Animals life cycles

Chapter three

Other Invertebrates

There are many other groups of invertebrate, and they all have very different life cycles. Did you know that earthworms, octopuses, spiders, and lobsters are all invertebrates?

Earthworms

All earthworms lay eggs, because they are hermaphrodites. This means that they all have male parts that produce sperm and female parts that produce eggs, but they cannot fertilize their own eggs. After earthworms mate, their bodies make special rings with eggs inside. The ring moves forward over the worm's body and then it comes off. Then the ends of the ring join together. The eggs hatch after about three months, and young earthworms can mate when they are 12 months old.
Octopuses

Baby octopuses live in the open ocean at first, but when they grow, they move down to the bottom of the ocean. Here they live on their own in dens.

Octopuses are ready to mate when they are one or two years old. Some female octopuses lay about 200,000 eggs, and many put them in strings from the top of their dens. The females keep the eggs safe from predators and they carefully push water over them so that they get enough oxygen. The octopuses do not eat for up to ten months when they are caring for their eggs. After the eggs hatch, the female octopuses die.

Spiders

Spiders produce silk, and they use it to make webs, where they catch flies and other insects. Most species of spider also put lots of silk around their eggs to make a special cover, called a cocoon.

Most spider eggs hatch after a few days or weeks. The baby spiders, or spider lings, grow fast and they molt a few times. They can soon make their own webs and catch their own food.

Many spiders die after they lay their eggs. Some spider lings eat their mother's body after she dies!

Lobsters

A female lobster can lay up to 10,000 eggs, but only about ten of them will live. The female lobster carries her eggs hidden under her tail for almost a year. When they are ready to hatch, she lifts her tail and they float away.

When the eggs hatch, the larvae move to the top of the ocean. Life here is very dangerous because of predators and difficult currents. Lobster larvae look very different from adult lobsters. When they are about one month old, the larvae move to the bottom of the ocean. They molt about 25 times before they become adults.

Lobsters often eat their old shell after molting. This helps their new shell to become hard.