A snail safari

It was drizzling when I left home for work, a perfect day to look for some active snails for 30 Days Wild day 2 (always look at the bright side of life!). I hadn't walked long when I spotted some Strawberry Snails, Trochulus striolatus on the stones lining a front garden, probably feeding on algae encrusting the stones. A little while ahead a Garden Snail, Cornu aspersum, also in a front garden, probably searching for something more substantial.  I popped into Pearson Park Wildlife Garden. It is hard to visit it without finding a Kentish snail, Monacha cantiana, which love to walk on the paths. I found one climbing on grass (top shot). Many Kentish snails or all sizes were active on a wet trunk by the path, amongst them a White-Lipped snail, Cepaea hortensis.
 At lunchtime, I popped out a wooded area on campus and rooted around in the undergrowth and inspected the underside of pieces of wood and rocks. My first find was a Draparnaud snail, Oxychilus draparnaudi under a very rotten tree branch. Later, inside a plastic pot (part of an insect hotel) I discovered a Girdled Snail, Hygromia cinctella, which was nice as it is a first record for this area.
 Once home I knew where to find a tiny snail: in my log pile. After finding many garden snails dormant in amongst the logs, I spied a small group of Common Chrysalis Snail, Lauria cylindracea, and the best thing is that they were also active!
 Today's total then of seven species of snails found in not much time. At least two other species are quite common within walking distance of home: the Brown Lipped snail, Cepaea nemoralis, the Garlic Snail, Oxychilus alliarius, and the Rotund disk, Discus rotundatus.

Strawberry Snails, Trochulus striolatus

Garden snail, Cornu aspersum 

White lipped snail, Cepaea hortensis.

Draparnaud snail, Oxychilus draparnaudi

Girdled Snail, Hygromia cinctella

The Common Chrysalis snail, Lauria cylindracea

If you like snails and would like to learn to identify them I recommend these two publications, a folded up laminated An Illustrated Guide to the Land Snails of the British Isles, and the 2nd ed. Land Snails in the British Isles (with identification keys and drawings), and of course follow James Morris-Harding's quest to see all British land snails in 2015 the Snail Trail, either on Twitter (@UKSnailTrail) or on his blog.
 And if you identify them, why not send your records to iRecord?

Supercool snails

In the last couple of months, I've regularly come across active Girdled Snails on my way to work. Damp, but often very cold even during frosty mornings I see these small snails on they way back to their day retreats on the pavement by a front garden, presumably after having been active, feeding? during the night (above, on the 23rd of January at 8:48 am). This nonchalant cold hardiness is in stark contrast to common or garden snails (Cornu aspersum), which have been dormant for a good while, and won't become active until March or April. Why is that? how cold resistant are snails? do they differ in their cold hardiness?
  Land snails are a very useful indicator species for ancient environments, as their shells fossilise very well and can be often identified to species level. Despite this, surprisingly little is known on their cold tolerance. Amazingly, 35 snail species live north of the arctic circle and 44 species over 2,000 m of altitude. How do they survive ice-cold temperatures? As other invertebrates unable to migrate snails have two strategies to survive sub-zero temperatures: freezing avoidance and freezing tolerance. Species that engage in freezing avoidance can actually be active in sub-zero conditions by supercooling. A supercooled snail will be at a temperature under 0 oC, but it won't be frozen, that is cool indeed! They can do this by producing large amounts of small sugar molecules that bind water and make their tissues more dehydrated, and also large antifreeze proteins, which inhibit ice formation even further, allowing them to remain active at sub-zero temperatures. Smaller snails (of shells up to 15 mm) appear to be more freeze avoidant than tolerant, and therefore, they are better at supercooling.

A favourite overwintering spot, with dozens of garden snails of various sizes under a tile lined against a wall in my garden.

We know a bit more about the cold tolerance of garden snails, thanks to the research of Armelle Ansart, from Rennes University and her colleagues. The garden snail has limited supercooling abilities, it is a partial frost tolerant species (they can only survive to a minimum of -5 oC). The are partially freeze-tolerant, avoiding freezing by emptying their guts - gut contents can start the formation of deadly ice crystals, reducing the water content of their body (which makes soluble chemicals more concentrated and decreases the temperature at which ice crystals form) and producing an epiphragm, a hard, thick calcareous layer of mucus that seals their shells shut, keeping the deadly moisture out. As an aside, the epiphragm is also produced in very dry weather, during aestivation, another dormant state in snails, but then the epiphragm keeps the moisture in.

An early waking young garden snail (28 Feb 2011), still carrying its epiphragm attached to its shell.

The preparation for overwintering seems to be kickstarted by the decreasing photoperiod of autumn, rather than temperatures dropping. Garden snails also seek high and dry microhabitats to overwinter and congregate, sometimes in very large numbers in favourable spots, such as the underside of logs, stones or holes in tree trunks. Large garden snails are more resistant to the cold than small ones, as they are better at avoiding the formation of ice crystals, so adults are more likely to survive a hard winter than immature snails.
 As for the Girdled snail, sadly I found nothing, although a comparative analysis of cold hardiness by Ansart and colleagues found out that its congeneric species Hygromia limbata freezes at -7 oC, not too impressive when compared to the tiny Columella edentula, also a British species, which doesn't freeze until the temperature descends to -17 oC, but probably enough to allow it to survive in the mild frosts of Hull.

