|MadSci Network: Zoology|
What a super question! After much reading (and sorry for the time taken to do so), it appears that land snails and slugs (both called 'gastropod molluscs') have two potential ways to communicate to members of their own kind, or species. If you have any live snails handy (best time to look for them is after rain in early summer), take a look at their head and face area. You should be able to see two pairs of tentacles. The top ones are longer and have simple eyes on the end. It has been found that they are really only good at seeing large objects - like a bird coming to eat them. Thus they don't likely use this to communicate with each other. However, the lower tentacles are used for touch and chemical reception (like the ability to taste in humans) - which would be valuable for two snails when they meet. If they decide to mate with the snail they meet, they will exchange 'love darts' (much like being shot by a cupid's arrow) to identify the species they belong to (but not whether they are male or female, because snails are hermaphrodites and are both male and female at the same time). If the love dart is received by the right partner, courtship will proceed. If you watch a snail exploring it's environment, it will wave all it's tentacles through the air to pick up as much information from the air as possible. But there is another way to communicate that is often overlooked. The slimey mucous trail that snails and slugs leave behind when they slide from one place to another is a great place to leave behind a semi-permanent message for a passing snail to cross over and 'read'. The use of a special chemical signal called a pheromone (which is much like a perfume but made of hormone-like substances) has recently been studied by scientists. Pheromones are left behind, mixed in with the slime trail. In 1992 a scientist named E. Pakarinen wrote a research paper on communication of stress (from being pecked at by a bird) through slimey pheromone trails. If I remember correctly, it was found that a snail sliding upon the trail of another snail that had been stressed made it move away as quickly as possible - a good reaction if there is a chance the bird is still around. You can check this for yourself in the Journal of Animal Behavior, volume 43: pg. 1051-52. Happy gastropoding! Neala MacDonald Zoologist and Science Outreach Coordinator University of Western Ontario London, ON, Canada
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