Snails that arrive uninvited

Snails travel as eggs in soil, as small juveniles on nursery plants, and as adults tucked into a crate of stone or tile. They do not have to crawl the distance. Horticultural trade is a dispersal system, and hermaphrodites make it efficient, because one animal that has already mated can lay a founding clutch. This is how the garden snail became a near-global resident of temperate beds, how various slugs have traded continents, and how apple snails and giant African land snails have started outbreaks far from the countries they evolved in.

The useful habits are ordinary. Look through the soil of a new plant, including the drainage holes and the outside of the root ball, before it goes into the ground. Put unwanted eggs in a bin, not in the gutter, which is a river. Do not release a snail from a purchased pot into the garden if you cannot name it. Do not post live snails to friends. Do not release a classroom or aquarium animal at the end of the year. The sentence “it is only one” is how establishments begin, especially when that one can lay fertilized eggs alone.

If the animals already in the bed are common local species, the response is gardening rather than biosecurity theatre. Pick them at night, water in the morning so the surface dries, and protect the seedlings. If the animal is very large, or it is laying bright pink eggs above the water, or you simply do not recognize it and it arrived with a tropical plant, identify it before you decide. A photograph of the shell from above, of the aperture, and of the living animal is what a local extension service or natural history society usually needs. Do not mail the live snail unless the recipient has asked and the law allows the journey.

A week of quarantine is a pot on a saucer, kept off the soil, and looked at each evening. It catches more uninvited snails than any gadget sold for the purpose.