Great Britain has always been thought to be home to a single venomous snake species, the adder. Although its bites are rarely life-threatening, they will require a trip to A&E and more than likely ruin your week. On the other hand, the other two native British snakes, the grass and smooth snakes, have been largely considered non-venomous.
This status quo has been shaken by a new paper by herpetologists Alessandro Paterna and Grégoire Meier suggesting that the smooth snake should be reclassified as venomous. The teeth at the back of its maxilla (the outer upper jaw) are somewhat grooved. They are surrounded by a sheath of gum tissue typical of so-called rear-fanged snakes, which can inject small quantities of venom into their prey.
Inevitably, this discovery generated lively headlines and plenty of questions. How could the venomous nature of a native British snake have been overlooked for so long? Have we suddenly discovered a previously unrecognised menace lurking in the English countryside?
To start, the smooth snake (Coronella austriaca) is by far the rarest British snake, being restricted to lowland heaths in southern England, where it is listed as endangered under International Union for Conservation of Nature criteria.
As Britain’s smallest snake, it lives a discreet life. It feeds on lizards as well as occasionally other snakes or small mammals, and is rarely seen in the open. Due to its rarity and status as a European Protected Species, it benefits from extensive conservation measures to preserve its habitat, and reintroductions to formerly occupied sites.
What’s really new?
For biologists, these new findings aren’t a plot twist so much as a loose end being tied up. Most of the 4,000 or so snake species alive today belong to a group known as the “advanced” snakes (Caenophidia). Their last common ancestor, which probably lived around 65 million years ago, is thought to have already had small venom-producing glands (known as Duvernoy’s venom glands), probably with slightly enlarged, grooved teeth at the back of the jaw.
From that shared starting point, different snake lineages went in different directions. Some evolved the hypodermic-needle fangs of vipers and elapids – the snakes most of us picture when we hear “venomous”. Others lost their venom system altogether. But many kept a modest version of the ancestral set-up: small glands at the back of the mouth, paired with teeth that are grooved and specialised in some species, barely modified in others.
Venomousness in snakes isn’t a switch that’s simply on or off. It’s a spectrum, running from no venom apparatus at all through to the fully developed fangs of a viper.
Seen this way, the discovery of the smooth snake’s more specialised rear teeth isn’t especially surprising. Its venom gland had been discovered over 100 years ago, so the new paper doesn’t so much “reclassify” it as nudge it further along this continuum.
Venomous does not mean dangerous
Of course, the new discovery does not change the smooth snake. It remains as harmless now as it was before the paper, as emphasised by Paterna and Meier themselves.
The idea that a snake can be both venomous and harmless may appear counterintuitive. But wherever you’re now reading this, you are almost certainly within a few metres of a free-living, unconfined venomous animal: a spider. Almost every native spider is technically venomous – that’s how they subdue insects. Yet only a couple can even pierce human skin, and none produce symptoms worse than a mild local sting.
The same logic applies to the smooth snake, whose venom system evolved to subdue small prey, not larger animals like us. As Paterna and Meier note, this also true of our native grass snake (Natrix helvetica). This snake likewise has venom glands and slightly modified, sheathed teeth, presumably to help overcome amphibians. Paradoxically, Britain thus turns out to have no native non-venomous snakes at all. But only the adder can be harmful to us, whereas the other two could at worst inflict a few small scratches.
For conservationists, the news that Britain’s most threatened snake is technically venomous is something of a PR dilemma. To many people, the distinction between venomous and dangerous is more likely to confuse than clarify.
Ultimately, most people will be concerned with one question only: is this snake a threat to me, my children, or my pets? The simplest, most accurate answer remains what it always was: the smooth snake is harmless.
The venom story is a fascinating elaboration of existing ideas for herpetologists. For everyone else, it changes nothing at all.
