They are to regular slugs as a dreadnought is to a destroyer -- the Great Gray or Leopard Slug. And several of them live in my back yard. Presumably several generations of them, though I haven't kept track.
This year's crop may be pretty good; being relatively bite-sized (several bites when fully-grown; they get to be much bigger than you'd expect, as large as a small snake and fatter) and relatively slow* they spend most of their time out of sight, but I have already had three encounters.
Several days ago, I turned over a fallen branch and found not only a camo-pattern slug as big as my thumb, but a whole clutch of wasabi-green slug eggs she† had just laid. I turned it back over and moded it to a safer spot.
Last night, I was dumping water from the big blue tarp and moving it away from the wild parsnip‡ that has taken up residence in a corner of the fence and which will meet my enforcer, Mr. Weedkiller, I found two more and larger examples, which were hanging on (they produce strong, sticky slime and even a large one can climb vertical surfaces) in various damp and shady folds. I made sure they were still in the shade and above the waterline as I moved the tarp; what I will do when the time comes to fold the thing up, I don't know. It's overdue for disposal but I don't want to reduce the population of slugs that hunt garden-eating slugs when I get rid of it.
* Unless you're a smaller vegetarian garden slug.
† It's complicated. Let us not delve into the private life and courtship of Great Gray slugs, which involves climbing to high places, hanging from a rope of slime and having terrifying knife fights.
‡ The wild parsnip is to the common carrot what a one-percenter biker is to a kid on a moped. Annoy a lively one on a sunny day and you're likely to end up with nasty chemical burns. While this gets somewhat panicky coverage by local TV and on social media, good-quality garden gloves, long sleeves and common sense go a long way towards avoiding the problem.
6 days ago