Retraction, Possible Cause

[Paul]

I've had 2 Cepaea snails die today from the tank with the tiny worms. When I say tiny, I mean, microscopic, they're hard to see even at 20x.

I thought they were related to the other worms because they look the same but now I'm not so sure. Looking around on the net about nematode worms it struck me that these may be the cause of all our woes. I have been inspecting the other snails in that tank, most have a few. I keep bathing them. Some seem ok and are feeding, others aren't but they all retract given time and some are losing weight. Most of them are still eating though although a few are refusing to come out.

You may have heard of types of nematodes used to kill snails and slugs. They crawl past the mantle into the shell and by some exotic relationship with various pseudomonas bacteria they cause the snails/slugs to stop eating and eventually die. Then the nematodes feed on the decaying snail and it all starts again.

Judging by the reaction of the snails I have found them on, I'm beginning to think these worms aren't there by chance, from coming into contact with the snails. I can't find many in the soil and boy have I tried.

It occurred to me that it is possible I have inherited some of these nematodes, through food, possibly organic. Washing the food isn't gonna get them all off and I'm wondering if these types of biological controls are being used more and more, this may be the cause, or one of the causes of the retraction problem.

I'm not even sure how to get a sample ready for the pest inspectors. I can take the bigger worms, as I have saved some but how the hell do I get the smaller ones into a tub. I'll have to see if they will take one of the seriously affected snails.

The only saving grace is that these worms seem to be able to swim freely in the snails' mucus, so I am wondering why they appear on the body at all. You'd think they would dive past the mantle as soon as they got the chance, but I'm not ruling it out in light of these deaths. Also, so far the cases I have seen are small snails and size could well be a factor. And it doesn't quite add up that after all this time, they haven't all been affected.

Anyway, I was hoping someone with the retraction problem who has a strong magnifying glass could inspect their snails for me, to see if they can find these things. If anyone can, this may shed some light on the problem.

SEARCHdeep_retraction

[Paul]

Just to add, that the commerically available ones that are used quite alot, apparently kill a slug in under 21 days. Now that is for native species, who knows what affect they would have on larger snails like Achatinids. As I said, apparently size is a factor. But I'm thinking even if they don't kill the snail, it could be enough to make them ill for long periods of time.

[Deleted]

it sounds a good theory, ill have a look at a retracted snail of mine.

[copigeon]

Paul. I'd hope your theory was right to give us some idea why this happens. However.

I had 24 juvenile fulica a month ago. Had been fine for the past 2 months, growing well. 20 were from an ebay seller, which I was raising for a school project. The other 4 I had a longer while back from one of the guys on this forum.

Pretty much suddenly, no change of substrate or otherwise. I started to experience the same retraction problem with these snails. No real reason for it it seemed, but depsite best efforts every single one of the 20 died. And 4 survived completely unbothered by the whole affair.
I cannot confirm that the 4 were the 4 I had recieved from this forum as they were all about the same size and mixed together. But it seems terribly coincidental to me that 4 should live and 20 die.

So I wonder if it is a viral thing which some snails, genetically have a resistance to?

The other reason Im not so sure its a pest issue, is because the remaining 4 I moved straight in with an adult, a perhaps daring experiment. But the adult has had no ill effect. And all 4 are now in with the rest of my Fulica culture.
Should they be carriers of a pest I'd hope to see some effect on these snails too? Theres enough in there from different sources that not everyone could be resistant to it surely?

[KathyM]

Justin has been in with the others from the beginning - moving him out made him worse. The others have shown no signs whatsoever of illness, including Jethro who was as small as Justin when he arrived. The others are the picture of health.

Very interesting indeed, but I don't think it's what's causing Justin's problems. What strength magnifier are you using? Baz is partially sighted and might have one kicking around for me to check.

[Paul]

I'm using a 20x jewellers magnifying glass. Cost me £4 on ebay including postage.

It sounds unlikely in your case, and I'm not even sure these are actually pest worms yet. But it's a possibility worth eliminating for anyone with retraction problems because the symptoms sounds similar.

[Val]

Paul, sorry if I have missed something here, but where exactly do you think these worms have come from?? I know you mentioned organic food, do you mean organic food like from Tesco's?

Val

[Paul]

From anywhere really, I buy mine from both the supermarket and market stalls. I can't think of any other way they could get into my tank, except on another snail but judging by the snails reaction I would have thought it would show itself sooner. I don't use moss and my substrate was compressed coir blocks. I've not had any problems since my last retraction case months ago. And I keep each tank strictly separate as a precaution. These worms can survive dessicated and rehydrated, a 70% survival rate within 24 hours so they must be pretty hardy. I do wash everything thoroughly and I do an indoor job, so it's not like I've had dirty hands and then dealt with the tanks.

