurea Heptagenia sulphurea Rhithrogena semicolorata female female female female imagines subimagines subimagines female floating on the water with wings out-spread after oviposition F 37

4 Mayflies Ameletus inopinatus Baetis muticus Centroptilum luteolum Cloeon dipterum Ecdyonurus

5 Mayflies 2 marginata Paraleptophlebia submarginata Ephemerella ignita Ephemera vulgata 5^ * Ephemera danica Caenis moesta

6 f -z- Ephemeroptera of Sheffield The study of mayflies in this area had fallen off considerably since the work of J. M. Brown in the 1930 s and 1940 s. However, with results from this Survey and data provided by the Yorkshire Water Authority (Y.W.A.), twenty-two species have now been recorded in the District. Since they can be found in both still and running water habitats, mayflies may prove to be useful in water quality estimations. Siphlonurus armatus Etn. Recorded in the Survey from the River Sheaf and two sites at Mark Brook Pond. Nationally few records exist, but it has been found in lakes, ponds and slow streams. Siphlonurus lacustris Etn. Found at four sites, namely Wyming Brook, Blacka Dike, Limb Brook and one still water site, Howden Reservoir. Again, little data exists nationally, but is recorded from lakes, slow streams and high tarns. 3 * Ameletus inopinatus Etn. To date this species has only been recorded locally from running water sites in Derwent Valley. Nationally, it is generally a stream species confined to higher altitudes. There seems no reason why it should not occur in other upland streams in the west of the District. q, Baetis scambus Etn.IB. fuscatus (L.) July Dun, Pale Watery Dun, etc. Found at four sites locally, one in the Rivelin and three in the Sheaf, which fit the national picture of fairly fast rivers. B. fuscatus (L.) is possibly typical of more calcareous waters; the larvae are similar. g Baetis tenax Etn./S. vernus Curt. Blue Dun, Medium Olive Dun, etc. There is no reliable method of distinguishing between the nymphs of these species, but nationally B. tenax appears to be the upland insect. Recorded from Ecclesall Wood (1935) and Wyming Brook (1937) by J. M. Brown, and Abbeydale Hall Garden Pond (1971) by T. H. Riley. (. * Baetis rhodani (Piet.) Large Dark Olive Dun/Spinner The most common mayfly recorded in the District, occurring in all river systems except the uplands in the west. This species seems particularly tolerant of pollution, and is found in the less clean stretches of the Don. "7 * Baetis muticus (L.) Iron Blue Dun, Jenny Spinner, etc. Found at two sites on the River Don. Nationally this species and B. rhodani are typical of rivers and small stony streams. % ' Centroptilum luteolum (Müll.) Little Sky-blue Dun, Pale Watery Dun. Recorded from only two sites; the river Sheaf and Well Springs Pond. Nationally it is common in slow to moderate-flowing rivers and streams and on stony lake shores. l Centroptilum pennulatum Etn. Blue winged Pale Watery Dun, etc. Recorded at only one site on the Moss Brook. Less widespread nationally than C. luteolum. I o Cloéon dlpterum (L.) Pond Olive Dun Recorded locally from eight still water sites. It is common nationally, and can also be found in the slowest parts of rivers. II Rhithrogena semicolorata (Curt,)/R. haarupi (Esb. - Pet.) Yellow Upright, etc. No key exists to separate the nymphs of these two species. Ten records locally, two in Ecclesall Wood by J. M. Brown and the others from the Rivers Sheaf and Rivelin by the Y.W.A. as R. semicolorata. 40

7 / 2 Heptagenia longicauda (Steph.) Only one record at Wyming Brook (1937) by J. M. Brown. Very few national records exist for this species. (y * (Curt.) August Dun, Autumn Dun, Red Spinner, etc. Quite common in the south of the District, mostly in the Sheaf and Rivelin valleys. Although nationally also found on lake shores, all local records are from running water. cj. * Leptophlebia marginata (L.) Quite common locally. Mostly confined to the uplands in the west of the District in both still and running water habitats in keeping with its national distribution. i Leptophlebia vespertina (L.) Claret Dun, Large Claret Spinner Recorded from one site at Canyards Hills Pond. A species generally found in ponds, lakes and slow-flowing water, especially in districts poor in lime. C * Paraleptophlebiasubmarginata (Steph.) Turkey Brown The second most common species recorded locally, occurring in both streams and rivers. Paraleptophlebia cincta (Retz.) Purple Dun/Spinner Recorded from one site only at Canyards Hills. Rather rare nationally. f gr Habrophlebia fusca (Curt.) Found in the Moss and Storrs Dike, at opposite ends of the District! i cj * Ephemerella ignita (Poda) July Dun (?), Sherry Spinner Locally common with a very interesting distribution. Found in the Sheaf Valley, and appears to be spreading into the Don and Porter. <t0 * Ephemera vulgata L. Dark Mackerel (Ronalds) Recorded from three reservoir sites, one at Underbank and two at Moorhall, in contrast to its national distribution where it is common in rivers with a muddy bottom. i t * Ephemera danica Müll. Black Drake, Green Drake, Spent Gnat, etc. Found at two sites on the River Rivelin and one still water site at Tin Mill Pond. Nationally common, occurring in lakes and rivers. * Caenis moesta Bentg. Angler s Curse, White Midge Only one record exists for this species, a relatively recent discovery in Yorkshire, at Abbeydale Pond in the Sheaf valley. References Brown, J. M Dibb, J. R Kimmins, D. E Macan, T.T Some Derbyshire mayflies. Naturalist, The Yorkshire mayflies or Ephemeroptera. Trans. Y.N.U., part 36,1-20. A revised key to the adults of the British species of Ephemeroptera with notes on their ecology. 2nd edition. Sei. Publ. Freshw. Biol. Ass., 15,1-75. A key to the nymphs of British species of Ephemeroptera with notes on their ecology. 3rd edition. Sei. Publ. Freshw. Biol. Ass. 20,