14
The Essex Naturalist
days they hatch and the young larvae fall into the water below to drift (rarely
swim) until making contact with a sponge. Upon such contact the young larva
immediately inserts its jaws into the sponge and feeds by sucking up host fluids.
When mature, the larvae swim to land and attach themselves to solid objects
such as bridge supports or trees. Midsummer larvae pupate at once; autumn
larvae rest as prepupae and pupate in the spting. Adults always emerge after
sunset and are readily attracted to lights.
The giant lacewing Osmylus fulvicephalus is the only British representative of
the family Osmylidae and is far more common in the west of Britain where the
amphibious larvae are voracious predators amongst the mosses of the splash zone
in fast-flowing and boulder-sttewn streams. This is our largest lacewing. It is
active at dusk but is a poor flier and preys mainly on aphids and adult moths
taken at rest. It is interesting to note that it is the male Osmylus that is passive
in courtship, releasing pheromones to attract a female rather than the other way
around. Spermatophore exchange takes up to a hour, which represents 3% of the
male life-span (equivalent to the act of human reproduction lasting for 18,396
hours!). Eggs are laid in damp moss and hatch after four to 22 days depending on
temperature. The larvae tunnel into the moss and feed initially on mites,
Collembola and other small arthropods but in the second and third instar rely
on Diptera larvae, especially Chironomidae and Tipulidae. The prey is
penetrated with the modified jaws, becomes paralysed by the salivary fluids and
the contents are then sucked out. Paralysis is instant in small prey but can take
up to ten seconds in Chironomid larvae. In the late autumn the larvae burrow
deep into the moss and enter diapause in which state they can survive total
immersion in water. A cocoon is spun in April/May and there follows a pre-
pupal stage lasting from 7-18 days before the pupal stage which lasts 10 to 14
days. When mature, the pupa emerges from the moss and attaches itself to a firm
support before the adult emerges.
There are recent Essex records of the giant lacewing from the Little Baddow
area where adults were seen in the last few years by Geoff Pyman and it would
certainly be worth looking out for these distinctive insects in other areas of the
county. During July and August they can sometimes be found resting in the
shadow underneath the horizontal surfaces of bridges over streams.
Our brown lacewings all fall into the very large family Hemerobiidae. No less
than eighteen species ate recorded for the county, though two of these -
Hemerobius atrifrons and Wesmaelius quadrifasciatus have not been seen for a
number of years and may now be absent. A further twelve species are to be
found elsewhere in Britain and perhaps one or two of these may still yet be
found in Essex. Two or three species are very common and often abundant in
Essex. Beating hedgerow vegetation from May onwards will invariably produce
Hemerobius lutescens and, about a month later, H. humulinus. Tapping the
branches of oak trees in July or August will very likely disturb H. micans