Cardiff University, UK, scientists, led by Dr Bill Symondson in the School of Biosciences, have become the first to use DNA-based techniques to analyse the content of spiders' guts to identify the prey they have eaten in the field.
Money spiders – or Linyphiidae - are a vital controller of pest numbers on farms because their prey includes aphids. However, aphids have poor nutritional value and are sometimes toxic, so the spiders need to balance their diet with other prey.
In a field experiment, the Cardiff team's analysis showed that the money spiders were eating large numbers of small insects called springtails or Collembola. Stomach contents showed that they were eating several different species of Collembola, but with strong preferences – DNA from a species, which was uncommon at the site where they were collected, proved to be present most frequently in the stomachs of the spiders.
"The DNA analysis enables us to identify precisely what the spiders have eaten," said Dr Symondson. "If we compare that with the prey populations in the field, we can see which prey the spiders prefer to eat when they have a choice."
"If we can encourage this prey insect in greater numbers, it should boost the population of spiders and therefore provide better control of aphids," said Dr Symondson.
Spiders, and in particular money spiders, are extremely important in the control of pests in arable crops, and their webs often cover more than 50% of the fields they inhabit.
However, the team is also using the techniques they have developed to analyse other important predators, such as the ground beetle, whose prey include slugs – the most damaging of crop pests in Europe.
"Many people are surprised at how important such natural predators are in the control of pests," said Dr Symondson. "Even on a conventional farm, which uses chemical pesticides, most pests are controlled by predators most of the time.
"Regulations are placing increasing limitations on the use of chemicals, so encouraging natural predators is going to become even more important."
Journal
Molecular Ecology