Macro Monday: Cantareus apertus

A lucky encounter with a juvenile Cantareus apertus, also known as the green snail. Native of the Mediterranean and North Africa, these snails spend most of their life underground, but emerge after rain. Subadults like this one have a yellowish-green shell and body, which will darken with time: as adults they are almost black fleshed and have uniformely brown shells.

In spite of their small size (about 2,5-3 cm in diameter), these snails are highly prized for culinary purposes, especially in southern Italian peninsula of Salento, where they are known as municeddhi, municedde or moniceddi. (They are said to be far superior to other edible snails, even Helix pomatia)

 

 

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Little crawlers grow up

Six-week old Cornu aspersum (a.k.a Cantareus aspersus or Helix aspersa), the common garden snail. Born transparent, they began developping shell pigmentation after a couple of weeks, starting with the bands. The final pattern of their shells however won’t be certain until they have fully grown: until then the bands continue evolving as the shell grows and may become thicker or thinner, darker or lighter, and adjacent bands may merge into a single, broader one while others may simply fade and disappear. As such, even if apparently all juveniles developped five bands at first, adults may have less.

Their bodies are still light coloured: body pigmentation will take a few months to become apparent, starting with their head and dorsal stripe.

Eaters of the dead

Crawling in a wood in broad daylight, two Arion slugs approach a lucky meal: a dead conspecific. Many snails and slugs are saprophagic, i.e. feed on decaying matter and dead animals. And some of them, like Arion slugs, won’t hesitate to eat dead snails or slugs of their own kind.

Cannibalism in some form or another is not infrequent among gastropods: several snails (including Pomacea bridgesii and other common aquarium snails) will feed on the remains of dead conspecifics, and sibling cannibalism has been observed among hatchlings (e.g. newborns of the common garden snail, Cornu aspersum, will sometimes eat the other eggs that haven’t hatched yet). Few species, however, hunt live individuals of their same species: Schizoglossa novoseelandica being an example. By contrast, despite being known as “cannibal snail”, Euglandina rosea (rosy wolfsnail) will rarely prey upon individuals of the same species.

GLOSSARY

Intraspecific predation: from Latin intra “within”, predation within the same species = cannibalism
Adelphophagy: from Ancient Greek ἀδελφός (adelphos) "brother" & φάγος (phagos) "eater" = sibling cannibalism

Literature:

• A predatory snail distinguishes between conspecific and heterospecific snails and trails based on chemical cues in slime
• First report of cannibalism in Triplofusus giganteus (Gastropoda: Fasciolariidae)
• Influence of egg cannibalism on growth, survival and feeding in hatchlings of the land snail Helix aspersa Müller (gastropoda, pulmonata, stylommatophora)
• Sibling Cannibalism in Juveniles of the Marine Gastropod Nassarius festivus (Powys, 1835)

Keeping snails as pets: how to set up a simple terrarium

You just found a little snail in your garden (or was it your salad, maybe?), and despite its slime and all, you actually think it’s a cute critter. So cute that the idea the resident gardener (spouse, parent, neighbour…) wouldn’t think twice about killing it makes you feel sorry for it and you decide to take it home for safety.

Whatever your reasons, congratulations, you have a pet snail! Now what?

Brought to you by popular demand, this post will share with you the basic tips and information for setting up a simple but effective terrarium for local snails

Mother & baby

Adult Cornu aspersum, carrying one of its newborns

Close-up

More pictures of the hatchlings.

The name’s Maximus, Limax maximus…

…and he’s coming for you!

Meet the leopard slug. This shell-less gastropod is notorious for its peculiar mating rituals (but I’ll fully cover this topic in a separate blog post) and owes its vernacular name to the attractive and highly variable patterns of black spots, blotches or stripes that adorn its body. But similarities don’t end here: like a leopard, this slug is an agile, swift and elegant hunter.

When not indulging in a snack of deliciously decaying matter or excrements, this slug is in fact a keen predator, who hunts other slugs, snails and their eggs… a benefit for all gardeners who, in return, are rarely aware of (and thankful for) this service.

Reportedly, these slugs sometimes engage in cannibalistic habits too, although I haven’t personally witnessed any aggressive behaviour between the two specimens I keep and which have so far cohabited quite peacefully.

Assume the defensive stance!

Retreat!

Night crawler: extremely shy by daylight, Limax maximus is almost exclusively a nocturnal creature – more so than Arion species, which I encounter in the wild at any time of the day. Limax maximus, by contrast, will usually spend daytime hiding in a cool, damp place which will only leave after sunset.

Like Arion and other slug species, Limax maximus will react to a threat (real or perceived) by contracting its body, but unlike Arion, leopard slugs seem faster to retreat as soon as a chance arises.

Despite its binomial name suggesting otherwise, leopard slugs are not the biggest slugs of the world – or even of their native Europe, for the matter. The biggest European representative it’s a close relative, Limax cinereoniger.

Life and romance of a one-eyed Roman snail

Or: Reproduction and Birth in Helix pomatia.

Blinded by love? Alezan the burgundy snail (Helix pomatia, a.k.a Roman snail) has only one eye. Whether this is the result of trauma or birth defect, it’s unclear, but one thing is certain: it hasn’t prevented Alezan from living a healthy, functional life – or successfully reproducing, for the matter.

