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The great grey or leopard slug |
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Friday, 06 July 2007 |
In the rainy gloom of this early summer the
large white slug gliding across the woodland
floor could not go unnoticed. It would
seem to be an unusual form of the usually
dark grey leopard slug, characteristically
mottled with darker blotches. Specimens can
reach 30cm (a foot). This one was about 12cm.
Its food is generally rotting wood and leaves
and toadstools.
Leopard slugs have notorious mating habits.
If you have seen David Attenborough’s TV
programme ‘Life in the Undergrowth’, or the
description and illustration in his book of the
same name, you cannot forget them. Two slugs
crawl, one following the other, in the wet
weather, along a high branch in the trees. Since
both are in the same body male and female
(hermaphrodite) who is following whom would
seem irrelevant. Then one forms a mass of thick
heavy slime and deliberately bungee jumps
some 30cm down from the branch, held by a
rope of this mucus. The other follows, adding to
the mucus. They revolve round each other
swinging from their trapeze. They both engorge
their male sexual organs which flare out like
parachutes, shining bluish white and much
wider than the slugs themselves. These
parachutes twist about on each other and fuse,
with a process of sperm exchange taking place.
After that, these remarkable excrescences are
reabsorbed and the slugs separate and find their
way back to the tree – a weird, out-of-thisworld
performance.
All slugs have a large fold of flesh behind
the tentacles. This fold is the ‘mantle’ and
under it is a space used as a lung. The entrance
to the lung is on the right hand side of the body.
The nature of this mantle fold helps to separate
the slugs into two families. In most of the
Limax family the fold is marked with ripples
like a thumb print and the lung opening is
towards the hind third of the mantle. In the
other, the Arion family, the mantle is covered in
granules arranged haphazardly and the opening
is in the middle of one side. Another major
difference is that the slugs of the Limax family
have a ridge or ‘keel’ along part or all of the
back. All the body organs are confined to the
region of the mantle. The sex and excretory
openings are very close to the lung opening.
The rear part of the creature is almost entirely
composed of muscle. The tentacles carry the
simple eyes. The mouth has a continually
growing structure which is more or less a living
file – with its rough surface the creature rasps
away at its food.
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Downtime 
