This
article was written by ANTONIO ARIZA MORENO
<l95aa@tay.ac.uk> to offer some
clarification to the 'Media News' item in Vol1.
No 9. of Arachnids Weekly
The explanation for the lack of
'accidents' with Tegenaria agrestis (which is an
extremely widespread species all over Europe) is
the fact that it is a strictly rural species in
Europe, as indicated by its name. This species is
never found near human lodgings, gardens, towns.
etc... and can only be encountered in rural
places where there is little human presence or in
wild habitats where there is no human presence
whatsoever. Supposedly the reason behind this
lies in its cousin Tegenaria gigantea, which is
found all over Europe, inhabiting rural and
metropolitan areas with a high incidence of human
presence.
T. gigantea is an enormous spider
for European standards, being one of the most
aggressive species I know (which is no wonder
when we take into account its life style) and,
when confronted by the much smaller T. agrestis,
will usually win and make a good meal out of its
cousin. T. agrestis can't compete and its
presence is therefore relegated to fairly
inhabited parts of the countryside.
Even though T. agrestis bites are
almost unknown in Europe, T. gigantea bites are
fairly common, which is due to the fact that
these spiders are probably the most common
species in inhabited areas and that they are
found living in our houses all the time. This
species is able to go a very long time without
water, a very important factor since the inside
of a human home is among the driest places that
can be encountered, and without eating as well.
The last point may be crucial in explaining their
aggressive behaviour since they will not doubt
and attack anything that moves, even when it is
several times larger than they are (and, as I
said before, these spiders are already fairly
large) and this is essential if they want to
survive in the hostile environment they have
chosen to live in. When food is scarce, one has
to try to subdue and eat everything that comes
across one's path ... or, in this case, funnel
web.
It is a common sight to see males
of this species running over the carpet and
anything else in European houses from late August
until the first frosts and in flats like mine (on
the groundfloor with a garden in the backyard) it
is normal to wake up in the morning and find one
or more of them trapped in the bath or sink.
Their bite is very painful, which
is no wonder when you look at their huge
chelicerae (quite impressive for an araneomorph
spider), but no symptoms of extreme swelling and
necrosis of the affected tissue (normal symptoms
of T. agrestis bites and which are scientifically
known as 'Tegenarism') can be observed, even
though the bite may hurt for a few days.
When T. agrestis was exported to
the American continent, it found that it had no
competitors and could easily usurpate and conquer
the habitat it had been denied in Europe. Life
may not be much easier in human dwellings, but it
is much more comfortable, warmer and there are
definitely less predators than in the wild. It
seems that T. agrestis has been establishing
itself and spreading over the North American
continent for a much longer period of time than
T. gigantea, and even though the latter of the
two species may still win and get rid of the T.
agrestis menace, this may still take a long time
or not happen at all. The other factor that has
allowed its spread over the North West of the USA
and Canada is the fact that this species is very
well adapted to cold environments, much more than
other Tegenaria species and obviously more than
other Native species that could have represented
a threat to it, like the different recluse and
widow spiders. Hence, since competition is almost
non-existent, there is little that can be done to
stop it from spreading further and further south.
By the way, I've always kept some
T. gigantea (or at least I think they are T.
gigantea, there is much confusion about this
genus and many of its species are extremely
similar) and still have two huge females. Each of
them has produced over six fertile eggsacks this
year and I'm using the spiderlings to feed my
Cyclosternum fasciata spiderling, one of the
smallest tarantula spiderlings that I've ever
seen.
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