Key points
- Invasive introduced snails are a serious pest for cropping and we're looking for a way to stop them in their tracks.
- One way is using their likes and dislikes as a push-pull strategy.
- Garlic proved the most effective natural deterrent against snails in laboratory tests.
Invasive snails and slugs contaminate cereal and legume crops and cost the grain industry over $170 million each year.
We’re developing alternative management methods based on push-pull strategies by finding out what attracts and deters snails from crops. Our research will improve chemical, biological and mechanical control methods.
Snail fail: Introduced snails going beyond the pale
Four invasive snail species from the Mediterranean are key pests of grain and legume crops in Australia. They feed mainly on dead organic matter but can eat crops and pastures. Their mucus also contaminates plants needed for animal grazing. But their biggest negative impact is at harvest time.
In early summer, the snails climb to the top of plants to avoid hot soil temperatures and enter a form of hibernation. This coincides with the harvest of crops like wheat, barley and canola. Snail shells obstruct harvesting machinery and reduce grain quality.
Swiping for snails: red flags
Our entomologist Dr Valerie Caron led our research team in France looking at snail behaviour. They wanted to know what attracts (pulls) and repels (pushes away) snails.
“We knew that snails prefer the tallest and widest fence posts or plant stems to climb. This suggested that they were using visual cues,” Valerie said.“
And we knew that they were attracted to black, so we started playing with colours, looking for any preference between colours. We didn’t expect to see big differences because it’s generally thought that snails don’t have great vision and don't see colours."
Talented Master's student Cedric Kosciolek was chief snail wrangler. The dedicated team in France also collaborated with the European Biological Control Laboratory from the United States Department of Agriculture Agricultural Research Service (USDA-ARS).
“When we think about snails, and gastropods more generally, we expect them to be a boring subject,” Cedric said.
“But my internship at the CSIRO European Laboratory showed me the opposite! We saw behavioural differences between the four species. It just confirmed that the natural world is always full of surprise and diversity!”
Snail shell-abrations
Cedric built snail arenas in the laboratory to test for colour preferences. Snails were placed in the middle of the arena with different coloured strips around the outside. Each trial gave the snails a choice between black and a colour. We tested with red, green, purple, orange, blue and yellow.
“It was a huge shock to discover that they liked the colour red,” Valerie said.
The team compared red and black in the laboratory and then in the field. The snails still preferred red.
“Gastropods don’t have the ability to see colours in the way mammals do. And red doesn’t play an obvious role in food sources or warning colours for these snails,” Valerie said.
“It could be down to contrast. Studies have shown that red and black offer the best contrast with natural backgrounds.”
Blazing a snail of destruction
As for the “push” part, it’s no secret that garlic repels slugs and coffee repels some snails. Researchers tested these as barriers against our four snails.
“We found garlic was really effective and coffee was somewhat effective, under laboratory conditions,” Valerie said.
“This is likely based on their chemical composition rather than their physical texture.”
However, the team found results with coffee barriers were highly variable. Wet coffee grounds seemed to lose their deterrent capacity within 24 hours, compared to dry coffee powder. This could be due to lower caffeine content.
And the snails didn’t seem to mind the coffee grounds – they skated right over them and even ate them!
The slime and the place
These initial results are promising, but there’s still a lot of questions to answer before we can use push–pull technology to help manage invasive snails in Australia.
The best snail deterrent was garlic. Further study of what makes it effective and how it could be applied in the field is needed.
“We need to figure out if the barrier works long term, what are the active ingredients or key deterrent molecules, and how we could use these in the field,” Valerie said.
This was Cedric’s first research project on snails, and it was a great experience.
“I’d be happy to work with snails again, and there are still many things to explore with terrestrial gastropods,” Cedric said.
Using visual stimuli for gastropods is a new approach. Ultimately deploying coloured vertical posts around fields could allow farmers to capture and remove snails at the start of summer when they begin climbing to the tops of plants and posts.
“This is the first time we’ve tried to use their behaviour. It’s a very different approach. We’re using visual cues and chemical cues at the same time, which is unusual,” Valerie said.
Our work opens the door to further research new snail management strategies to reduce their impact on crops in a safe way for the environment.