References
Armelle Ansart, Annie Guiller, Olivier Moine, Marie-Claire Martin, Luc Madec. 2014. Is cold hardiness size-constrained? A comparative approach in land snails. Evolutionary Ecology, 28: 471-493. Here.

Ansart, Armelle, and Philippe Vernon (2003) Cold hardiness in molluscs. Acta Oecologica 24.2: 95-102.

Ansart, A. & Vernon, P. (2004). Cold hardiness abilities vary with the size of the land snail Cornu aspersum. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 139: 205-211.

Strawberry Snail and Girdled Snail

Continuing today with the snail theme due to the wet weather. My 5 yr old daughter has a keen eye for little bugs, and today, all on her own found these two snails on a front garden in my street. Two species that we haven't found in our garden.

This is the Strawberry Snail, Trichia striolata a relatively small snail (about 10 mm wide), with a dull, finely sculptured round shell and dark body. The shell colour is variable, but this is the most common in my area. The shell has got an 'umbilicum' underneath, an open space between the shell worls. It genus name refers to the fact that the snail is hairy when young.

This is a similarly sized snail, the Girdled Snail. This angle shows the white keel that makes them easy to recognise. I have written about them before.

The courtship of garden snails

While having a cup of coffee in the conservatory during breakfast, I noticed a pair of snails, one of them with its genital pore a bit everted. Aroused snails! It was 10:09. I quickly finished my coffee and came closer. Despite coming across tens (hundreds?) of slumbering mating snails for years, I had never witnessed the actual preliminaries of it, which was now taking place just behind the conservatory glass, on its wooden frame. The series of events was fascinating, by its slow, but surely developing tempo, its tactile nature, its synchrony, and the dance-like quality of it. First the snails approached each other, with their heads up, appearing to avoid exposing their gonopore (an opening behind the right hand side of their heads from which their penises emerge and where their vaginas open) to their partner, while at the same time touching each other's gonopores with their mouths in long, slimy kisses, and tentacles touching, occasionally retracting their heads. One of the snails appeared more keen, while the other regularly turned round and then back, each time coming closer to its partner.
Then courtship became more intense, both snails everting their penises and aligned their bodies toward each other, exposing their right sides to each other. Finally, after a couple of hours, they were sleeping in their copulating embrace, and their eyes retracted. I missed the darting and I couldn't see any protruding darts. Here is a slide show.

Every now and then, I checked on the snails. They slept on the frame of the conservatory most of the day (at 16:45 they were still mating). I just checked (21:40), and only one remains. The duration of mating in this species is about 7 hours.
I have uploaded a video with an early and a later sequecing of the courtship.

No matter how long you've been acquainted with a particular species, there is always something surprising and wonderful you might still witness.

Rotund disk snails

In a walk to my local cemetery I found this group of disk snails, Discus rotundatus, under a decaying branch. They are small snails up to 7 mm in diameter, with a lovely ribbed shell with reddish banding. It feeds on algae, fungi and decaying vegetation in damp and shady places and shelters in groups under bricks, rocks, logs and at the base of tree trunks in dry weather.

Garden Snail Parade

Since I started this blog, I have been surprised by the diversity of land snails about in the city. As I have managed to get most of them on white background, I decided to write a post and display them all together.

Moss snail, Lauria cylindracea, a tiny, easily overlooked species which gives birth to live offspring. 

Garden Snails, Helix aspersa (=Cantareus aspersus), unashamedly mate in the middle of your garden  path throwing darts at each other. 

Girdled Snails, Hygromia cinctella, like walls. An introduced species since 1950, still expanding across Europe from the Mediterranean.

Kentish snail, Monacha cantiana prefers drier places. This species, introduced in the UK during Roman times, is a very common snail in my local Wildlife Garden. They can be darker with pale speckling.

Glass Snails, Oxychilus draparnaudi, are carnivorous snails that have caused havoc on native snails when introduced outside the UK.

Amber Snails, Succinea putris usually live in very damp places, but can be also found away from water. They cannot completely retract their bodies inside their shells.

Brown Lipped Snails, Cepaea nemoralis are very polymorphic in colour and pattern.You might be lucky to have these beauties in the garden.  

Have you noticed all the snails are facing to the right? This is because most (90%) of all snail species have right-handed shells (dextral). Occasionally a left-handed individuals appear in populations of right handed snails. These face a problem when trying to mate, as the genital opening will face away from most other snails in the population. The genetics of shell handedness has been elucidated in some species and appears to be determined by mutations in a single gene, but the left-handedness trait is expressed not in the mutant, but in the resulting offspring.

More information

Visit the Molluscs posts in Bugblog.

Terrestrial Mollusc Tool. A wonderful resource for US molluscs. Contains also lots of info on introduced European slugs and snails.

Another girdled snail

I spotted this Girdled Snail, Hygromia cinctella, the second ever I have seen, climbing up a wall in my street a couple of days ago. The white whashed wall made a white background for it and I was pleased to get to photograph the live snail as it went about its business.