https://www.economist.com/science-and-technology/2018/11/08/town-dwelling-spiders-are-not-afraid-of-the-light?fsrc=scn/fb/te/bl/ed/towndwellingspidersarenotafraidofthelightevolutionIch hoffe, der Artikel ist auch lesbar, ohne dass man ein Konto eröffnet, falls nicht, habe ich den Text unten angehängt.
LG, Eckhart.
Title: Town-dwelling spiders are not afraid of the light
That lets them weave their webs in streetlamps
Economist Nov 8th 2018
Most spiders avoid light because, besides being predators, they are also potential prey. But there is a set of circumstances in which living beside a powerful light is an advantage. This is when you are a web-weaving spider. Moths and other insects are attracted to sources of illumination such as streetlights. Those are found predominantly in cities. It would therefore make sense if urban web-spinning spiders had lost their photophobia, so that they could more easily set up shop beside such lights. And an experiment by Tomer Czaczkes of the University of Regensburg, in Germany, suggests that for at least one species this has happened.
Dr Czaczkes’s interest in whether city life shapes spiders’ behaviour began when he saw lots of fat, happy arachnids building webs near Regensburg’s streetlamps. Delving into the academic literature, he discovered that urban moth populations have been shown to be less attracted to lights than are their rural relatives. Presumably, this is because, besides any webs involved, the whole business of flying round and round such lights is a fitness-reducing waste of time and energy. He reasoned that a similar but reverse sort of logic—resulting in their being more attracted to lights, or at least less afraid of them—should apply to town spiders versus country ones. And, as he reports this week in the Science of Nature, it does.
He and his colleagues collected egg sacks laid by their chosen animal, Steatoda triangulosa (the triangulate cobweb spider—selected because it is common throughout Europe and thrives in both urban and rural environments), from two sites in the Italian countryside, and also from Milan, Munich and Nice. The resulting 783 spiderlings were placed individually into boxes that had a dividing board through the centre. One side of each box was lit by a lamp that shed no heat. The other side was left dark. Two tiny gaps in the dividing boards permitted the spiderlings easy access to both sides of the box. Spiderlings were placed at random in the light or the dark at the start of their time there, and then monitored to find out where they built their first web.
Almost two-thirds of rural spiderlings built their webs in the dark part of the box, but only half of their urban cousins did so. That suggests rural spiders are indeed photophobic while urban spiders, though not actually attracted to the light, have ceased to be afraid of it—not so much Steatoda triangulosa, then, as Steatoda luminosa.
