|MadSci Network: Zoology|
Dear Narindar, Slugs are air-breathing land snails (pulmonates) that have totally or partially lost their shells during their evolution. The largest slugs you are likely to find in your garden, appropriately named Limax maximus (the large gray ones with many black irregular spots covering their bodies), have a tiny vestigial shell buried within their mantles. The mantle is the shield-like hump covering the back of the slug's head. This shell, which can be seen only if a slug is dissected, is one of the clues that betray the slugs' evolutionary past. Slugs, like all other shelled-snails you are likely to find in your garden, are hermaphrodites (another clue to their evolutionary relationship with shelled snails). That means every slug has both male and female reproductive organs. Furthermore, they have only one genital opening that leads to both the vagina and the penis (the latter is normally kept inside the body). The genital opening is on the right side of their bodies under the mantle (the more easily noticed large hole thru the mantle also on the right side is the breathing hole). So, how do they reproduce? Some slugs always "outcross". This means that they always mate with other slugs of the same species. To bring their genital openings closer, two slugs come side by side facing in opposite directions with the right sides of their bodies against each other. If you keep looking for slugs, sooner or later you will come across a mating pair, most likely on a warm, humid night. Hermaphrodism always raises the possibility of self-fertilization. It turns out that some slug species indeed self-fertilize. In other words, they have done away with mating; instead each individual uses its own sperm to fertilize its own eggs. And to make things more intriguing (at least for the biologists who study slugs), some species sometimes outcross and sometimes self-fertilize. Slugs lay their eggs in places that always remain damp. You may find groups of them (yellowish- or greenish-white tiny balls) under rocks and rotting wood. Baby slugs look like their parents, except that they are smaller. Here is the Internet address of a page describing the research of a scientist who actually studies how slugs reproduce (it's a bit advanced though): http://wcc.ruc a.ua.ac.be/EvolutionaryBiology/Kurt.htm I hope your developing interest in slugs will turn you from an exterminator into a malacologist (a person who studies molluscs, which includes not only the snails but also their more distant relatives, the oysters, clams, octopuses and the like). Aydin Orstan
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