The Rosy Wolf Snail (Euglandina rosea)


Rosy Wolf Snail (Euglandina rosea), adult specimen.
Picture by courtesy of: Jim Miller, Jacksonville Shell Club.
 

Wolf snails are are part of the mainly neotropic land snail family of Oleacinidae, whose area of distribution spread from Southern and Central America up into the South Eastern United States. Some species, though, also settled in the area of the Mediterranean.

In Florida, for example, the rosy wolf snail, Euglandina rosea (Férussac 1821), may be found, a predator snail about 10 cm long, in contrary to other predator snails a specialised snail-eater.

A European member of the family is the Dalmatian predator (Poiretia cornea), that can be found in the Mediterranean and especially hunts for small operculate land snails (like the round-mouthed snail, Pomatias elegans). 

Euglandina and Poiretia both even bear an external resemblance: They share an elongate oval shell with an visibly extended last whorl and a strikingly large aperture.

 
Movie clip: A rosy wolf snail (Euglandina rosea) on its way.
Interesting: The lips' movement! Source: YouTube.

Looking closely at a wolf snail's head, it appears to have three pairs of tentacles. The longer eye stalks can easily be seen, as well as the shorter tentacle pair below. Below these there appears to be a third pair of tentacles. Only, this is actually not a pair of tentacles, but the wolf snail's greatly elongated lips. 


Euglandina rosea
on the title of „Science”
(Vol. 285, Sept. 99). Source: R.H. Cowie
 

A terrestrial snail's lips are full of chemical sense cells, by the help of which the snail can search the ground for food. In the case of the wolf snail, the lips are used to follow the prey's scent along its slime trace. Which a wolf snail does, like a wolf follows the scent of its prey, hence the snail's name. Only in the case of the wolf snail, it is more precisely the taste, not the scent, which it follows. 

From another snail's slime trace the wolf snail also gains information on whether the snail is a potential meal rather than a fellow wolf snail. Which basically makes not much of a difference, as wolf snails also are cannibals.

On pursuit of its prey the wolf snail does not move at a proverbial snail's pace, but at double or triple that speed. It follows its prey up trees and even for certain distances under water.

As wolf snails are not only snail-eaters, but also cannibals, even the young snails already feed on eggs and their siblings. Generally wolf snails prefer smaller snails, that can be eaten whole with the shell. The advantage for the wolf snail is obvious – so it can eat the snail and consume calcium carbonate from the shell. The American malacologist G. Lee reports to have found at least 13 snail shells in a dissected specimen of Euglandina rosea. ("Shells are where you find them").

 
Euglandina feeds on a Bradybaena similaris.
Picture by courtesy of: Bill Frank, Jacksonville 
Shell Club
.

While it eats smaller snails whole, larger prey is eaten piecemeal. The wolf snail's slender body enables it to reach the innermost parts of the prey's shell and to eat it until the last portion.

Wolf snails also eat slugs. In experiments it has been found that small garden slugs (Deroceras) managed to evade a wolf snail attack by hectically waving the tail, obviously trying to stop it from getting a grip with the radula. 


Partula clara from Tahiti. Some small populations have survi-
ved in spite of the wolf snail. Picture: Trevor Coote, IUCN.
 

Wolf snails have been introduced as a biological weapon against the giant African land snails (Achatina fulica) that had previously been brought to several Pacific islands (Hawaii, Mariana islands, Polynesia) for economical reasons.

Instead to eat the giant African snails, that had become a large pest problem for local agricultural areas, the wolf snails preferred to hunt the smaller endemic tree snails (Partula, Achatinella, among others), obviously more in their prey scheme of small terrestrial snails.

The usually quite small populations of endemic tree snails were vulnerable against the increase selective pressure of the wolf snail predation. As a consequence, today many of those tree snail species are estimated to be extinct and must be though to be invariably lost.

Wolf snail feeding behaviour already well known and documented, the consequences of such an intrusion into an endemic ecological system should have been predictable. Alas, the local authorities disregarded the warnings of worried malacologists and ecologists.

Further Information:


Two wolf snails mating – a dangerous business? Picture by courtesy of: Bill Frank, Jacksonville Shell Club.

Systematics and related species

 
A predatory snail of the Streptostyla genus from Honduras.
Picture: John Slapcinsky, Source: Flickr.
Subclass: Pulmonata
Superorder: Eupulmonata
Order: Stylommatophora
Suborder: Sigmurethra
Superfamily: Testacelloidea
Family: Oleacinidae Adams & Adams, 1855
Subfamily: Euglandininae Baker, 1941
Genus: Euglandina Fischer & Crosse, 1870
Genus: Poiretia Cuvier, 1800
Subfamily: Streptostylinae Baker, 1941
Genus: Streptostyla Shuttleworth, 1852
 
Systematic classification according to Fauna Europaea
(Bank, R., 2011).
 

The rosy wolf snail is a part of the Testacelloidea superfamily, present with many other predatory snail species in Mediterranean Europe, but especially in North, Central and South America. In a very simplifying manner, the family Oleacinidae is referred to as "predatory snails" in German, but of course those snail species by no means are the only predatory terrestrial snails.

Like the superfamily name Testacelloidea indicates, they are related to the shell slugs of the Testacella genus, present mainly in Western Europe, carrying a little shell rest on their back. The Oleacinidae, however, can withdraw completely into their large, elongate shell.

Among the European species of the Oleacinidae family, there are, for example, the Mediterranean predatory snails of the Poiretia genus, with the Dalmatian predator, Poiretia cornea, one of them. They share a subfamily with the wolf snails of the Euglandina genus (there are more species more to the south, in Central America). A further subfamily are the Streptostylinae from Central and adjacent South America (see picture above), whose external similarity to Euglandininae is quite striking.


The head of the Dalmatian predator (Poiretia cornea), from
Montenegro in former Yugoslavia. Picture: Cédric Audibert.
 

Interestingly, both Euglandininae and Streptostylinae possess the characteristic lips extended to a third tentacle pair. The European genus Poiretia does not.

Apparently, there is no consent about the systematic classification of the mentioned snail groups. While one side, like the malacologists Ruud Bank on Fauna Europaea, and Francisco Welter-Schultes on AnimalBase, stay with the classification as described above, there is another direction mainly on American pages according to the publication of Thompson in 2010, so the subfamilies Euglandininae and Streptostylinae are supposed to belong to the Spiraxidae family together with the Spiraxinae subfamily, following H. B. Baker (1962).

Links and Literature Accessed: 13.05.2011.

  AnimalBase: Poiretia genus homepage.
  Fauna Europaea: Oleacinidae.
  Wikipedia (English Version): Spiraxidae.
  Thompson, F. G. (2010): "Four species of land snails from Costa Rica and Panama (Pulmonata: Spiraxidae)". Revista de Biología Tropical 58(1): 195-202. PubMed (PDF).