Fen Management Handbook - Scottish Natural Heritage

Araneae (spiders)
Fens are a very important spider habitat, though most of the scarcer species are found in a wider
range of wetlands. Almost 14% of Red Data Book spiders are associated to a greater or lesser
extent with fens. The rarer species are all associated with open conditions with little or no scrub. The
rarer species are generally associated with vegetated wetland, from relatively open wet grassland to
tall fen and seasonal swamp with a well-developed litter layer. Several species which are relatively
easily captured and identified have been identified as useful key species for monitoring site value and
management success.
Hymenoptera (bees, wasps, ants, sawflies, parasitic wasps)
There is a wide range of sawfly larvae that feed on a range of herbaceous and woody plants,
including some rare species restricted to fens, or to wetlands including fens. Bees and wasps are
not especially diverse in wetlands, but include a number of rare wetland specialists associated
in varying degrees with fens: the bee Macropis europea requires flowers of yellow loosestrife
Lysimachia vulgaris for foraging; the wasps Rhopalum gracile and Passaloecus clypealis, and the
bee Hylaeus pectoralis nest in stems or galls of common reed Phragmites australis; the spiderhunting
wasp Anoplius caviventris lives in structurally complex vegetation at wetland fringes; and
various species require wetland for foraging, or as a source of nesting material.
A wide range of other solitary bees and wasps which nest in dead wood or in dead stems of woody
or herbaceous plants may thrive in fens which contain suitable nesting sites in warm, sheltered
conditions, and significant assemblages may develop in sites which have a wide structural range
and a good set of successional stages. The parasitic families of Hymenoptera are for the most part
rather poorly known, and have been given slight attention in site assessment and management for
conservation. The number of species is high, however, and the specificity of many species makes it
certain that fens are an important habitat for the group.
Hemiptera (bugs)
Members of most British families of Hemiptera may be found in fens. The most important groups
and assemblages, in terms of representation of scarce species, are leafhoppers (Cicadellidae)
and planthoppers (Delphacidae) associated with moderate to tall monocotyledons, especially
where these grow in moderately dense stands or tussocks. There are scarce species also amongst
groundbugs (Lygaeidae), plant bugs (Miridae), especially amongst tall herbaceous vegetation. There
are few species of great rarity, but the lesser water-measurer Hydrometra gracilenta, and the pigmy
water-cricket Microvelia buenoi, species of water margins and shallows, are worthy of particular
note.
Odonata (dragonflies)
The richest assemblages of dragonflies tend to be found in places with a wide range of sizes and
characters of permanent and near-permanent waterbody, especially if there is running water nearby.
They are thus liable to be found in wetland complexes, of which true fen may form a part. Rich
assemblages, however, are not necessarily rich in scarce species. A number of particularly rare
dragonflies are associated with fens, or in water-bodies associated with fens or in fenland districts.
The variable damselfly Coenagrion pulchellum may be a component of ditch systems and ponds in
fens; like the Norfolk hawker Aeshna isosceles, it also occurs in grazing marsh ditches. The scarce
chaser Libellula fulva is found in fenland areas, and sometimes found as an adult in large numbers in
fens, but breeds in rivers and large drains.
Other rare species have a rather broader ecological range. The small red damselfly Ceriagrion
tenellum can occur in shallow, well-vegetated water in fens, but rarely: it is more usually a wet heath
and bog species. The Irish damselfly Coenagrion lunulatum breeds in well-vegetated shallows of
mesotrophic lakes and pools in valley bogs as well as pools in valley fen; The southern damselfly
Coenagrion mercuriale breeds mostly in shallow, base-rich, slow-flowing streams runnels in
heathland, and in chalk streams on river flood-plains. The scarce emerald Lestes dryas breeds in
well-vegetated, often seasonal, ponds and ditches.
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