Environmental Engineering Reference
In-Depth Information
beverydifficulttoseeamongthegrassstems.Likethetruecricketsthebushcrickets'sing'byraisingthe
wings and rubbing them together, but in these insects the left wing carries the teeth and lies on top of the
right wing.
Thecommonbluebutterfly Polyommatus icarus isverynumerousinsomeyears,withalargenumber
on the wing from June to August. Other butterflies found in the fixed dunes include the brown argus,
grayling, dark green fritillary and marbled white Melanargia galathea (Figs 81 & 82). Whiteford is also
one of the few Welsh localities for the grass eggar moth Lasiocampa trifolii , which is on the wing in
August and early September.
Like the shingle beaches, the sand dunes are rich in spiders, although these invertebrates are often
overlooked because their colour and markings blend so well with the background. The most common
spider found on the bare sand is the wolf spider Arctosa perita , a straw-coloured animal with diffuse
black, brown and orange markings and two pairs of white oval patches on the abdomen. Wolf spiders are
normally nomadic, active, ground-living spiders that actively hunt and pursue prey, without the help of
a web. They usually attach their eggs to their spinnerets and carry them around with them. This species
is an exception, however, and lives in a burrow in the sand, probably to protect itself from desiccation.
It is itself preyed on by a small grey hunting wasp, the coastal spider-hunting wasp Ceropales maculata ,
whichcanoftenbeseenflyingbackwardsandforwardsacrossthedunesinsearchofthespideroritsbur-
row.The wasp stings the spider and buries it with an egg, as foodforthe larva that subsequently emerges.
Another spider of the dunes that hunts without a web is the crab spider Philodromus fallax , named for
the crab-like shape of the body and its habit of moving sideways like a crab. Instead of actively pursuing
prey like the wolf spider the crab spider waits quietly and ambushes passing prey. On the marram grass
itself the most common spider is another crab spider, Tibellus maritimus , although this is not confined to
dunes. A great variety of money spiders can also be found including Ceratinopsis romana , a small dark
spider which is quite rare and confined to sand dunes in the southwest of Britain, but which is abundant
in Gower.
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