Sluggin' Along: Mating Slugs: Courtship

Type D: Precopulatory behavior occurs, but mating never takes place. The reason is unclear: based on some unidentified criteria the pairing is broken up. Couple 18 is a good example of this.

You see that courtship begins with the customary trail following.

But once the lead slug turns back to initiate circling, an encounter similar to that in precourtship occurs, where the two slugs touch cephalic tentacles, as if to identify each other once again.

However, as you'll notice, instead of resuming courtship, the lead slug retracts its tentacles slightly, as if in deference to the follower, and the follower then precedes to move away, leaving the lead slug in a pitiful state of confusion.

The rejected slug starts to follow the one that is leaving, but as it turns around, it comes in contact with its own tail and possibly assumes it to be the tail of another slug, for it proceeds to follow its own tail, circling round and round and round. I couldn't help but break into laughter, it was so pathetically humorous. Remember that slugs are virtually blind and rely more on touch and scent, although you'd think a slug would be able to recognize its own body...

Type D can also occur in the opposite way, where the lead slug appears to want to participate in entwining but proves to be the less willing of the two, and the follower's advances are not reciprocated, as in Couple 23, shown below.

You can see that the follower becomes the dominant slug and extrudes its genitalia first, but the slugs' gonopores are not aligned and it appears that the other slug does not evert its genitalia.

Look closely at the slug on the left. Part of its genitalia is protruding from its body.

The result is a one-sided pairing, where the now-dominant slug can only attempt to mate with the other. After studying the photos, it seems the only thing exchanged between the two was mucus, not sperm.