Invasive alien species in Switzerland - Schweizer ...

5 > Spiders and Allies – Arachnida 109
5.6 «Banana spiders» and terrarium species
Since the species introduced by trade in bananas and other tropical fruits (see e.g.
Schmidt, 1971) cannot establish populations in our climate, they are only of medical
interest, because they include some dangerous members of the family Ctenidae from
South America. Pesticides used before or during transport will often lead to the death
of spiders en route or shortly afterwards (pers. obs. by T. Blick of a ctenid which
arrived in Bayreuth, Germany in a consignment of bananas from Brazil).
However, some of the many stable populations of spider species in greenhouses are
probably the result of such introductions with trade. Thus, it is possible that poisonous
species, especially small ones, including some dangerous for humans could be accidentally
introduced and established in greenhouses (see, e.g., Huhta, 1972).
Spiders appropriately kept in terrariums are of no concern, but escaped specimens
should be handled with care, since the bite of some species (although not many) can be
dangerous for humans. If they escape into the wild they will die when temperatures
drop, since all species are of tropical or subtropical origin.
5.7 Discussion and recommendations
Monitoring spider species currently expanding their range after introduction, and
surveys at places prone to introductions, are recommended as elements of an early
warning system. This would allow the spread of the alien species to be followed and
document any displacement of native species. Some species are invading, but there is
no way of evaluating their potential threat to native biodiversity. The data collected on
synanthropic spiders in Switzerland, as well as other Central European countries, are
too limited to allow any conclusions to be drawn. Some cases of established tropical
species and increasing trade indicate the possibility of venomous spider species arriving
in Switzerland. If a venomous spider becomes established, the public would need to
be well-informed about how to handle the situation and anti-venom kits should be
made available.
Furthermore, to document threats to native species in natural habitats, the establishment
of long-term surveys in specific habitats is recommended. Without further studies
on alien spider species, potential impacts are only guesswork.
Surveys for synanthropic alien spiders and their relatives are of lesser importance, as
long as no dangerous spiders are introduced and the species that do arrive cannot
become established outside. Thus, the costs of conducting surveys for these would
probably not be justified. However, monitoring of some selected species (e.g. Oecobius
maculatus Simon and Zoropsis spinimana) to document their spread would be both
worthwhile and manageable.