Fen Management Handbook - Scottish Natural Heritage

Appendix VIII – Fen management for invertebrates
In general, favourable management of fens should deliver favourable conditions for fen bryophytes,
The major invertebrate groups containing species of conservation significance which inhabit fens, in
approximate order of importance, are:
Diptera (flies)
This is arguably the most important invertebrate group in fens, with a very large number of species
in many families. A wide range of species develop as larvae in saturated peat, mud, or plant litter;
others are phytophagous, or parasitic or predatory on wetland invertebrates. The range of families
and life-histories is very large, as is the range of habitat requirements. The most important areas
tend to be shallowly flooded, seasonally flooded or permanently damp ground with vegetation
cover ranging from bare ground though open-structured vegetation and tussocks to continuous
tall wetland vegetation, but without a deep build-up of litter. Key families include soldier-flies
(Stratiomyidae), crane-flies (Limoniidae, Tipulidae, Cylindrotomidae, Pediciidae), snail-killing flies
(Sciomyzidae), long-footed flies (Dolichopodidae), grass-flies (Chloropidae), shore-flies (Ephydridae)
and hoverflies (Syrphidae) as well as a number of minor families and small numbers of species
from other large families with weaker wetland associations. Where there are associated seepages
there may be a different, and potentially important, assemblage. Craneflies and other Diptera often
dominate in areas of shaded fen. Where trees and shrubs support a significant amount of dead
wood, there may be saproxylic species from several families.
Coleoptera (beetles)
Fens are particularly well-known for their water beetles (in the widest sense, including not only the
traditional water beetle families (Dryopidae, Dytiscidae, Helophoridae, Hydraenidae, Hydrochidae,
Hydrophilidae, Noteridae, Pelobiidae) but also a number of leaf beetles (Chrysomelidae), weevils
(Curculionidae, Erirrhinidae) and marsh beetles (Scirtidae) which have aquatic larvae. Amongst
terrestrial wetland groups, rove beetles (Staphylinidae) and ground beetles (Carabidae) are amongst
the most important. These predominantly ground-dwelling and near–ground-dwelling groups occupy
a wide range of habitat structures, but areas of bare wet ground are important for a number of rare
ground beetles, and conditions varying from this to continuous tall cover with litter account for much
of the habitat range of Staphylinidae. There is also interest in a wide range of other families, including
a wide range of phytophagous leaf beetles and weevils, and members of many other families. Dead
wood and wood-decaying fungi on fens can support substantial assemblages of saproxylic beetles.
Good assemblages of such beetles are most likely to be found where there is long continuity of
mature timber and dead wood, and trees growing in relatively open conditions: such factors may
often be met where there is long tradition of pollard willows, for example.
Lepidoptera (moths and butterflies)
This is a species-rich group in fens, where a very wide range of woody and herbaceous plants
are utilised as food plants. Many of the scarcest species are associated with tall herbaceous
vegetation or beds of reed or other tall monocotyledons: for example, various species of wainscot
moth (Noctuidae) feeding on reed and other tall monocotyledons. South-eastern fens, in particular,
are well-known for the swallowtail butterfly (Papilio machaon britannicus) feeding on Cambridge
milk-parsley Peucedanum palustre, the marsh carpet Perizoma sagittata on meadow-rue Thalictrum
flavum, and the dentated pug Anticollix sparsata on yellow loosestrife Lysimachia vulgaris. However,
others, such as the marsh pug Eupithecia pygmaeata and silver barred Deltote bankiana, are
associated with shorter swards.
Woody vegetation of all types and sizes has value: small chocolate-tip Clostera pigra, for example,
feeds on creeping willow Salix repens, other low willow growth, and small regenerating or invasive
aspen Populus tremula; the large range of species associated with larger trees and shrubs includes
such wood-boring specialists like goat moth Cossus cossus and red-belted clearwing Synanthedon
myopaeformis. A specialised group of footman moths is associated with damp scrub and scrubinvaded
unmanaged reed-beds: the four-dotted footman Cybosia mesomella, the dotted footman
Pelosia muscerda and the small dotted footman Pelosia obtusa.
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