By Brendan Knapp
SLUGS and snails may not look frightening, but don’t be fooled. Poking out from beneath their slimy bodies is a tongue-like appendage called a radula, covered with thousands of tiny teeth. As gardeners know to their cost, this is a tool of extreme destructive power, which can shred stems and leaves like a grater. From dandelions to dahlias, few plants are safe.
Native slugs and snails are a vital part of ecosystems. They provide a food source to other animals, digest dead and decaying matter and eat pests. But invasive species can throw things off balance and it can be tough to control them.
Many gardeners have their own tried and trusted methods of attempting to make their plants safe from these gastropods, from the classic technique of circling the stem with crushed eggshells to the application of copper tape to flowerpots.
For professional growers, it isn’t just their plants that are eaten up, but their profits too. Six years ago, grower communities in Oregon had had enough and representatives from the grass seed, vegetable and Christmas tree industries demanded the state act immediately to stop invasive slugs and snails.
In response, the state called in ecologist Rory Mc Donnell, one of the world’s foremost slug and snail experts. For the past few years, Mc Donnell, now based at Oregon State University, has been looking for ways to control invasive slugs and snails and has developed an effective method.
He tells New Scientist about the toll of invasive slugs and snails and why the best way to control them is almost certainly already in your kitchen.
Brendan Knapp: How much damage do invasive slugs and snails cause?
Rory Mc Donnell: Without question, it is billions of dollars every year. There was a study done by the Oregon Seed Council in 2012 that showed slugs alone cost the grass seed industry about $60 million a year at the time. That is due to direct crop loss, the cost of molluscicide and the extra labour needed to sow more seeds. It’s just mind-blowing to me. But that’s the reason I have my position. And one thing that people often neglect about slugs and snails is that the damage they do isn’t limited to just eating crops. Snail mucus or slug faeces on the crops decreases the quality rating, which in turn reduces the overall price of the produce when it goes to market.
And that’s before we take into account the damage to people’s gardens…
If you’ve got a nice vegetable garden, if you’ve got lettuces, carrots, potatoes, even peppers, they are definitely going to be taken out by slugs and snails.
It is coming up to spring in the northern hemisphere. Are slugs and snails going to be emerging to eat plants soon?
Over the winter, most slugs and snails hibernate and, yes, as it warms up in the spring, they come out to feed. Then they activate a summer hibernation phase called aestivation, where they seek shelter again – slugs below ground; snails above ground. And then they come out again in the autumn. Here in Oregon, once we get the first fall rai