Spiders check weather before take-off

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(NC&T/BBSRC) By casting a silk thread into the wind spiders can ride the currents for distances ranging from a few metres to hundreds of miles, carrying them out of danger or into new territory. But scientists have puzzled over why 'spider ballooning' peaks during spring and autumn but declines in windy and sunny weather, when sunshine produces more updraughts helpful for take-off.

A research team at Rothamsted Research, a sponsored institute of the Biotechnology and Biological Sciences Research Council (BBSRC), has developed a model showing that light breezes and moderately warm weather - typically in spring and autumn - provides the best spider ballooning conditions.

The team of biologists and mathematicians found the best flight weather by calculating travelling distances under different conditions of wind and sun. Hot days will produce more updraughts but without sufficient wind the spiders are not able to drift anywhere. On the other hand, if the wind becomes too strong the updraughts are disrupted, making flight impossible.

Since spiders prey on pests like mites and aphids, predicting spider ballooning peaks is important for crop management, explains Dr Andy Reynolds at Rothamsted Research. "Each day of the growing season around 1800 spiders land in each hectare of arable farmland after ballooning. If the farmers can predict the influx of spiders, they can reduce the amount of pesticides accordingly," says Dr Reynolds.

Two male Erigone spiders on a grass seed head. The lower one is in a pre-ballooning posture ready to disperse, known as the 'tip-toe' position. (Photo: Rothamsted Research)
The research team is planning field experiments to test the model, which could be relevant also for other organisms using the wind for transport, including mites and viruses.

Professor Julia Goodfellow, BBSRC Chief Executive, said: "This research is a good example of interdisciplinary collaboration, where biologists and mathematicians together have produced new knowledge which can help lead to environment-friendly pest control."


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