Black Widow Spider Webs: Insect DNA Can Be Extracted and Analyzed

With the help of DNA detection, researchers are learning valuable information about insects trapped in black widow spiders' sticky webs, according to a recent study published in the journal PLOS ONE. 

The DNA of a black widow's prey can remain detectable at least 88 days after the living organism is no longer present on the web. For their study, researchers from the University of Notre Dame studied the webs of three black widow spiders that were fed house crickets in order to noninvasively extract and examine mitochondrial DNA to identify both the spiders and their prey. 

Black widow spiders are considered one of the most venomous spiders living in North America, although only females are potentially lethal to humans, while males and juveniles are harmless. Females usually have a reddish hourglass shape on the underside of their abdomens, along with a series of red spots and markings on their underbelly. The spiders use their webs to trap prey such as flies, mosquitoes, grasshoppers, beetles and caterpillars.

"Sticky spider webs are natural DNA samplers, trapping nearby insects and other things blowing in the wind. We see potential for broad environmental monitoring because spiders build webs in so many places," Charles Cong Xu, one of the study researchers from the University of Notre Dame, explained in a news release. 

Scanning the DNA in spider webs is a less invasive alternative to "beating," which is when scientists shake a tree canopy until the spiders fall to the ground to be collected. Other collection methods also include vacuum sampling, sweep netting, pitfall traps, and visual searches. The new method, on the other hand, allows the spiders to remain in their natural habitat. 

While further study of field-collected spider webs is necessary, their findings have implications for conservation research and for determing which prey species are present in a certain area. 

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