Why Do Lizards Drop Their Tails? Tail Autotomy Explained

How do lizards drop their tails?

Tail dropping is not a random injury. Lizards that can do it have special zones of weakness, called fracture planes, built into the bones of the tail. In most such species, each tail vertebra has a thin, unossified plane across the middle where it can split cleanly. This is called intravertebral autotomy. In a few groups, the tail breaks between two vertebrae instead.

When the tail is seized, the lizard contracts muscles around one of these planes and the tail snaps off. Muscle bundles in the tail are arranged in sections that pull apart neatly, and ring-shaped muscles squeeze the main tail artery shut, so very little blood is lost. Flaps of skin and muscle then close over the wound.

Most lizards drop the tail only when it is grabbed with enough force. Some geckos can throw it off with almost no pulling at all, for example when they are swarmed by ants. Autotomy has been recorded in roughly 13 of about 20 lizard families, which shows how useful this defense has been in lizard evolution.

Why does a dropped tail keep wriggling?

A detached tail does not simply lie still. Its nerves and muscles keep firing for minutes, making it twist, jump and thrash. In the leopard gecko, a dropped tail can keep twitching for up to about 30 minutes.

The movement is the point. A predator such as a bird, snake or cat often turns its attention to the wriggling tail, giving the lizard a few vital seconds to dash into cover. Some species make the decoy even more eye-catching. Juvenile five-lined skinks of the eastern United States and many young lizards elsewhere have bright blue tails, and studies show that such colors draw attacks toward the tail rather than the head and body.

What does a lizard lose when it drops its tail?

Autotomy saves lives, but it is expensive, which is why lizards use it only as a last resort. The costs depend on what the tail does for each species:

• Lost energy reserves. In geckos such as the leopard gecko, the tail is a major fat store. Losing it means losing food reserves for lean seasons and winter. Some lizards return to eat their own dropped tail after the danger has passed, recovering part of that energy.
• Lower breeding success. Female Texas banded geckos that have lost their tails produce smaller eggs or none, and in some lizards males without tails find fewer mates.
• Lower social status. In the side-blotched lizard of western North America, tail loss can lower an individual’s rank among rivals.
• Changes in movement. Tails help with balance, climbing and jumping. Some lizards run faster without the extra weight, but others become slower or clumsier until the tail regrows.
• One less defense. A lizard with a short new tail has less to offer the next predator.

To limit these costs, many lizards become more cautious after losing a tail, staying closer to cover and moving less until it has regrown.

How does the tail grow back?

Most lizards that can drop their tails can also regrow them, usually over several weeks to a few months. The new tail is not a perfect copy. Instead of a chain of bony vertebrae, it is supported by a single tube of cartilage, and it has no fracture planes. Its scales are often smaller and more uniform, and its color and pattern frequently differ from the original, as in the pale, regrowing tail of the wall lizard pictured on this page.

Because the regrown section cannot break again, a lizard that loses its tail a second time must lose it closer to the body, at a fracture plane in the original part. Sometimes a tail breaks only partly and a new tail grows from the crack while the old one stays attached, producing a forked or even three-pronged tail. Regrowth also uses a lot of energy, which can slow body growth while it happens.

Which lizards can and cannot drop their tails?

Tail autotomy is common in geckos, skinks, wall lizards and their relatives, many iguanas and anoles, and legless lizards. The slow worm of Europe owes its scientific name, Anguis fragilis, to how easily its tail breaks. Older slow worms often have a short, blunt tail tip where a lost tail has healed. Learn how to tell it apart from a snake in Is a slow worm a snake?

Several lizard groups cannot drop their tails at all. Chameleons, which use their tails to grip branches, lack fracture planes, and so do monitor lizards. Most agamid or “dragon” lizards, including the central bearded dragon, also lack them. In these species a tail lost through injury does not regrow.

Tail dropping in other animals

Lizards are not alone. Many salamanders shed their tails, and some can regrow an almost perfect copy, including bones. The tuatara of New Zealand and a few snakes can lose part of the tail too. Among mammals, certain African spiny mice can shed tail skin or patches of body skin and regrow them with little scarring.

Many invertebrates use the same strategy. Crabs can drop claws, spiders and harvestmen can shed legs, and some octopuses and sea slugs can release arms or body parts. In all of these, giving up a part of the body is better than being eaten.

Myths and facts about lizard tails

Myth: Picking up a lizard by the tail is harmless. Fact: It can trigger autotomy and cost the lizard its fat reserves and its best defense. Wild lizards are best watched without handling.

Myth: A regrown tail is identical to the original. Fact: It has cartilage in place of vertebrae and usually looks different.

Myth: Every lizard can drop its tail. Fact: Chameleons, monitor lizards and most dragon lizards cannot.