The Small White Butterfly (Pieris rapae) is also known as a cabbage butterfly because their caterpillars feed on brassicas.
They are common throughout the UK, Europe and also large parts of the sub-tropical world.
In Britain they are double brooded, and can be seen flying between March and October.
The males generally have a single black spot on the upper surface of the forewing and two on the underside. The females have two black spots on both sides of the forewings.
Butterflies may often be seen nectaring on a wide variety of flowers, including buddleia, dandelions and the purple heads of knapweed. Their favourite foodplants are from the brassica family – cabbages of all kinds!
Eggs are laid singly by the female during the day on the underside of brassicas, wild and cultivated crucifers and Nasturtiums. The cone shaped eggs are pale at first but soon turn yellower. Despite being only 1mm high they are still quite easily spotted against the green leaves of the larval food plant. The eggs hatch within 3-10 days depending on temperature.
The caterpillars of the Small White are 2mm long and pale yellow with ochreous heads when first hatching. They turn progressively greener with each instar and when fully grown, after 3 weeks, are 25mm long with a green head and body that are covered in short white hairs. A faint yellow dorsal line and a broken row of yellow marks following the spiracular line are key identification markings. (Wildlife Insight)
For more information on the Small White, see the Butterfly Conservation website.