Slugs are hermaphroditic, possessing both male and female organs; most species mate, however, with one slug pursuing the slimy trail of another. If a slug is in mating mode, there is a chemical that is present in its slime that conveys this information to other slugs. When two receptive slugs first encounter each other, there can be extensive interaction prior to mating. The pursuer often mouths the tip of the tail of the slug it’s pursuing (see photograph) to confirm that it’s receptive. The pursued slug may shake its tail vigorously to signal that it’s not interested, in which case they go their separate ways. If the leading slug is receptive, however, mating eventually takes place, with sperm being transferred from each slug to the other through penises that extend half the length of their bodies. During this process, the sexual organs are entwined; occasionally, in some species, the organs get stuck. If this happens, one slug gnaws off the other’s penis in a process called apophallation. The penis is not replaced and the slug lives the rest of its life as a female. (The opening you see on the side of the slug is its respiratory opening, or pneumostome.)
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Most terrestrial snails are herbivorous, feeding on a wide range of vegetation. The snail’s mouth is on the bottom of its head near the shorter pair of tentacles. Snails (and all molluscs) consume their food not with mouthparts, like insects, or teeth, like mammals, but with a rasping tongue or radula. Snails don’t bite their food, but rather, rasp or scrape it. The radula is covered with rows of tiny “toothlets” which rasp particles away from vegetation and move them back towards the snail’s gullet. Different species of snails have differently-shaped toothlets. The radula is used by the snail not only to process food, but to clean bits of dried mucus from its shell. Supposedly if you listen hard, you can actually hear a rasping sound when the latter is occurring. (If you look hard, you can just barely see the orange radula of the land snail in the photograph.)
This morning I discovered the exoskeletons of nine millipedes clumped together at the top of a rotting stump. They were covered with slug slime, with said slug still at the scene. Presumably its stomach was full of millipede innards. If anyone can explain this phenomenon to me, I would be most grateful!
If you spend enough time looking under rotting logs, you’re bound to come across the tiny, pearly white eggs of a slug. With the right climate conditions, slugs will mate and lay eggs twice in a summer — once early in the spring, and once in late summer. Thirty to forty days after mating, the female slug lays her eggs under leaves, mulch, or in some other cool and moist location. They will hatch in 10 to 100 days — the length of time slug eggs take to hatch depends upon the temperature – the warmer it is, the faster they hatch.