White butterflies are much in evidence at this time of year. Most people know the familiar "Cabbage White", but in fact this is two species: Large White (Pieris brassicae), left, and Small White (Pieris rapae), right.
In appearance, the Large White can be identified by size, by more extensive black on the wing tips and in the female by two large black spots on the upper wing, which are absent in the male. The black on the wing tip of the Small White is often greyish and is confined to the extreme tip. The underwings of both species are plain pale yellow.
The Large White is common around vegetable gardens and it is the species that breeds on brassicas such as cabbages, Brussel sprouts, or nasturtiums. They lay their eggs in clumps of about 50 to 100 on the underside of leaves. Their caterpillars live communally and are greedy feeders able to quickly strip a plant of its leaves, so no wonder it is not popular with gardeners! The emerging caterpillars taste of mustard oil (a component of brassicas), which makes them unpalatable to predators. The Small White has similar habits and plant preferences, but lays its eggs singly, which makes it less of a nuisance. In addition, its caterpillar lives a solitary existence, although several may occur on one plant. It is not so poisonous as the Large White caterpillar so is subject to a lot of predation by birds and beetles. As well as cultivated brassicas it also uses wild Crucifers such as Lady's Smock, and can be found almost anywhere. Both these butterflies are partial migrants and their numbers are often increased by influxes from the Continent. Both species have two broods (sometimes three), and it is the second brood that are now on the wing.
There is also a third species, often overlooked because of its similarity to the Small White. The Green-veined White (left and right) is extremely common and gets its name from the veins on the underside of the rear wing, which are picked out in greyish green, and easy to notice when the butterfly is at rest. It has a preference for damp grassy areas or woodland rides and is very common, often visiting flowers. It lays its eggs on Crucifers such as water cress, lady's smock, hedge mustard, or garlic mustard, choosing seedlings over mature plants. The female tests the leaves of the plants by tapping on them with her feet (as do all the whites) in order to detect the mustard oil which Crucifers contain. If you see a small white butterfly it is definitely worth checking its underside to see if it is this species, and not a Small White.