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Slug or Nematode?

 
Maura wrote:-
>I am wondering what these predaceous nematodes look like.
>I have been trying for a year to identify a new creature in my >garden,
and I don't know if it is a slug, nematode, or what!
>It is from 1/2 to 1 inch long, very black, skinny  -hard to tell >which
is the beginning and end, one end is pointed and the other >end is
flat...I find it on slugs, and also mostly decaying >vegetation. I have
searched books in several libraries, and feel >very frustrated that either
there aren't that many good ones >(with pictures) on slugs,
worms,nematodes, etc or I am just not >finding them! any info on this
would be greatly appreciated. BTW, >I also wonder if this was introduced
into my garden from some >horse manure I added to my compost....thanks,
Maura
    
Hi Maura,

>From your description, I'd say it was some sort of terrestrial flatworm. I
presume you are in the states, and I think I'm right in saying there are
several species over there. most flatworms are aquatic, and even
terrestrial ones can only live in very damp conditions. As their name
suggests, they are very flat and ribbon-like, and move with a gliding
motion without muscular effort (they have cilia on their underside). All
flatworms are predatory, and terrestrial ones generally produce lots of
mucus to help keep moist. They probably eat earthworms, slugs etc - some
have recently been accidentally introduced to Britain from new Zealand,
and there is a lot of concern about the damage they are doing to native
earthworm populations.

Nematodes, on the other hand, are round in cross-section (hence the common
name of 'roundworms') and move with a thrashing motion. You are unlikely
to see one though, since most of them are microscopic, and those that
aren't are gut parasites. They are a very successful group, and include
free-living scavengers and parasites of animals and plants. There is even
(reputedly) one which lives in Bavarian beermats!

Finally, it is just possible that your black thing could be a terrestrial
leech or a strange species of slug. Leeches can be distinguished by their
segmented body and the presence of a sucker at either end (though these
are not always obvious). Don't automatically assume that leeches are pests
- many of them feed on snails and other invertebrates, which sounds a bit
like your description. Slugs (like nematodes and flatworms) are
unsegmented, but they are always rounder that a flatworm. Some slugs are
quite elongated and burrow, and this could be what you saw. To be quite
honest, your best bet is to have a look at one of your creatures with the
aid of a low-powered microscope or a hand lens and a good invertebrates
text book (I like Invertebrates by Brusca and Brusca, published by
Sinauer)

Hope this helps,

Tristan
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