These are the caterpillar of the Cabbage White butterfly. They are great eating machines and have been living on the underside of the cabbage leaves in our school garden.
The larger ones look ready to pupate but you will have to read Katie's post to find out their fate.
The Peacock butterfly lays her eggs on the underside of a stinging nettle.When the caterpillars emerge they are highly conspicuous. In order to protect themselves from predators they cover themselves in a type of web. If you look carefully at this picture you will see tiny caterpillars feeding inside a type of web. When they have eaten all the nettle inside the web they move on to another part of the nettle.
These caterpillars are much larger, are jet black in colour and their bodies are covered in tiny spikes. They moult several times as they outgrow their skins. On the right of the picture you can see the remains of their protective web.
Click here to see some of the beautiful pictures that he took of the Marsh Fritillary. Be sure to scroll down to the bottom of the page so that you can see a mass of butterfly eggs on the underside of a leaf.