|[Note Guidelines] Photographer's Note|
|Libellula fulva male/ Scarce Chaser male / Bruine Korenbout mannetje / Spitzenfleck mńnnchen / La libellule fauve mÔle.|
The Scarce Chaser (Libellula fulva) is one of 4 dragonflies found in Britain, in which the mature male possesses pale blue pruinescence on the abdomen". Prior to maturation the male and female look very similar and are highly distinctive with vivid orange colouration, black triangular shaped markings on the upper surface of each abdominal segment and dark bases to the wings. Once mature the males develop a blue pruinescence on most of the abdomen, although the last three segments become black. Adult males can be confused with Black Tailed Skimmers Orthetrum cancellatum and Keeled Skimmers O. coerulescens. However, during mating the female Scarce Chaser clings to the abdomen of the male producing a diagnostic wear pattern on the third segment. This can often be used to help separate these three species.
Ecology and Habitat Requirements:
The Scarce Chaser is a species of lowland river floodplains and is usually found inhabiting slow flowing rivers, water meadow dyke systems and occasionally mature gravel pits(Milne)and nearby ponds. It appears to prefer nutrient rich mesotrophic to eutrophic waters with a pH above 7.0. Inhabited sites characteristically support patches of prolific emergent vegetation, including Common Club Rush (Schoenoplectus lacustris), Reed Sweet Grass (Glyceria maxima), Branched Bur-reed (Sparganium erectum) and Reedmace (Typha). Males have also been observed using silty inlets where Bur reed and Yellow Water-lily were growing along the river margins. Observations suggest that L. fulva sometimes shows a preference for smaller, quieter streams. This type of habitat is not rare in the UK and consequently it is difficult to determine the reasons for the paucity of the Scarce Chaser countrywide.
Dense vegetation appears to be important habitat requirement. It provides niches for the developing larvae within the roots as well as offering shelter and emerging, basking and resting sites for the adults. Semi-aquatic species such as Arrowheads (Sagittaria), Pondweeds (Potamogeton) and Mints (Mentha) also provide suitable breeding and development habitats for prey species. Despite basking on the top of dense vegetation such as tall umbellifers Scarce Chasers do not tolerate exposure and the greatest densities of individuals tend to occur where there is scrub in close proximity to the river. Adjacent woodland is used for maturation, roosting and feeding, particularly in adverse weather, although heavily shaded areas are usually avoided.
Mating appears to be a relatively time consuming and rigorous affair, rarely lasting less than 15 minutes. Once a female has been seized, the pair "flop down at ground level into the vegetation" where copulation takes place. The female then oviposits alone, guarded by the male who hovers close by to ward off intruders. She repeatedly flicks her abdomen onto the surface of the water, choosing slow flowing water, often close to the bank or above the leaves of aquatic plant lying in the water. Females will often stay over the same spot for several minutes and the eggs, which are covered in a gelatinous coat, sink to the bottom and become attached to the substrate. Once hatched the larvae take up to two years to complete their development, living among the silt, mud and semi decomposed detritus on the river bed. They can usually be found where vegetable matter has been trapped in the roots of plants under the bankside in the lee of bends. Synchronised emergence usually begins towards the end of May, although this can be delayed by bad weather. Goodyear found that favoured emergence sites contained a thick growth of Reed Canary-grass (Phalaris arundinacea), with lesser growth of Branched Bur-reed (Sparganium erectum) and Common Reed (Phragmites australis). A variety of other aquatic plants were also present.
Adults can be seen on the wing until early August and observations suggest that males usually fly along the water's edge and not over open water. By comparison females are more frequently found away from the breeding habitat. Observations made by Hinterman indicated that when adults were encountered in surroundings adjacent to the river, they were frequently seen resting in scrub and trees or flying over unmown meadows. L. fulva appears to roost low down in relatively dense vegetation such as Stinging Nettles(Urtica dioica) or patches of tall grass and umbellifers. In these situations it "not only avoids potential predation and disturbance, but is also sheltered from adverse weather conditions".
Only registered TrekNature members may rate photo notes.