Snake-flies, alderflies, lacewings and scorpion flies in Essex
Order MEGALOPTERA
Alderflies are familiar and distinctive insects, which are typically associated with the marginal
vegetation of rivers, lakes and ponds. They have no particular association with alder trees (Alnus
spp.) and it is presumed that the association was made because these trees too arc often found in
waterside situations. The greyish egg masses are laid on emergent vegetation or, more rarely, on
inorganic objects at the waterside. The larvae emerge after 7-14 days and crawl to, or fall into, the
water where they are truly aquatic and active predators of a range of water invertebrates. The larval
stage usually lasts for two years in lowland Britain. In the early spring the larva emerges from the
water and excavates a chamber about one centimetre down in waterside debris. After about three
weeks, the mobile pupa climbs adjacent vegetation and the adult emerges. Emergence of adults is
frequently synchronised and it is not unusual to witness many hundreds of newly emerged adults
resting on waterside vegetation.
The name Megaloptera is derived from the Greek megalo, the stem of megas = great, and the Greek
pteron = a wing.
Family SIALIDAE — the alderflies
There are six species in Europe in a single genus, but only three in Britain. Two species are recorded
for Essex, though one is represented by only a single record and is perhaps under-recorded. The third
species is not considered likely to be found in the county.
The three British species can only be separated by examination of the genitalia of the male or the
ventral plates on the terminal abdominal segments of the female, though in both cases the characters
are distinctive. If emergences are encountered, a single voucher specimen should be retained, if
possible, and sent to me for identification.
Sialis lutaria (Linnaeus, 1758)
National status: Common (Common)
Predicted county status: Local/-
Distribution
Existing records pick out the course of the River
Stort, on the border with Hertfordshire, and to a
lesser extent the River Stour in the vicinity of
Sudbury, on the border with Suffolk. In the south-
west corner the ponds of Epping Forest are
evident whilst further cast two records relate to
the River Blackwater. Other scattered records
suggest that the species is very much under-
recorded and there is no reason at all why it
should not be found in the central area of the
county.
Habitat and ecology
The species is recorded from both static and slow-
flowing water, but always where there is a good accumulation of silt, in which the larva hides.
Records from faster waters elsewhere in Britain have proved, upon investigation, to refer to small
backwaters or side channels where the flow is slower and silt accumulates. There arc some British
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