A cocoon is any type of organic structure that encloses or surrounds an organism. While most people have heard about cocoons in relation to caterpillars, which transform inside of cocoons and come out as moths or butterflies, a wide variety of other organisms also use them for a variety of different purposes. As a result, there are several kinds of cocoons that exist in nature, all of which have their own distinct characteristics.
Holometabolic cocoons are the most well-known variety. According to Cocoon.org, the insects that make them, such as moths and butterflies, undergo a specific type of life cycle, known as holometabolism, wherein they complete four stages. These stages are egg, larva (caterpillar), chrysalis (cocoon) and finally adult (butterfly), when the insect is sexually mature and can start the cycle again for the next generation. Holometabolic cocoons come in a variety of shapes and sizes. For example, the Cecropia moth's larvae produce brown, hammockstyle cocoons that hang between two objects, while the silkworm's larvae create egg-shaped, white cocoons, which are fluffy in appearance.
Unlike holometabolic insects, bees do not have four distinct life stages. Instead, they go through the larva and chrysalis stages while still inside of eggs. However, this does not mean that bees do not ever utilise cocoons. According to Cocoon.org, once bees hatch, worker bees go around to the newborns and cover them with a special type of jelly that they can secrete from glands on their heads. The young bees form this jelly into a tight coating around them, and use it for sustenance before moving on to pollen, nectar and other sources of food.
Spiders are the most well-known creatures when it comes to spinning silky cocoons for containing and protecting developing eggs. You may have noticed some of these before in the corners of your ceilings or in an attic or basement. The ladybird spider, for example, spins a silk cocoon for its eggs and then covers it with debris for camouflage. It transports the cocoon down into a burrow each night for safekeeping, and brings it to the surface again each day.
Many different aquatic and amphibious animals develop with a coat of slime, such as frogs and salamanders. However, one organism that produces an incredibly distinctive slime cocoon is the hagfish, which is an eel-like creature with no fins. The scavenging hagfish uses the slime as a defence mechanism when it is threatened. The slime oozes out of the hagfish's body and forms a thick, protective gel-like coating.