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A colony of Giant Willow Aphids - © Rothamsted Research
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Two weeks ago during a volunteer works party in Beeston
Marsh one of our volunteers discovered a strange black mass covering the stump
of a coppiced willow tree. On closer inspection this mass turned out to be a
colony of insects similar in appearance to aphids yet bigger, in fact much
bigger. They were grey with black spots and had a large distinct thorn on their
back, a bit like a sharks fin. When disturbed the insects waved their long hind
legs around in the air as an act of self-defence. A few photos were taken on
mobile phones as a record, and hopefully to identify them from, and the
conservation work continued.
On return to the Nature Centre the insects were confirmed to
be Giant Willow Aphids - Tuberolachnus
salignus. It would be the first time that this species has been recorded on
the Nature Reserve and it is assumed to be the first time that they have been
recorded in Nottinghamshire too (awaiting confirmation). According to the
National Biodiversity Network's Gateway, which contains distribution maps of most
wildlife species within the UK,
the Giant Willow Aphid has only ever been recorded on two other sites in the
country! However, it is likely that this species’ range has spread and that
under-recording may be responsible for the lack of information regarding its
distribution.
Aphids are probably better known as greenfly and blackfly
and the Giant Willow is one of around 600 species in the UK. Keen gardeners may be all too
familiar with aphids as they will probably spend many hours trying to stop them
from destroying their prized roses and vegetables. Whilst it is true that some species
can cause damage to plants by piercing the soft fresh stems to reach the sap in
which they feed upon, many cause little or no damage at all. That said, at
around 6mm in length (which is big for an aphid) the Giant Willow Aphid looks
altogether rather menacing and is thought to be one of the largest aphid
species in the world (certainly the largest willow feeding species). Although
it is not exactly a garden pest, a great deal of research is being carried out
to see what impact this species could have on commercial willow plantations.
The lifecycle of the Giant Willow Aphid is truly amazing. No
males have ever been found and it is thought that this is because males no
longer exist in this species! The females are able to reproduce asexually without
the need for males. Instead they give birth to live young that are exact copies
of themselves - or clones. So similar are these clones that studies have shown
very little genetic variation between individuals – even between individuals
found on different continents!
Unlike almost every other species of aphid in the UK
adult Giant Willow Aphids and their young can also survive in some of the
harshest of winter conditions often remaining active through periods of snow
and ice. Yet despite extensive studies having been carried out on the Giant
Willow Aphid, there is still one big mystery that remains to be unsolved -
where they disappear to in February. Aphids have been recorded between the
months of August and March, then for almost five months of the year they
completely disappear without trace.
Nottinghamshire is well known for its many different willow
species and The Delta Sanctuary on the Attenborough Nature Reserve (adjacent to
where the Giant Willow Aphid was first discovered) contains one of the largest
continuous expanses of willow woodland in the region - around 25ha. You would
therefore think that the Nature Reserve would provide the perfect habitat for
the Giant Willow Aphid, and that they would be found almost everywhere. However,
on returning to get some more photographs of the aphids they too had vanished
and after many hours of searching, could not be relocated - and have not been
seen since.
Maybe next time you visit the Attenborough Nature Reserve
you could look on the branches and trunk of willow trees on the Reserve and see
if you can find a colony of Giant Willow Aphids for yourself. You may help to
answer the question of where the aphids disappear to for part of the year.
Contact the Nature Centre on 0115 972 1777 or enquiries@attenboroughnaturecentre.co.uk
to report your wildlife sightings.
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