Snail predation by Rove beetles?

[Jason Green]

I've seen old shells with holes as well...

I would think the holes are caused by song thrushes picking them up in their bills, as they pick them up and drop them to get to the snail inside.

How old are the shells? Perhaps they've been damaged, natural wear and tear once the snails died, perhaps an unlikely lack of calcium in their diet?

[haematocephalus]

Lots of interesting stuff on this thread .

Found the following via Google Scholar:
http://psyche.entclub.org/82/82-292.html

which is based on observations of captive beetles in America, with the Devil's Coach-horse (Ocypus olens) larvae and adults preying on the garden snail (Helix aspersa).

Doesn't go into a lot of detail about the feeding habits but includes:
"Generally, the shells were left intact. However, some of the smaller shells showed various degrees of destruction from the body whorl to the apex. Attack by an adult beetle resulted in more severe mutilation of the shell."

Martin


Martin Harvey

[Happibun]

Jason, the holes are in both newish and old shells, so I don't think that it is due to weathering.

There is a remarkable consistency to the size and shape of the holes. That more than anything else makes me think that birds and rodents are not the culprits. The holes are at most around 3 - 4 mm across, and no more. Most of them are roundish, although one shell has 2 holes, one round and one thin and long which may have been due to a failed attempt to breach the shell. If I get a chance I will find a lot of them and line them up for more photographs. I have no shortage of specimens!

In the mean time, there is a lot to look at and some reading to get to grips with. Thanks for digging out that article in Psyche Martin. In my google search I found a lot of links to articles that I could not open because I did not subscribe to the journals, the rest were tantalising parts of synopses and so forth, but no pictures to compare with and make a positive ID.

If it is a rove beetle making the holes, I presume that it would be with it's powerful mandibles, just biting through the shell. That would explain why the holes are not perfectly round. Marine shell boring gastropods dissolve their way through using dilute acids, and that is why they are so uniform and round. Anyhow, there's a good photo of Ocypus olens showing off it's formidable jaws in a defence pose in the Wikipedia article here - Devil's coach horse beetle - Wikipedia, the free encyclopedia . Frustratingly the article says nothing about snails... Natch

Please keep your ideas coming

Jo

[Kayleigh]

Originally Posted by Happibun

Jason, the holes are in both newish and old shells, so I don't think that it is due to weathering.

There is a remarkable consistency to the size and shape of the holes. That more than anything else makes me think that birds and rodents are not the culprits. The holes are at most around 3 - 4 mm across, and no more. Most of them are roundish, although one shell has 2 holes, one round and one thin and long which may have been due to a failed attempt to breach the shell. If I get a chance I will find a lot of them and line them up for more photographs. I have no shortage of specimens!

In the mean time, there is a lot to look at and some reading to get to grips with. Thanks for digging out that article in Psyche Martin. In my google search I found a lot of links to articles that I could not open because I did not subscribe to the journals, the rest were tantalising parts of synopses and so forth, but no pictures to compare with and make a positive ID.

If it is a rove beetle making the holes, I presume that it would be with it's powerful mandibles, just biting through the shell. That would explain why the holes are not perfectly round. Marine shell boring gastropods dissolve their way through using dilute acids, and that is why they are so uniform and round. Anyhow, there's a good photo of Ocypus olens showing off it's formidable jaws in a defence pose in the Wikipedia article here - Devil's coach horse beetle - Wikipedia, the free encyclopedia . Frustratingly the article says nothing about snails... Natch

Please keep your ideas coming

Jo

Whatever is causing it.. I want some to protect my hosters.

[hsl]

I'll be very interested to here the answer to this one. I came across a pile of empty snail shells whilst gardening once and wondered what was responsible.

Those beetle's have strong jaws but they couldn't bite through a snails shell IMO. It's hard for birds to Pierce the shells isn't it? Could it be a very small bird with a very sharp beak?

[Meta menardi]

I went out today to a few places where I know that there are large numbers of shells in the hedges, and I can't find any with holes as neat and consistent as that. Many of the old shells have all sorts of holes in them, but that is not the same thing.

I feel sure that I have seen reference to something similar somewhere, I shall keep picking away in my mind.

Of course it could be one of those things that no-one has ever really noticed before, or thought that someone else would know about. That is not as uncommon as it first appears to be, there were only so many Victorian vicars.

[Paul mabbott]

Yes, another option is that these holes were made post mortem. So it would be interesting to know whether these were old (i.e. well dead) shells. Small birds, especially blue tits, eat snail shells to maintain their body calcium levels; for small birds might not the apex of the shell be the place to attack? However, this occurs mainly during/after egg-laying.

Clearly what's needed here is a serious study - everyone examine the snails in their gardens, the empty shells, the number of shells that are damaged, where/how the shells are damaged, what time of year the damage appears ... easy!

Originally Posted by hsl

Those beetle's have strong jaws but they couldn't bite through a snails shell IMO. It's hard for birds to Pierce the shells isn't it? Could it be a very small bird with a very sharp beak?

[Kayleigh]

Originally Posted by Paul mabbott

Yes, another option is that these holes were made post mortem. So it would be interesting to know whether these were old (i.e. well dead) shells. Small birds, especially blue tits, eat snail shells to maintain their body calcium levels; for small birds might not the apex of the shell be the place to attack? However, this occurs mainly during/after egg-laying.

Clearly what's needed here is a serious study - everyone examine the snails in their gardens, the empty shells, the number of shells that are damaged, where/how the shells are damaged, what time of year the damage appears ... easy!

I never seem to find any snails dead..The only ones I see are eating my hosta's at night in the summer..

[Paul mabbott]

Originally Posted by Kayleigh

I never seem to find any snails dead..The only ones I see are eating my hosta's at night in the summer..

I thought people only planted hostas to maintain a good mollusc population.

We long gave up attempting to grow hostas, I've never really missed them, but what is so attractive about them to slugs/snails?

[Kayleigh]

Originally Posted by Paul mabbott

I thought people only planted hostas to maintain a good mollusc population.

We long gave up attempting to grow hostas, I've never really missed them, but what is so attractive about them to slugs/snails?

They must taste wonderful..I love hosta's, not to eat of course.