Still not sure if they're just juvenile harmless worms that have got stuck on the snails or if they really are harmful ones. I've moved my native species to a colder room and they have been much more active, plus that should limit the potential of the worms further. But that doesn't explain the reaction of the tropical ones.

[Beth]

I had always been under the impression from reading organic gardening articles that nematodes were only effective against small slug species (such as 'keel slugs'), but that's not to say they wouldn't effect larger slugs and snails. As for introducing them into your tanks I would think that would be easy as they are naturally present in the soil and yes you are more likely to get them on organic food as they are added to the soil by organic growers as a natural slug control.

Manufacturers say that the nematodes effect slugs ups to 8cm which surprises and worries me. It seems that the death of the snail/slug is when the nematodes spread which could explain why other snails are not effected until later or never as people often separate ill snails. Nematodes seem to work better on slugs that hide in the soil so snails that burrow are at more risk.

>>Once the slug dies nematodes spread out over the cadaver and feed. When the food source is depleted, the nematodes form new juveniles to leave the cadaver in search of new slug hosts (Tan and Grewal, 2001).<<

So maybe as a precaution any snail that has this retraction problem is best isolated. I don't think all retraction problems are caused by these nematodes but it is possible that some are.

I'll get a magnifying glass out later and have a look at my retracted snail....will update if I find anything.

I feel this whole subject is definitely worth further research, because as Paul says who knows how these nematodes would effect larger non native snails in warm tanks...

oh for more hours in a day!

Beth

[Beth]

Just found this interesting article...


www.bbc.co.uk/nature/animals/features/291feature4.shtml


>>>Their more recent work suggests that the nematode worm itself does not kill molluscs but the bacterium that it carries - Moraxella osloensis - does<<<

I haven't got time now .....but a quick search brought up lots of interesting reading on Moraxella osloensis.

Could this bacteria be our problem

Beth

[Paul]

Looked into that bacteria more and this could be promising:

"Effect of antibiotics on the pathogenicity of M. osloensis to D. reticulatum Penicillin can interfere with the formation of cell walls of bacteria, while streptomycin can block the synthesis of bacterial proteins. The two antibiotics were used to inhibit the growth and metabolism of M. osloensis, thus testing their effect on the pathogenicity of the bacterium to D. reticulatum. A bacterial suspension (1.23 × 1010 CFU/ml) from the 60-h culture was prepared as described above. Fifty microliters of the suspension was injected into the shell cavity of each slug with or without penicillin (500 U/ml) and streptomycin (500 µg/ml). Twenty-four slugs were maintained for each treatment and were then separated into three petri dishes (eight slugs per dish) as three replicates for the calculation of slug mortality. At the same time, slugs injected with the antibiotics or the saline solution served as controls. All slugs were fed pieces of fresh carrots and cabbage leaves and incubated at 18°C. The numbers of dead slugs were recorded every day for 12 days."

It looks like molluscs may be treatable with antibiotics.

[Deleted]

so we put penicillin into their breathing hole?

[Paul]

The bacteria will be formed behind the mantle, but getting the antibiotics into the bloodstream should tackle it. How you get into into them without injection if they aren't eating is beyond me though.

[Beth]

Wow Paul, do you think we could really be on to something here? This was the direction I was hoping further research would go.....this is really exciting (I'm keeping my fingers crossed)

Wouldn't it be great if treatment was as simple as giving them warm baths with dissolved antibiotic in (it would be important that the correct antibiotic was used though) My vet helped me treat a wild frog once with a crushed leg using just this method, the frog absorbed the antibiotic through his skin and made a full recovery from what was an horrendous wound and I was able to release him after several weeks

Beth

[Paul]

It may work, I still can't find what size particles can pass through the skin membrane. It's definitely worth a try though if you have any antibiotics handy. Certainly nothing to lose when you look at the recovery record.

[Arno]

That sounds really promising.I'm sure it would work the same way with snails as that frog.Since snails can dissolve cuttlefish with their foot and take it in that way,they wouldn't have any problem with an antibiotic.

[Val]

Paul, if what you are saying is correct and that washing organic food does not remove all of these nematodes then it stands to reason that we are eating them also!! I am also wondering if non organic would be less of a risk to the snails than organic.

Val

[Paul]

They are safe to us apparently. Also, it is likely that eggs, not live worms are to blame.

[Deleted]

but how do we know antibiotics won't do more harm to the snails than good?

[Paul]

"At the same time, slugs injected with the antibiotics or the saline solution served as controls."

If they were controls they must have survived the bacterial infection more than the one's without. Over use of anything may be detrimental but a short treatment to overcome something could work and may actually save their lives. In a case like that, it's worth a go I think.

[Deleted]

are you going to try it Paul?