Worm composting could be doing more harm than good to the environment, according to research in Germany.
"Worms produce a significant amount of greenhouse gases. Recent research done by German scientists has found that worms produced a third of nitrous oxide gases when used for composting," an expert was quoted as saying.
In an interview with a leading renewable resources journal, Jim Frederickson, senior research fellow at Britain's Open Universities faculty of technology, said the German research showed that worm composting has deleterious effects on the environment that should be considered more seriously.
Worms naturally produce nitrous oxide gases when they are put into the process of composting.
Worms can be used for home grown composting or commercial composting and are typically red worms. They are used to recycle food scraps and other organic material into valuable soil worm compost, otherwise known as vermicompost. This compost can then be used to grow plants.
"We have concentrated on getting waste out of landfill and into worm composting systems but they can actually produce more greenhouse gases than landfill sites produce," Frederickson told Materials Recycling Week, a leading publication for the recycling and waste-management industry.
In Germany and other environmentally aware countries, governments have supported the composting of waste in efforts to reduce the land filling of biodegradable waste. This includes encouraging householders to invest in home composting systems.
Although Frederickson says that worm composting is a positive thing, he claims that not enough research has been done on worms releasing polluting gases.
Speaking of worms, Frederickson told the magazine: "Everybody loves them because they think they can do no harm but they contribute to global warming. People are looking into alternative waste treatments but we have to make sure that we are not jumping from the frying pan into the fire.
"We need to investigate all alternative systems for greenhouse potential.
"The emissions that come from these worms can actually be 290 times more potent than carbon dioxide and 20 times more potent than methane. In all environmental systems you get good points and bad points."
This is because worms used in composting emit nitrous oxide - a greenhouse gas 296 times more powerful, molecule for molecule, than carbon dioxide.
Landfill sites produce methane, which is 23 times more powerful a greenhouse gas than carbon dioxide.
Red worms appear naturally in country compost heaps but over the past decade or so a thriving trade has grown up in domestic wormeries which enable people with space as limited as a balcony to compost their kitchen waste.
Domestic wormeries are dustbin-sized boxes formed from several trays, with names such as Can-O-Worms; into which reared worms are introduced. Some are even made to look like beehives, according to a report in The Daily Telegraph of London, which also cited the German research.
The worms are laid out on lime and vegetable peelings. When they have digested this material they move to another level in search of more food. The lower trays of compost can be used and a tap allows the liquid collected to be drained off as fertiliser.
The red worms used in composting are extremely efficient at breaking down decomposing material such as kitchen scraps and other organic material but they emit nitrous oxide in the process of digestion in the gut.
Frederickson told Materials Recycling Week: "The amount of worm composting is very, very small and the amount of landfill is huge. But landfill sites are quite well run these days and it is possible to extract about half the gas they generate and use it for electricity generation.
"So the amount of nitrous oxide emitted by large scale worm composting is something we should be looking at before we go further down that route."
Frederickson said that the research he and his colleagues had done was on very large commercial worm composting "beds" which build up large amounts of nitrogen that is then emitted by the worms as gas.