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Slug Mating Behavior

9-2-13 slugs 035Slugs 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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7 responses

  1. Cindy

    Why do they look so different? Age? Do different species mate? Maybe slugs blend with their surroundings? Thanks for all your help teaching us to notice and appreciate the smaller things out there in the natural world! — Cindy

    September 3, 2013 at 1:01 pm

  2. dellwvt

    Who knew? What a story! Amazing information once again. Thanks, Mary!

    September 3, 2013 at 1:02 pm

    • Hi Cindy,
      I’m afraid I don’t know the answer to your question about their differing appearance. They are the same species…maybe age-related?

      September 3, 2013 at 1:32 pm

    • Thanks so much, dellwvt. I was afraid it might be too x-rated for wordpress to publish!

      September 3, 2013 at 1:33 pm

  3. Kathie Fiveash

    This is fascinating! Here’s another x-rated piece of natural history for you all. I was doing some research last year into barnacles, which are crustaceans and, like slugs, are hermaphroditic. They must solve the problem of how to mate with another barnacle while firmly attached to a rock. Barnacles accomplish this by having the longest penis, relative to body size, of any animal. It is as much as eight times as long as the body, long enough to stretch over to a neighboring barnacle to deposit a sperm packet. With barnacles, mate selection is all about proximity. A mated barnacle stores the sperm packet separately from the eggs, fertilizing the eggs when conditions are right. He/she then holds them inside the shell after they hatch until there is adequate food in the water. Then the larval barnacles float away in the plankton.

    September 3, 2013 at 2:41 pm

  4. nangalland

    Who knew???!!!! EEWWW! XO- Nan

    September 3, 2013 at 10:41 pm

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