MadSci Network: Zoology

Re: How do slugs reproduce?

Date: Wed Jul 25 10:29:51 2001
Posted By: Aydin Orstan, Staff, Office of Food Additive Safety, Food and Drug Administration
Area of science: Zoology
ID: 995976124.Zo

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 

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

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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