Alezan and Margot, mating. Both adults (and fellow Helix pomatia Blanche, not shown)
were purchased from a snail farm in Austria

Mating in Helix pomatia occurs in a frontal, standing position: the two individuals face each other, their pedal soles in contact. As most land snails, Helix pomatia is an incomplete hermaphroditic species, with each individual having both male and female organs, but unable to self-fertilise.

Laying eggs

After mating, both adults will lay eggs, in a hole several centimetres deep in the ground, where earth is moist and soft. The eggs are fairly large (about 1cm in diametre). Egg laying is a strenuous activity, which may take up to a full day for a burgundy snail.

Alezan’s babies, leaving the nest: it may take the newborns a few days to leave the underground after hatching

Eggs were laid on September 14, and hatched after two weeks. In the wild hatchlings born so late in the year may not survive their first winter.

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Further reading:

• Helix pomatia: Mating and Reproduction (by Robert Nordsieck)
• Reproductive performance of Helix pomatia (Gastropoda: Pulmonata: Helicidae) and survival of its hatchlings under farm conditions (American Malacological Bulletin)

Guide to land snails of Andalusia, Spain – pdf (free download)

For those of you interested in Mediterranean and especially Iberian land snails, here is a gem: Caracoles Terrestres de Andalucía. General information, identification, distribution maps, and full colour photographs of the terrestrial gastropod species of southern Spain, available in this 300+ page book (in Spanish), fully downloadable for free as a pdf. (Courtesy of the official website of the Autonomous Community of Andalusia – Consejería de Medio Ambiente).

Rumina decollata: growth stages

The European and Mediterranean representative of the family Subulinidea (a relative of Achatinidae), Rumina decollata is a special snail in so many ways.

First of all, it is a voracious predator (although it will also feed on vegetables and decaying matter). Second, any other snail with a fractured shell apex would not, under most circumstances, survive. But to this disconcerting species, a broken shell is its trademark. And an inevitable part of its growth.

June 2010: Almost transparent in sunlight , a young Rumina decollata shows
the truncated shell its species owns its name to (decollata = de-tipped)

The same snail, in September 2010: none of its juvenile whorls are left

The decollate snail (Rumina decollata) is a common garden dweller in many parts of Europe, easily identified by its conic, light-brown-to-cream shell with slightly convex whorls, and, most of all, its truncated apex (tip).
In most terrestrial snails, growth is simply a process of addition: new whorls form around the columella and the shell size progressively increases. Rumina decollata however is a special exception to this: a juvenile may have about 8 whorls, but an adult just as few as 4. Where did the missing whorls go?

May 2010, juvenile Rumina decollata: note the shell tip still intact

The answer lies in the process of shell decollation (colloquially known as “de-tipping”), a progressive destruction or loss of early whorls that occurs along the growth of new ones. Beginning with the loss of the blunt tip of the intact, juvenile shell.

Tip loss in juvenile Rumina decollata

A calcareous seal: survival of the snail despite the apex loss is ensured thanks to a calcareous deposit that formed inside before the tip loss.
As the snail continues growing and new, much larger whorls form, changes occur in the old ones. The snail retreats in the new whorls, forms a new calcareous seal inside the shell and the old whorls, now fragile and empty, are chipped off.

Shell growth after tip loss (August 2010)

Decollation – inevitable? Some sources explain the tip loss in Rumina decollata as a consequence of grinding the adult shell against hard objects, but based on my observations in captivity, this is not the case.
Firstly, it does not occur in adulthood, but at an early stage of growth, as shown in the pictures. Secondly, while in the wild friction against rocks and hard surfaces may aid or accelerate the decollation process, the loss of old whorls for Rumina decollata is inevitable even in a trauma-free existence.

Adult shell: by now, all the early, juvenile whorls have been lost

To put at test the theory that decollation occurs simply as a consequence of friction, the specimen shown above – nicknamed Dedalus – was raised in soft-substratum terrarium and all precautions were taken to preserve its shell intact for as long as possible. In spite of that, old whorls progressively changed, appearing thinner and more fragile just before chipping off.
The impression I was given was that the snail was actually reabsorbing calcium from the old whorls (despite the extra calcium supplies available in the tank in the form of cuttlefish bones) before ridding of them.

Costly compromise? As far as my personal theory goes, these snails, with their long, uncomfortable shells have been at great disadvantage as predators, but have successfully compensated for their handicap thanks to decollation. A process, however, which would have never been possible without their “ability” to seal the shell before chipping of the apex and early whorls.

Polynesian tree snails – saved from oblivion?

Extinct in the wild in its native French Polynesia, Partula faba, a small tree snail, is being given a second chance at Bristol Zoo Gardens, where the last 88 surviving specimens are being nurtured and cared for in an attempt to save the species through conservation breeding.

Newborn Partula faba:15 snails hatched in April 2010 at Bristol Zoo Gardens
(Photo credit: Jenny Spencer)

Double disaster: in the 70s Achatina fulica, a highly prolific species of giant African land snails, was introduced into French Polynesia as a source of food but soon turned into a pest. To keep the highly invasive Achatina under control, a predator snail, Euglandina rosea (rosey wolfsnail) was introduced into the islands. Euglandina however disregarded Achatina and instead devoured local species into oblivion.

According to the IUCN Red List of Threatened Species, of the many Partula species endemic to the islands, by 2009 , 13 were critically endangered, 11 extinct in the wild and 51 extinct (including Partula affinis, P. auriculata, P. bilineata, Partula candida, P. citrina, P. dolichostoma, P. turgida, P. umbilicata and more).