DREIJERS, E, REISE, H. & HUTCHINSON, J.M.C. 2013. Mating of the slugs Arion lusitanicus auct. non Mabille and A. rufus (L.): different genitalia and mating behaviours are incomplete barriers to interspecific sperm exchange. Journal of Molluscan Studies79: 51–63.
In this one-minute video we see an individual of Arion vulgaris (top left, redder individual) at the end of a copulation with Arion ater. Intraspecific matings of A. ater last only half the time as long as those of A. vulgaris, so the A. ater individual is already trying to separate and has retracted its genitalia whilst the A. vulgaris individual is still stationary. Nevertheless both have already prepared a spermatophore, and we can observe as they separate that both partners receive these tube-shaped structures. At the end of the video the tail of the recieved spermatophore is still visible sticking out of each genital pore. Please read the article for further details (but note that in it A. lusitanicus = A vulgaris and A. rufus = A. ater). It is the same copulation as illustrated in Figure 1.
If you would like to examine these videos frame by frame, we recommend VirtualDub2. The necessity for dim lighing (so as not to disturb the slugs) explains the grainy quality.
Click on picture below to start/stop video (1.1 MB download)