Poisonous spiders gaining ground in Europe

Written by Dr. H. P. Bustami

Sunday, 18 November 2007

Scytodes thoracica (5 mm) a tropical specie now living in houses all over Europe. (P: Jørgen Lissner)

Since ancient times mans trade activity gave rise for migrating species from continent to continent. Nowadays combined with climate change new spider species are arriving in Europe. Every other year taxonomists find a new spider from other continents. Main source for that distribution is the global trade. The invasive spiders in average exceed european spiders in size and live within in buildings. Thus with more and more poisonous spiders the danger for humans rises with each year. In the last 150 years some 87 new spider species have been discribed due to a study of the Zoological Institute, University of Bern, Switzerland. These results of Wolfgang Nentwig and Manuel Kobelt recently were published in "Diversity and Distribution".

Bigger spiders better survivers

A direct linear correlation between number of spiders and rising world wide trade is evident. In ship containers tropical and subtropical spiders survive the more and more quick and large traffic between countries. The biggest specimens are among those animals which bear good enough the stress of the transport. This is causing a "natural selection" already during transportation as "stowaways" towards even larger specimens as founders of new populations.

Most species stemming from Asia

Only 3 species stem from South America, four from Australia and 80 from Asia. The intense exchange between Europe and Asia and the fact that many regions in Asia provide similar climatic conditions as in Central Europe favoured in the past the arrival of asian species. But climate change will bring more and more spiders from warmer regions including more and more poisonous ones. So the authors predict for the future at least one new spider specie every year. This is a cautious estimation because spiders are difficult to discover and the number of spider specialists is limited.

Since 75% of all new spider species live in urban areas and in houses people here maybe have to get used to new unbidden lodgers.

One business sector for sure will benefit from the new "illegal immigrants" to Europe: Psychologists specialized in the therapy of arachnophobia.

Source: Kobel & Nentwig: Alien spider introductions to Europe supported by global trade. Diversity and Distribution; 4-Oct-2007, online publication. doi: 10.1111/j.1472-4642.2007.00426.x

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