Courtship in any animal has two functions – to ensure that mating takes place with a member of the same species, and to select the finest possible partner. So courtship involves species level identification and tests of vigour.
How do slugs mate?
The mating ritual of slugs may appear bizarre, but it has evolved to fulfil both of these functions. Slugs are hermaphrodites. During intercourse, each suitor simultaneously delivers a packet of sperm to its partner’s storage organ. To do this, they evert parts of their genitalia and lock them together.
More fascinating slug facts
In slugs, identification of suitable mates is first by smell, second by courtship behaviour and third by the unique interlocking devices developed by each species. The leopard slug Limax maximus and its close relatives copulate while suspended from a mucus pad.
This behaviour is one of the ways that slugs can ensure that they are mating with members of the same species. In addition, such exertions and the production of a lot of mucus ensure that intercourse only takes place between individuals at the peak of their physical condition.