Stumbled across your site while looking for official names for "Hummingbird Moths". I took this photo many years ago and always wanted to know what these slugs are doing on the front of my house. I am assuming they are mating but need conformation. Thanks for the interesting website,it is now in my favorites.
I think your slugs are redefining the exchange of bodily fluids. Slugs are hermaphroditic as well, each containing the organs of male and female. So a slug can mate with any other slug it meets. Awesome image and a welcome addition to our new Love Among The Bugs page.
Those mating slugs on Bug Love page From:
Hi nice bug people, I love your site. I thought you might like to know that the pair of mating slugs are Limax maximus, the Leopard slug, which is an introduced species in the USA. Like all pulmonate gastropods, they are hermaphrodites. This large species is quite common around human habitation. You can see another picture, but not nearly as good as the one you have, at: www.fcps.k12.va.us/StratfordLandingES/ Ecology/mpages/leopard_slug.htm And there is a whole sequence of picture of a pair mating at: http://members.optushome.com.au/awnelson/davidavid/slug/ Although I am primarily a mollusk person, I also am fond of bugs. Invertebrates rule!
best to you,