Autotomy facts for kids
Imagine an animal that can drop a body part on purpose to escape danger! This amazing ability is called autotomy. The word comes from ancient Greek and means "self-amputation" or "self-severing." Animals use autotomy as a clever trick to get away from predators. If a predator grabs them, they can shed a limb or their tail. This distracts the attacker, giving the animal a chance to flee.
Many animals that use autotomy can also regrow the lost body part later. This regrowth, called regeneration, can take weeks or months. Scientists believe autotomy has developed independently in many different animal groups over time. The term was first used in 1883 by a scientist named Léon Fredericq.
Animals with Autotomy
Reptiles and Amphibians
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Some reptiles and amphibians, like many lizards, salamanders, and even some snakes, can drop their tails if a predator catches them. This is a fantastic way to escape! The detached tail often keeps wiggling for a while. This movement tricks the predator into thinking it still has the animal, allowing the real animal to run away.
Some lizards, like the blue-tailed skink, even have brightly colored tails. These bright colors can draw a predator's attention to the tail, protecting the lizard's main body and head. After losing a tail, many species can regrow it. However, the new tail is often shorter and made of cartilage instead of bone. Its color and texture might also look different from the original. But some salamanders can regrow a tail that looks exactly like the old one!
How Tail Dropping Works
The special term for dropping a tail is 'caudal autotomy'. In most lizards, the tail only breaks off if it's grabbed with enough force. But some animals, like certain geckos, can drop their tail just from being very stressed, for example, if ants attack them.
Lizards have two main ways to drop their tails. Sometimes, the tail breaks between two vertebrae (the bones in the spine). Other times, the tail has special weak spots, called fracture planes, right across the middle of each vertebra. In this case, the lizard uses a muscle to snap the bone itself. After the tail breaks, special muscles in the tail squeeze tightly around the main blood vessel. This helps stop the bleeding quickly. Skin flaps also fold over the wound, sealing it to prevent infections. This amazing ability to drop tails is common in lizards, found in many different families.
Why Autotomy is a Big Deal
Dropping a tail is a great way to escape predators, but it's a last resort. It comes with some costs. For example, regrowing a tail takes a lot of energy. This can temporarily weaken the animal's immune system, making it more vulnerable to sickness. The tail is also important for movement and storing fat, so losing it means losing valuable resources.
After dropping a tail, many lizards become less active. This helps them save energy while their new tail grows back. Some clever lizards even return to their dropped tail after the danger has passed and eat it! This helps them get back some of the nutrients they lost. Interestingly, some lizards will even attack the tails of their rivals and eat them after the opponent flees.
Some animals have developed ways to lessen the costs of autotomy. For instance, the very toxic salamander Bolitoglossa rostrata will wait to drop its tail. It only does so if a predator holds on for a long time or moves its jaws further up the tail. This allows the salamander to keep its tail if its toxicity alone can scare off the predator. Regrowing the tail is a top priority after autotomy. This helps the animal move well again and be ready for reproduction.
Ancient Tail Droppers
Scientists have found fossils of ancient reptiles that could drop their tails. These fossils date back to the Late Carboniferous and Early Permian periods, millions of years ago. This shows that autotomy is a very old survival trick! Some Jurassic period lizards, like Eichstaettisaurus schroederi and Ardeosaurus digitatellus, also had these special tail-breaking points. They are thought to be ancestors of today's geckos.
Mammals with Shedding Skin
Did you know some mammals can shed their skin? Two types of African spiny mice, Acomys kempi and Acomys percivali, can release their skin if a predator grabs them. What's even more amazing is that they can completely regrow the lost skin, including hair, sweat glands, and even cartilage, with almost no scars! They are the first mammals known to do this.
Other rodents, like cotton rats and eastern chipmunks, have a different trick. Their tail skin can easily slide off, leaving the bare bones of the tail behind. This is sometimes called "false caudal autotomy."
Fishy Escapes
The giant oarfish is a mysterious deep-sea fish that can also practice autotomy. It can shed the back part of its body, sometimes just its tail fin, or even a large section of its body behind its main organs. Since its vital organs are all in the front, these amputations don't harm it. Oarfish often do this multiple times in their lives. Almost all oarfish longer than 1.5 meters (about 5 feet) have shorter bodies because of this. Scientists aren't sure why they do it, as oarfish don't seem to have many natural predators.
Invertebrates with Autotomy
Over 200 different kinds of invertebrates (animals without backbones) use autotomy. They can voluntarily shed body parts when they need to survive. This can happen if they are touched, stung, or grabbed by a predator. Autotomy helps them escape or prevents further harm, like stopping a toxin from spreading.
Molluscs: Slugs, Snails, and Octopuses
Some octopus species use autotomy for both survival and reproduction. The male octopus has a special arm that detaches during mating and stays with the female.
Certain land slugs, like those in the genus Prophysaon, can drop part of their tail. The sea snail Oxynoe panamensis also sheds its tail if it's bothered a lot.
Many sea slugs are masters of autotomy. Some, like Discodoris lilacina, will drop their entire outer skirt-like body part if handled. Even more incredible, young specimens of two Elysia sea slug species can regrow their entire body from just their head! They do this if they are attacked by internal parasites. These sea slugs are also special because they can use parts of algae to perform photosynthesis, which helps them survive after losing their digestive system.
Crustaceans: Crabs and Lobsters
Stone crabs are famous for their ability to regrow claws. People harvest these crabs by removing one or both claws and then returning the crab to the ocean. The crab then regrows its lost limb(s). However, studies show that many crabs do not survive this process, especially if both claws are removed.
Sometimes, crabs and lobsters in fisheries will drop their legs after being caught. This can happen if they are exposed to fresh water or very salty water.
Spiders: Losing Legs to Live
Orb-weaving spiders, like those in the Argiope family, will drop a leg if a wasp or bee stings it. Scientists have found that if they inject spiders with venom components that cause pain in humans, the spiders will drop their legs. But if they inject just saltwater, the spiders rarely drop a leg. This suggests the pain or irritation from the venom triggers the autotomy.
Autotomy can also play a role in spider reproduction. The male of some spider species, like Nephilengys malabarensis, will detach a special part of its body during mating. This helps the male escape after mating and protect the female from other males.
Bees and Wasps: A Costly Sting
When a honey bee (from the genus Apis) stings a victim, especially a mammal, its barbed stinger can get stuck. As the bee tries to pull away, the stinger tears off part of its abdomen. This severe injury unfortunately kills the bee. However, a queen honey bee's stinger is not barbed, so she can sting without harming herself. Some wasp species also use sting autotomy as a defense.
Male honey bees, called drones, also lose a part of their body during mating. This helps secure the queen and unfortunately means the male bee dies soon after.
Echinoderms: Sea Cucumbers and Starfish
Evisceration is a type of autotomy seen in sea cucumbers. When they are stressed, they can eject their internal organs. Amazingly, they can then regrow all the lost organs!
Some starfish can shed their arms. Even more incredible, a single lost arm may sometimes be able to regrow into a whole new starfish!
See also
- Ainhum
- Anti-predator adaptation
- Autoamputation
- Evisceration (autotomy)
- Self-amputation
