24 April 2006

Tiny slug’s last meal


Saturday morning I saw several really small slugs under the wet rocks in my backyard. This one, barely 5 mm long, was one of them. It is definitely a juvenile, because there are no known species of slugs, at least in the eastern U.S., that don’t grow larger. I suspect this slug was either a Deroceras reticulatum or an Arion intermedius.

Later, while looking at the pictures on the monitor, I noticed the patches of green visible thru the slug’s body (arrows in the picture below). Slugs don’t have green organs. So, I believe what we are seeing is what the slug had eaten, probably some algae growing on the rocks.


Compare the positions of the green patches with the positions of the stomach and the upper part of the rectum in the drawing below. I think it is safe to assume that the lower arrow in the slug picture is pointing at the stomach and the upper arrow is to the upper rectum.

Generalized representation of the digestive system of a pulmonate slug. Figure is from Barker, G.M. 1999. Naturalised terrestrial Stylommatophora. Fauna of New Zealand. No. 38.


Tim Pearce said...

The tiny slug looks more like Deroceras, not Arion. Arion would have a mucus pit visible at the tail, and a less pointed tail. The pneumostome is not visible in these images, but would be in the front half of the mantle of Arion, but I suspect it is in the back half of this specimen (so it would be Deroceras). Furthermore, as a transparent slug, you can vaguely make out the internal shell (about 1/5 the length of the mantle) at the back end of the mantle (just forward of the yellow arrow in the second photo, or just forward of the three white light reflection spots on the first photo). Deroceras has a solid, plate-like shell, while Arion has a cluster of calcium carbonate granules. It is likely to be a juvenile of Deroceras reticulatum, the most serious molluscan agricultural pest world wide.


Tim: That's a very good analysis. But I am not sure if that white patch is the shell. I see 2 other white patches in front of that one. They all might be something else.

The next time I see one of these tiny slugs I will try to photograph it from the side to see where the pneumostome is.

Katie said...

Nice post! It looks like you have a really great camera lens! I will be getting my own macro lens soon. Hope to be taking nice pictures with it and posting on my blog.

B Girardot said...

Thank goodness he lived, from the post title, I thought something bad happened at the end :)

gene pitts said...

Wow! Thank you, Mr. Orstan, for posting this photo. About two months ago, I found a slug very much like this on my right hand after being in my backyard garden for several hours. I live in Montclair, NJ. I would like to know more about slugs in general and especially about this species. Help, please.