Asp Viper

Fascinating facts about the Asp Viper

• Only about 4% of untreated bites from this viper prove fatal, yet the pain can be excruciating and swelling appears within minutes. The bite can cause rapid tissue death and even vision loss as blood vessels in the eyes break down. It shows how a small snake can pose a serious medical emergency in remote mountain villages.
• Males can grow up to 85 cm long, while females rarely exceed 75 cm, and the average adult measures 60–65 cm. The male’s body is slightly slimmer and its tail makes up one-sixth to one-eighth of its length, compared to one-seventh to one-ninth in females. These size differences help researchers tell the sexes apart in the field.
• In the Pyrenees this viper has been recorded at elevations well over 2,100 m (6,900 ft), thriving on sunny slopes and stone quarries high above the tree line. Such altitude tolerance is rare for venomous snakes in Europe. It reminds us that even the harshest mountain climates can host hidden predators.
• Laboratory tests give the venom an LD50 of 1.0 mg per kilogram when injected intravenously and 1.0–2.0 mg/kg subcutaneously, with a slightly higher 4.7 mg/kg value for intramuscular injection. Daily venom extraction yields only 9–10 mg, indicating a low overall output per snake. These numbers explain why a single bite can be lethal despite the modest amount of poison delivered.
• The IUCN listed the species as Vulnerable in 2022 after a decline of more than 30% over the past 24 years, roughly three generations for the snake. Some subspecies are even more at risk, with one classified as Critically Endangered in Switzerland. This rapid drop highlights how quickly habitat loss and climate change can push a once-common reptile toward the brink.

At a glance

About the Asp Viper

The Asp Viper, Vipera aspis, is a modestly sized European viper averaging 60–65 cm in total length, with males occasionally reaching 85 cm and females rarely exceeding 75 cm. Its broad, triangular head sits on a short tail that makes up just one-sixth to one-ninth of its body, and the upturned snout gives it a distinctive profile. The dorsal surface is covered in 21–23 rows of strongly keeled scales, while the ventral count ranges from 134 to 170, varying among subspecies. Its coloration is highly variable, seldom forming the classic zigzag of its cousin V. berus, and the eye, about as tall as the distance to the mouth, stares from a crown of small, mostly smooth scales. In the sun-baked limestone hills and low mountains of France, Italy, Switzerland and neighboring countries, this snake favours warm, sun-exposed slopes, scrublands, forest clearings and even stone quarries, often at elevations well over 2 100 m in the Pyrenees. It thrives where dry soils meet structured vegetation, seeking cover in leaf litter or under rocks. Its venom’s dual nature, with a relatively low yield of about 9–10 mg per day, combines potent coagulant and anticoagulant effects, producing rapid, excruciating pain and, in untreated cases, a fatality rate of roughly 4 %.

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