How Long Do Slow Worms Live? Surprising Lifespan Records

How long do slow worms live in the wild?

The honest answer is that nobody knows precisely. The slow worm spends most of its life hidden under logs, stones and vegetation or underground, so following individuals for decades is extremely difficult. Field researchers can mark and recapture animals, but few studies have run long enough to measure maximum ages.

What we do know is that slow worms live slowly. Newborns are only about 7–10 cm (3–4 in) long, they grow little before their first winter, and they pass about 20 cm (8 in) at around two years of age. They do not mature until about 3–5 years old. After that, growth slows down even further.

Anecdotal reports suggest that wild slow worms can live up to about 30 years. Most individuals certainly die much younger, because slow worms are eaten by a long list of predators, from badgers and hedgehogs to birds of prey, crows, adders and domestic cats.

Old age shows in small ways. Very old slow worms often have lost some of their teeth, and many adults carry scars from fights or a blunt tail stump where the tail was once shed.

The 54-year record at Copenhagen Zoo

The most famous slow worm in the record books is a male that lived at Copenhagen Zoo in Denmark from 1892 until 1946, a span of about 54 years. Because he was already an adult of unknown age when he arrived, his true age was probably higher. Some sources treat 46 years as the best-documented captive age and give the 54-year figure with more caution.

These figures come from long-term zoo records compiled in longevity databases. They are captive ages, and captive animals are protected from predators, disease outbreaks, hard winters and food shortages. Still, they show that the slow worm’s body is capable of lasting more than half a century, an extraordinary span for a lizard that weighs only a few tens of grams.

Why do slow worms live so long?

Biologists see a general pattern across animals: species that grow slowly, mature late and breed at a modest rate tend to live longer. The slow worm fits this pattern well:

• Late maturity: it takes about 3–5 years to reach breeding size.
• Slow breeding: females do not breed every year. In the Netherlands, for example, only about 30% of females become pregnant in dry years, though up to 90% may do so in wet years.
• A long winter rest: in central Europe and Britain, slow worms hibernate underground for about half the year, usually from October to March or April.
• A low-energy lifestyle: like other reptiles, slow worms are cold-blooded, need far less food than a mammal of the same size, and spend much of their active season resting in cool, hidden places.
• Good protection for adults: bony plates under the scales, a hidden lifestyle and the ability to shed the tail help adults survive attacks.

Together, these traits mean that slow worms “live slow,” and in a safe environment their bodies age slowly too.

How does the slow worm compare with other lizards?

The slow worm is often called the longest-lived lizard, but records for other species are less certain, and a few rivals exist:

Compared with the short-lived panther chameleon, which rarely survives more than a year or two in the wild, the slow worm is a marathon runner. The tuatara of New Zealand has lived around 90 years in captivity, but it is not a lizard at all; see is a tuatara a lizard?. Our list of longest-living animals covers the record holders across the animal kingdom.

Among British reptiles, the slow worm also outlasts the common European adder, which usually lives about 10–15 years in the wild.

What shortens a slow worm’s life?

Most slow worms never come close to their potential lifespan. The main causes of death include:

• Predators: badgers, hedgehogs, foxes, birds of prey, crows, pheasants, adders, smooth snakes and, for young ones, thrushes, shrews and toads.
• Domestic cats: in gardens, cats catch and injure many slow worms.
• Mowing and strimming: slow worms hiding in long grass are easily hit by machines.
• Roads and paths: they often lie on warm tarmac in the evening and are run over.
• People: many are still killed by people who mistake them for snakes.
• Hard winters and dry summers: poor conditions can reduce food and breeding.

Losing the tail is not fatal, but it has a cost. In many lizards the tail stores fat reserves, and a slow worm regrows only a short stump, so it has less tail left to sacrifice in the next attack.