The ‘third’ British snake, the Smooth Snake (Coronella austriaca), is one I have never seen. Of limited distribution, heathland in parts of the south of England, it also occurs widely in continental Europe. Until a few weeks ago the way in which it feeds was thought to be simple. In terms of prey though the preference or availability appears to vary. In Britain small mammals are taken more frequently than lizards; in Italy lizards are the main prey. Young smooth snakes seem to rely heavily on small lizards although they have even been known to eat bluebottles and spiders.
All observers have agreed that once caught in the jaws, the prey is manipulated in to a position where it can be more easily swallowed. During this process coils of the body may help to subdue but not constrict the animal that has been caught. The unfortunate mouse, shrew or lizard is then swallowed alive. Thus the smooth snake was considered to neither venomous nor a constrictor. That is the standard story but in their New Naturalist series book Trevor Beebee and Richard Griffiths raised the point, ‘…so how the snake escapes severe bites from these mammals is not at all clear’. The recent research suggests how that how is achieved.
The authors of the new study, Alessandro Paterna and Grégoire Meier, rely, first, on their own evidence from an anatomical study of the teeth and jaws and, second, on experiments on the closely related species, Coronella girondica, the Southern Smooth Snake, the results of which were published in 1922 in France. In both species they found fangs on the posterior maxilla, the bases of which are enclosed by a sheath. The sheath enables secretion Duvernoy’s gland to be delivered into a wound caused by the fangs. In other words there is every reason to suspect that whole arrangement acts for the conveyance of a noxious secretion into the wound, especially in circumstances where the bite is prolonged and there is time for such a low-pressure system aided by chewing motion of the jaws to work.
There has been endless discussion of whether secretions from Duvernoy’s gland should be called venom and I will not prolong that agony. However, using the term venom for any combination of chemicals used by a predator to the detriment of its prey the question is: does Duvernoy’s gland in this species produce venom? Here one the authors provided useful anecdotal evidence:
…in a field study in the Laga Mountains in the province of Teramo (Abruzzo), one of us (AP) was bitten by an adult male Coronella austriaca while handling the specimen. The bite was prolonged, allowing time to take a photograph while the “mastication” action was still in progress…Following the bite, itching and redness quickly appeared in the affected area. A second photograph, taken 11 minutes after the photo showing the bite, shows redness corresponding to the maxillary arch’s shape, where the holes caused by some anterior maxillary teeth and the pair of posterior fangs
are visible. Over time, in addition to the redness, swelling developed at the site of the small lacerations caused by the teeth, which was also accompanied by itching. The most evident symptoms lasted a few minutes, then gradually subsided in less than an hour. As researchers in both field and controlled environments, we both frequently receive snake bites in different contexts. Nevertheless, this case, although extremely mild, represents the only one to date in which we have personally observed a reaction other than bleeding following a bite of a colubrine snake.
If the bite resulted in irritation to human skin, what about potential prey? Here Marie Félicie Phisalix (née Picot)(1861-1946), who worked in Paris and was one of the leading experts on snake venoms in the first half of the 20th century, provided experimental evidence which I am surprised nobody gathering information on smooth snakes seems to have taken on board earlier.
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| Marie Physalix in 1929 Autochrome by George Chevalier |
Marie Phisalix prepared material for injection from whole, dried Duvernoy’s glands. The gland is tiny. She noted in the largest snakes it only weighed 1 mg when dried (equivalent to around 4 mg wet weight). Since it is not known how much secretion would reach a bitten animal, the results show the sort of maximum effect that could be achieved. The findings though were pretty spectacular. An extract from two glands given intravenously to a rabbit put it into a state of torpor for 10 minutes. It then died after 15-20 minutes of respiratory arrest. Six glands-worth killed an adult guinea pig. A green lizard showed transient narcosis after a two-gland dose.
These experiments do suggest the presence of powerful agents in Duvernoy’s gland of smooth snakes. However, I can hear my former and late colleague sitting on my shoulder warning that some of the effects could be due to the presence of extraneous substances like bacterial toxins from the mouth and I do hope that the recent work is being followed up to see what biologically active substances are present in the Dubernoy’s gland of smooth snakes. Secretions from the gland of other rear-fanged species have been studied, for example by Robert Hill and Stephen Mackessy in 2000, and a comparison with such findings is now essential.
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| Smooth Snake The colour plate from Malcolm Smith's The British Amphibians and Reptiles published in 1951 in the Collins New Naturalist Series Photograph by Walter Sydney Pitt (1900-1983) |
It would seem though that the evidence is highly suggestive of a rear-fanged, low pressure venom delivery system. Observations on C. austriaca collected by Malcolm Smith for his New Naturalist series book published in 1951 indicate that some items of prey, small lizards for example are caught and swallowed quickly. However, larger prey like small mammals with the capacity to bite back may be held onto for longer, allowing noxious agents from Duvernoy’s gland to seep into the wound, enter the bloodstream and render the mouse, vole or shrew quiescent.
Thus it seems we should now consider the Smooth Snake to be Britain’s second venomous snake with the proviso that the venom is so weak that even if a human being were to be bitten the only effect would be slight and temporary inflammation in the area surrounding the puncture marks. Perhaps we should just say Britain still has two snakes that are entirely harmless to the human population.
Paterna A, Meier G. 2026. Reclassification of the smooth snake. Analysis of the rear fangs, venom system, and the cephalic anatomy of Coronella austriaca (Serpentes: Colubridae). Zootaxa 5873 (1): 145–160. https://doi.org/10.11646/zootaxa.5873.1.8
Phisalix M. 1922 .Animaux Venimeux et Venins. Vol. 2. Paris: Masson et Cie,
Beebee TJC, Griffiths RA. 2000. Amphibians and Reptiles. A Natural History of the British Herpetofauna. London: HarperCollins.
Smith M. 1951. The British Amphibians and Reptiles. London: Collins.
Hill RE, Mackessy SP, 2000. Characterization of venom (Duvernoy’s secretion) from twelve species of colubrid snakes and partial sequence of four venom proteins. Toxicon 38,1663-1687 https://doi.org/10.1016/S0041-0101(00)00091-X
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