New York

Spiders' silken webs are death traps for many insects. And now scientists have discovered DNA left on a web can be used to identify its owner and their victims, much like a crime scene.
As well as revealing a spider 's last meal, the research could be used to monitor endangered species or to track down spider pests. While there are many methods of monitoring spider populations, the majority are time consuming and rely on experts being able to find and identify elusive species.
This new method of analysing web DNA could make it easier for ecologists to pick out a species quickly from some 45,000 in number. The study, by the University of Notre Dame, examined black widow spiders kept at Potawatomi Zoo, also in Indiana.
Lead researcher Charles Xu, a Masters student in Evolutionary Biology, extracted, amplified, and sequenced mitochondrial DNA from spider web samples of the spiders.
He found web DNA reveals which spider species made the web and what it had eaten in the weeks before.
As the spiders in the experiment were fed on house crickets, Dr Xu detected traces of cricket DNA.
The study, published in the journal Plos One, says: 'Spider and prey DNA remained detectable at least 88 days after living organisms were no longer present on the web.'
Spider webs could therefore be used to monitor the environment in the future, with the help of metabarcoding technologies, which profile the DNA of all organisms in a sample.
Xu told Gizmodo: 'Since spider webs are basically these large sticky traps that are picking whatever might be blowing around, metabarcoding spider webs could be used to reveal entire communities of organisms in a variety of different environments.'
The study said: 'Spider web DNA as a proof-of-concept may open doors to other practical applications in conservation research, pest management, biogeography studies, and biodiversity assessments.' He said the next step is to look for DNA from numerous spider species in a range of habitats to understand how useful spider web DNA is under different conditions.