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Very
Rare Giant Sawfly found in Radley
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[posted
03/11/2009]
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The
Radley Lakes, that well known local wildlife biodiversity
hotspot, was the location of a recent find of an extremely
rare giant sawfly.
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| Local resident and naturalist Jo Cartmell
found the recently-deceased insect on the ground near
Bullfield Lake on 19th August. At first she thought she
had found a dead hornet, a species known to inhabit the
area. However on closer inspection, she saw it was clearly
something quite different and sought more expert opinion.
However local entomologists were unable to identify it,
and the specimen eventually ended up in the hands of Darren
Mann, Curator of the Oxford Natural History Museum Entomological
Collection, who positively identified it as Cimbex
connatus (Schrank 1776). |
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| This, it turned out, was quite an exciting
find. |
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Photograph: Richard
Lewington
Cimbex
connatus imago
This
is the specimen found in Radley
by Jo Cartmell on 19th August 2009.
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| Up until 1997, Cimbex connatus
was virtually extinct in Britain not having been recorded
for over 90 years, the last record before that being in
1904. In the 19th century, it appears to have been quite
widespread in southern England , having been found in
Suffolk , Kent , Surrey , Sussex , Devon and Cornwall
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| In July 1997, the insect turned up again
near Salisbury in Wiltshire, and since then it has been
recorded with steadily increasing frequency throughout
southern and eastern England , as far north as south-east
Yorkshire . It has now been found in about 20 vice counties,
including several records in Oxfordshire and Buckinghamshire,
as well as Wiltshire. However the 2009 Radley record is
the first for the vice-county of Berkshire (VC 22, in
which Radley is located). |
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| The larvae feed
on alders, including Alnus glutinosa and Alnus
incana . When fully grown, they are about 50mm
long and have a dark dorsal stripe all the way along
the body. They generally feed between July and September,
but may still be found as late as October. |
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| The imago (adult) is large (the Radley
specimen measured 23mm in length and had a wingspan of
50mm) with a superficial resemblance to a hornet, though
without the narrow waist and, of course, the fearsome
sting. |
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There are two
other British Cimbex species, both of which
are also rare. Cimbex femoratus the 'birch
sawfly' has previously been the most frequent. Adults
are black or red-girdled and the larvae are exclusively
associated with birch. The other, Cimbex luteus
remains extremely rare in Britain , although there
have been a few recent records. The adult looks very
much like Cimbex connatus , with which it can
be mistaken, but is has more extensive yellow markings
(which include the first few tergites and underside
of the abdomen). It is associated with willows. |
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Photograph: M.
C. Boddington
Full-grown
larvae of (left to right) Cimbex femoratus
(Yorkshire), Cimbex connatus (Cambridgeshire)
and Cimbex luteus (Cambridgeshire), September
2007.
Scale bar:
10mm.
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| Many of the recent records of Cimbex
connatus seem to be associated with amenity-planted
Italian Alder in such exotic places as supermarket car
parks. It may therefore be the case that at least some
of the modern records are the direct or indirect result
of accidental re-introductions. |
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| Although very rare, neither Cimbex
connatus nor Cimbex luteus has any conservation
status in Britain . Sawflies as a group, are regarded
by horticulturalists as pests because of the damage their
larvae can, and do, inflict on plants. However Cimbex
spp feed on the leaves of specific species of trees,
which are generally able to tolerate the damage, while
the extreme rarity of the genus means that it does not
pose any sort of significant widespread threat. On the
other hand, they are spectacular and impressive insects
as any one may be privileged to encounter in the wild.
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Sawflies
are insects belonging to the suborder Symphyta, one
of only two suborders in the order Hymenoptera (which
is the same order as that to which bees, wasps and
ants belong.) Like other Hymenoptera (but unlike true
flies) the adults have two pairs of membranous wings
(the word hymenoptera literally means ‘membranous
wings') but lack any obvious narrow waist between
thorax and abdomen, a distinguishing characteristic
of Hymenoptera in the other suborder, Apocrita. Sawflies
get their name from the female's saw-like ovipositor,
which is used to cut or drill into the host plant.
The eggs are usually laid in the plant tissue. The
larvae typically resemble lepidoptera caterpillars
and feed on soft plant tissue. The adults generally
feed on pollen and nectar, though some are carnivorous.
There are over 400 species of sawfly in Britain ,
and many are regarded as pests because of the quite
severe damage that large larval populations can inflict
on individual plants.
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The genus Cimbex
belongs to the sawfly family Cimbicidae, which
are also known as ‘club-horned sawflies' because of
their club-shaped antennae. The larval foodplants
of Cimbex spp are trees, willow, alder and
birch being specific to each of the three British
species, C. luteus, C. connatus and C.
femoratus respectively.
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Basil
Crowley
with
acknowledgements to
Jo Cartmell
Richard
Lewington
Darren
Mann
Guy Knight
Mark
Boddington
Bob
Eeles |
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