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Pierre, check the soil for little round eggs that look (unfortunately) like timed release fertilizer. That is what slug eggs look like. I live in the Northwest where we have slugs bigger than you can imagine. I know this because I lived most of my life just outside of Boston. But, you might also have just had a lone slug that had slithered its way into your pot. The eggs hatch in the spring so that is when you should start watching for more. They love beer, so you can try trapping them in a saucer where they will drown in the beer. Yum!
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