A deadly lure? Department of Life Science, Tunghai University

You might call it a web of deceit: the webs made by one spider exploit a visual effect to entice nocturnal insects, which then become stuck in the silky threads. Such “lure and trap” dual-function spider webs have never been seen working at night before.

The lace sheet weaver (Psechrus clavis) is commonly found in low to mid-elevation subtropical Asian forests. It builds its large horizontal webs just above ground level in shady spots.

I-Min Tso at Tunghai University in Taiwan and his colleagues noticed that the silk is highly reflective, giving the web a whitish appearance that may be visible to insects at night.


To test whether this had any effect – either advantageous or disadvantageous – on the number of nocturnal insects caught, Tso and his team removed the spiders from 51 webs and used charcoal powder to blacken 22 of them, reducing their reflectance.

The team found that the untreated spider webs attracted significantly more prey than the blackened ones.

“Spider webs are not usually considered as potential prey lures,” says Tso.

False open spaces

Tso’s team speculates that the spiders’ chief prey – moths – have relatively poor eyesight and might mistake the whitish web as an area of open space in the otherwise dark and dense forest. Moths are attracted to such bright, open spaces.

The study isn’t the first to suggest that spiders resort to optical trickery to attract prey. Some add yellow pigment to their silk, which may attract insects given that many flowering plants produce yellow pollen. Other spiders use their bodies to reflect light and attract prey. But these visual tricks have so far all been seen working during the day. The new study is the first evidence of spiders using their webs for visual attraction at night.

“[It offers] a new perspective in understanding the foraging strategies of nocturnal animals,” says Tso.

A female Psechrus spider Department of Life Science, Tunghai University

Thomas White at Macquarie University in Sydney, Australia, says the study adds to evidence that spiders can lure prey into their traps. “We know many nocturnal insects like moths and bees have perfectly good vision at night – even colour vision, unlike humans.”

That said, he thinks it’s probably the general “brightness” of the web rather than its colour that attracts the moths.

“It would also be neat to see if they are attracting the attention of [spider] predators like nocturnal birds, but recording predation events in the wild takes a lot of patience,” he says.

Tso thinks the nocturnal lure strategy may also be used by other animals. “We will perform field experiments to test the hypothesis in the near future”, he says.

Journal reference: Animal Behaviour, DOI: 10.1016/j.anbehav.2017.06.016

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