Science1 publisher2 min readPublished
Grooved rear teeth move Britain's smooth snake further along the venom spectrum
Two herpetologists argue in Zootaxa that Britain's smooth snake is venomous, leaving none of the country's three native snakes without venom. The endangered heathland snake is still harmless to people, so the change settles a point of anatomy and hands its conservationists an awkward label.
The Scientist · Science desk
What happened
- Britain has long counted the adder as its only venomous snake, with bites that are rarely life-threatening but still mean a trip to the emergency department.
- Herpetologists Alessandro Paterna and Grégoire Meier argue in the journal Zootaxa that the smooth snake should be reclassified as venomous.
- Their evidence is the snake's rear upper-jaw teeth, which are somewhat grooved and sheathed in gum tissue of the kind rear-fanged snakes use to inject small doses of venom into prey.
- The smooth snake is Britain's rarest snake, confined to lowland heaths in southern England and listed as endangered under IUCN criteria.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- contradiction The paper is framed as a reclassification, but the snake's venom gland has been documented for a century, so the 'new venomous snake' framing overstates how much changed.
- decision Public safety advice stays as it was: the adder remains the only British snake that can harm people, and a smooth or grass snake could at worst leave a few small scratches.
- cost Conservationists protecting Britain's most threatened snake now have to explain a venomous-but-harmless label that the phys.org commentary expects to confuse many people.
Venom in snakes comes in degrees, and the reason is ancestral. Most of the roughly 4,000 living snake species are advanced snakes, or Caenophidia [7]. Their last common ancestor probably lived about 65 million years ago. It is thought to have had small Duvernoy's venom glands, probably with slightly enlarged, grooved teeth at the back of the jaw [7].
Lineages then went separate ways. Vipers and elapids evolved hypodermic fangs, some groups lost the venom system altogether, and many kept a modest version of the ancestral setup, with rear teeth grooved and specialised in some species and barely modified in others [8]. The smooth snake was already on that scale. Its venom gland was discovered more than 100 years ago, and a commentary published by phys.org argues that the new paper nudges the species further along the continuum more than it reclassifies it [9].
The grass snake is the useful comparison. Paterna and Meier note that Natrix helvetica also has venom glands and slightly modified, sheathed teeth, presumably to help it overcome amphibians [11].
The thing this doesn't tell you is how much venom a smooth snake delivers, or what that venom does to a lizard, let alone to a person. The case for harmlessness rests on diet and on the authors themselves. The snake eats lizards and occasionally other snakes or small mammals [5]. Paterna and Meier stress that it is as harmless now as it was before their paper [10].
Rarity is a separate matter. The smooth snake is Britain's smallest snake and is rarely seen in the open [5], so encounters are uncommon. What a bite would do depends on a venom system that evolved to subdue small prey, not animals the size of people [13]. The commentary's comparison is with spiders: almost every native spider is technically venomous, only a couple can pierce human skin, and none produce symptoms worse than a mild local sting [14].
The new label lands on a species that already gets extensive protection. As a European Protected Species, the smooth snake benefits from habitat conservation and from reintroductions to sites it formerly occupied [6].
What to watch
- A study measuring smooth snake venom yield and its effect on lizard prey would put a figure on how far along the spectrum the species sits.
- Whether field guides and conservation bodies adopt the venomous label for the smooth and grass snakes, and how they word it for the public.