THE ASP VIPER – Vipera aspis   Linnaeus, 1758

Inside the Iberian Peninsula the Asp viper is found in the northeast of Spain; it occupies the entire Pyrenees and the pre-Pyrenees, reaching the province of Burgos and the north of Soria to the west. In the rest of Europe it is distributed more or less continuously through France, Italy, Switzerland and the extreme southwest of Germany.

Description: With up to 80 cm (31,5 inch) of maximum body length Vipera aspis is the largest of the three viper species which inhabit the Iberian Peninsula. However, the average size is between 60 and 65 cm (23-26 inch). The head is triangular shaped and the snout is slightly upturned, although not as prominent as in Vipera latastei.

Vipera aspis
Vipera aspis - photo: Daniel Gómez
Vipera latastei
Vipera latastei - photo: Juan Timms

A postocular stripe is present, more noticeable in males. The pupil is elliptical and is always kept in a vertical position. Generally the males are grey in colour while the females are grey or brown.

Biology: The more alpine populations tolerate lower temperatures, however their activity period is reduced to just five or six months during the year. Specimens which inhabit lower altitude zones have an activity period of seven or eight months. This species shows a marked diurnal activity. In general terms Vipera aspis shows greater activity patterns than Vipera latastei, and it is also more abundant; the number of specimens per square kilometre in a given population is considerably greater in Vipera aspis.

Feeding: The Asp viper is a diurnal predator which lies in wait for prey. It uses its venomous apparatus to kill the prey. Adult specimens feed primarily on rodents, completing their diet with lizards and small birds. It normally takes about a week to digest an item prey, and in the wild they will feed every three or four weeks. Juveniles feed almost exclusively on lizards.

Reproduction: Females usually have a biannual reproductive cycle. The copulations occur between April and May, several weeks after hibernation.

The gestation period lasts between three to four months and birth takes place by the end of August or the beginning of September.

An average of 6 or 7 perfectly formed baby vipers are born which will realize their first shedding shortly after birth. A few days later the young will start feeding.

Vipea latastei
Vipera aspis aspis, newborn - photo: Raúl doblado

Venom: Even though an adult healthy human being can overcome an Asp viper bite without too many complications, certain kind of people such as children and elderly or unhealthy persons may suffer serious complications which could be fatal. Hence, a bite should always be monitored by a doctor and treated in a hospital.

Vipera aspis venom registers an LD50* of 4,6 to 20,1 mg (Duguy and Saint-Girons, 1970; Saint-Girons et al., 1983). The lower values correspond to Vipera aspis zinnikeri which means it is the subspecies with the most toxic venom, thus making it the most dangerous viper in the Iberian Peninsula.

• LD50: (Lethal Dose 50% or median lethal dose) is the dose required to kill half the members of a tested population (laboratory mice) after a specified test duration. Expressed in milligrams, it indicates the degree of toxicity of a venom; lower values of LD50 indicate a higher toxicity.

Subspecies: Currently there are two subspecies of asp viper recognized in the Iberian Peninsula; Vipera aspis aspis and Vipera aspis zinnikeri. Some authors have suggested the possibility of classifying Vipera aspis zinnikeri as a separate species.

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