18 April 2006

Mmm…worms

Last week I wrote about how my son and I had chanced upon slugs eating a dead earthworm in our backyard. The following nite we decided to reproduce our observations by actually offering earthworms to slugs. During the afternoon we went out and collected dead earthworms from the sidewalks—casualties left from the morning’s rain. A brief soak in a solution of trisodium phosphate, followed by a water rinse, restored, not their lives, but their plumpness.

Later in the backyard around 9 pm, the first slug we saw was a large Arion subfuscus. I placed one intact “reconstituted” worm a few centimeters in front of it. A minute later, the slug had already contacted the worm and was starting to eat it.


Soon the slug had literally chopped the worm into smaller pieces and was consuming each one slowly.


I don’t know how often these slugs get a chance to eat dead earthworms and other animal matter in the wild. But I have just thought of a way this question can be answered easily. In a previous post, I mentioned how I had determined the diet of the land snail Oxyloma retusa from the microscopic examinations of its feces. The feces of slugs should also reveal what they normally eat. Earthworm flesh, once it has gone thru a slug’s stomach and intestine, would probably be difficult to identify. But, I am almost certain that the tiny hairs (setae) that cover an earthworm's outer skin will survive intact slugs’ digestive processes and can be identified in their feces.

That will be the next weekend’s project.

34 comments:

ravyn isabel said...

woah very interesting. i like the photos, very sharp.

Megan Paustian said...

Wow, those Arion subfuscus are ravenous. I'm surprised how well slugs can eat earthworms, since they just have little raspy teeth.

Pamela said...

Fascinating! Great pictures, and a surprisingly beautiful slug.

T. Beth said...

What strange and amazing photos! I didn't know that a slug would do such a thing... Or that earthworms had hairs!

pascal said...

"Nobody likes me, everybody hates me... guess I'll go eat worms."

Nuthatch said...

ugh. I just ate sushi...

James Watson said...

Tonight after two days of on and off rain many snails were out eating the wet leaves in my backyard in Brighton, MA (A suburb of Boston). I accidently stepped on the same large garden snail I first noticed after telling myself to try to avoid the little critters. I felt bad since it was just sitting there for at least 30 minutes just chomping away at the leaves. Anyways all of its organs and fun gooey bits were exposed and when I came down about an hour later a large slug was eating the remains. I also noticed that nearby snails were seemingly avoiding the large slug. I was just wondering do some slugs prey upon live snails too or was it just out for the dead one? Also how are the slugs/snails able to find their food so fast?

AYDIN ÖRSTAN said...

James,
As far as I know there are no strictly carnivorous slugs in the northeast U.S. The slugs in the European genus Daudebardia are carnivorous, but they may feed on earthworms.

There are, however, many carnivorous snails that feed on other snails. One such snail is Haplotrema concavum, a common snail of northeast U.S. forests.

Snails & slugs have a good sense of smell.

Jennifer said...

Picture of a Spanish slug eating an earthworm, spotted this evening on a stroll thru the neighborhood.

eped said...

wonderful! that photo of the first kiss, with the flowers (lilacs?) is especially nice.

AYDIN ÖRSTAN said...

Phlox, not lilacs.

Anonymous said...

This spring and summer we have expereinced a significant amount of slugs and an absences of earth worms.

Anonymous said...

Hello. Me and my housemates were wondering if slugs would also eat other dead slugs as well as earth worms since we have a bit of a slug problem in our house but the dead slugs disappear! Any ideas?

AYDIN ÖRSTAN said...

Dead slugs decompose very quickly unless they dry out. They may also get eaten by ants, isopods, etc.

I don't know if slugs eat dead slugs. They may.

Jackie said...

Now, I really don't get why anyone would care if and what a slug would eat, I only know, I find them to be Nasty little creatures, and get rid of as many as I can find.

AYDIN ÖRSTAN said...

Jackie: Every creature on earth is a product of millions of years of evolution. By learning from them their secrets, we get to understand our own evolutionary history. By killing them pointlessly, on the other hand, we couldn't go very far.

Leslie Ann said...

A workman stepped on a slug early this evening on my front stoop. I just went out there to sit and there is a large slug eating it. So it seems that slugs do eat dead slugs.

AYDIN ÖRSTAN said...

Leslie Ann: thanks for further confirmation of my observations.

WoodvilleSeedsaver said...

