Threads that make up the orb-web of the cross spider experience deformation when a positively charged insect enters the neutral or negative field through electrostatic attraction.

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Cross spiders, also known as European garden spiders, belong to a group of spiders that are known for constructing orb-webs. An orb-web experiences crossing in the center; please see the gallery for an example of an orb-web. It is believed that the silk threads of orb-webs remain at a neutral or slightly negative charge. Insects, such as honeybees, can collect positive charges when flying through the air or interacting with areas of high positive-ion concentration. If an insect develops a positive charge and flies or walks past an orb-web, the opposite charges interact electrostatically causing an immediate attraction. Threads on orb-webs of the cross spider have been observed to deform from their regular shape as a positively charged insect passes by. This may provide insight in a more sustainable way to capture pests in our gardens and maybe someday even our farm fields (without the use of harmful pesticides).

To see for yourself, please view the research video Edit Summary

References

"...We show under laboratory conditions that electrostatically charged honeybees, green bottle flies, fruit flies, aphids, and also water drops falling near webs of cross-spiders (Araneus diadematus) induce rapid thread deformation that enhances the likelihood of physical contact, and thus of prey capture." (Ortega-Jimenez and Dudley 2013:1)
 
"Video sequences of positively charged insects and water droplets falling towards a grounded orb web reveal rapid and substantial web attraction (Supplementary Movie S1 online). Radial and particularly spiral silk threads are quickly attracted to the electrified bodies. By contrast, control trials using uncharged insects...and drops...show no such deformation (Supplementary Movie S2 online)." (Ortega-Jimenez and Dudley 2013:1)

"Electrostatic forces have been previously proposed to play an important role in silk adhesion, although experimental evidence indicates that only non electrostatic adhesive properties pertain to cribellar silk...Experiments show clearly that positively charged insect bodies induce rapid attraction of silk threads in the webs of cross-spiders, indirectly supporting a prior hypothesis that static charges of insects increase the prey capture success of orb-webs. Risk of capture for a free-flying insect may correspondingly be enhanced given that the induced deformations observed here are comparable to the average mesh spacing for cross-spider webs (~2 mm). Observed deformations also suggest that greater charges and associated web displacements may characterize larger insects, and are more likely to induce deformation of multiple radial and spiral threads (Table 1). By contrast, length-normalized deformations suggest non differences among insects...The greater charge typically accumulated on larger test insects (see Table 1) reflects its direct dependence on both electric potential (as induced here by the Van de Graaff generator) and their capacitance. Electrostatic charge acquired by insects in free flight will similarly reflect these factors, but charge will principally be acquired through interaction between the flapping wings and the surrounding air, along with particular atmospheric conditions that promote charge accumulation (e.g., lower relative humidity)." (Ortega-Jimenez and Dudley 2013:2).

Journal article
Spiderweb deformation induced by electrostatically charged insectsSci. Rep.July 4, 2013
Victor Manuel Ortega-Jimenez, Robert Dudley


Spider Webs React to Electrically Charged Insects, Increasing Capture Chances VIDEO

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Organism
Garden Cross SpiderAraneus diadematusSpecies


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