Every gardener knows the temptation — you find snails ravaging your petunias or your lettuce patch, and rather than resorting to chemicals or messy beer traps, you sling the snails into your neighbour's garden and hope they won't come back.
New research shows that this is exactly the right approach — but only if you can throw far enough. Snails appear to have a homing instinct over short distances, as proved by a famous experiment in that involved moving snails from the garden they were found in.
But research published on Friday shows this homing instinct can be overcome for many snail populations. If the pests are removed by at least 20 metres from their home patch, they will largely be unlikely to return. The finding opens up the delightful prospect of "snail wars" among gardeners, vying to lob the gastropods the furthest distance possible in order to keep them off.
Beware, however, that even if you manage to remove a large proportion of the blighters, they are likely to repopulate your herbaceous borders alarmingly quickly. The waves move much faster than the snail itself, and generate enough force to push the snail forward. Lai found out that these muscular waves are sufficient to propel the snail forward on a flat surface, without needing the special mucus to provide more traction.
The mucus does help the snail stick to surfaces, however, and comes in handy when traveling up a wall or across a ceiling, upside down. Lai shot high-resolution videos of crawling snails and used a laser to measure how the muscle waves moved back and forth and up and down on a snail's foot.
She also measured the forces that a snail generated when crawling on a gel. Her detailed measurements of how snails move could help other research groups that work on snail-like robots.
Researchers discovered nearly 30 years ago that snail mucus has some unusual properties. It allows the animal to stick to a surface while moving, with the mucus changing its characteristics according to how firmly the snail presses on it. The slime initially acts like glue, sticking the snail to the surface. But when the snail's foot presses down hard enough on the mucus, it becomes more liquid, allowing it to flow underneath the moving snail.
Existing theories assumed that this special characteristic of snail mucus was always necessary for the snail to push off and move forward. But Lai and her coworkers, professors Juan C.
Lasheras' lab had previously developed tools to study the movement of cells. He studied the movement of a single-cell amoeba as a model for how human cells move during development, during immune responses, and when rebuilding damaged tissues. Lai adapted Lasheras' tools to study snails and slugs. Snails are similar to our cells "in that they both have to move and adhere to a surface at the same time," she said. Lai's experiments echoed Eadweard Muybridge's famous stop-motion photographs from the late s.
His photos — taken on what is now the Stanford campus — proved that all four of a horse's hooves are off the ground at the same time during a gallop.
In Lai's case, she used high-resolution videos to show that parts of a snail's foot lift off the ground as the waves of motion travel through it. If the snail's foot never lifted off the ground, then the animal would need the special mucus to achieve enough force to push itself across a horizontal surface. Do red crabs move fast or slow? Is a land snail faster than a sea snail? Does snail move faster on dirt or sement?
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