I have been wondering about the interaction between slugs & snails for ages. They are treated & often described as basically the same thing, but I suspect slugs - being very polyphyletic - are prone to being victims of generalisation. Most snails are more related to slugs than most slugs are to each other. Particularly, scavenging, compost-eating slugs are related to snails, whereas carniverous slugs are not really related at all. They just look similar & all got named slugs, so far as I understand things. There are slugs that hunt snails & cut a window in the shell with its single tooth, before sucking it out. I have seen shows on them & watched them do it in my garden. Carniverous slugs move relatively fast compared to snails & run them down in a slow-motion kind of way. Not much different than any predator & its prey really. In Australia, there is a native snail that is related to carniverous slugs & also hunts snails.
But in normal terms, ppl think of slugs & snails similarly as in slug & snail poisons. I don't use any kind of pesticide for fear of killing carniverous slugs or native snails. They are too fascinating to kill for the sake of protecting a lettuce or something.

AYDIN ÖRSTAN said...

All slugs must have evolved from snails, because, as far as I know, there are no extant slugs that inhabit intertidal, brackish water, mangrove, rocky or beach habitats, that is, the places where the ancestors of all the terrrestrial gastropods must have lived.

Anonymous said...

Hi Aydin,

The only intertidal slugs I know of are the Onchidella species, marine pulmonate slugs which live on rocky shores.

Susan J. Hewitt, NYC

AYDIN ÖRSTAN said...

Susan, thanks for the correction.

Anonymous said...

You are very welcome Aydin, I always enjoy your blog very much! Actually I like all of the topics you write on, molluscan and otherwise.

For anyone who is interested in seeing some pics of intertidal marine pulmonate slugs, there is a lot of very good info on Onchidella and all the other other genera in that same unusual family at Bill Rudman's fine site, the Sea Slug Forum, for example at: http://www.seaslugforum.net/factsheet.cfm?base=onchid

best to you, and Happy New Year 2008,

Susan J. Hewitt, NYC

Susa said...

How wonderful to find your site! My 3-year old son and I were looking for bugs this evening and happened upon small slug that appeared to be chomping on a dead earthworm. (We live in southern California and the slugs here seem to be much smaller than those I have seen in the Northeast or Pacific Northwest.) A moment later, however, the slug decided to leave, and the worm seemed to be intact. We weren't sure if the slug was actually interested in eating the worm (I didn't realize there were carnivorous slugs), but your website confirms that it can happen. Fascinating.

Anja said...

This is absolutely fascinating.I had no clue there were hunters and carnivores among the slugs and snails population. I will so have to read up on this. Thanks for posting. (Your pictures are amazing)

Christopher said...

You have a wonderful and intresting blog!! I just thought I'd let you know slugs eat people. check this out SLUGS EAT PEOPLE

Anonymous said...

hi, my name is Daniel...the past few nights i've been seeing these slugs all around the yard, well it rained a couple of days , so i guess it was normal,but the weird thing i saw was, there were like scraps of meat by the garbage bins, i guess it fell from the bag or something, an those slugs were all over it, eating away...i was like is this normal or what....

School for Us said...

Great photos! I saw a slug eating a worm in our backyard last night and thought that was unusual. I looked it up and several sites just talked about slugs eating plants, etc, so it was nice to come across someone else verifying that slugs do eat worms sometimes!

Anonymous said...

Have just come across two slugs eating either end of a dead worm. Interestingly, both had the same indentation on the right side of their head as seen in the photo above. Wonder what that's all about?

Anonymous said...

That "indentation" is their respiratory opening, their pneumostome, it leads into their mantle cavity. That's how they breathe. Sometimes it is open to let air in and sometimes it is closed. When it is closed you can't even really make out where it would be until it opens again. If you didn't know much about them, you might expect a land slug like this to be symmetrical, maybe because it looks a little worm-like, but their internal anatomy is not symmetrical, and their "lung" opens on one side like that.

Best,

Susan J. Hewitt

Wormcity said...

Fabulous pictures - thanks for sharing

Warwick said...

Slugs definitely eat dead slugs. My preferred method of culling the critturs in our garden is to go round and stamp on them as they march from the bed across the lawn. I go back 30 mins later and each body is being devoured by 3-10 other slugs. So I get them as well. They also love dog food, which upsets our dog as his food isplaced outside and he has to race to get it before the slugs do. Interestingly not many snails go for the dog food or the dead slugs.
WF England

Anonymous said...

After a 1.5 week drought here in middle engand, we had a much needed day of rain, since weve been experiencing trouble with snails eating all our newly planted seedlings I decided i'd better go and do a check, well there were dozens... and interestingly I saw 2 snails attacking a still live giant red earthworm. Interesting!

Anonymous said...

I have slugs eating ants off a jelly baby my daughter dropped in the garden any ideas why