Small White Pieris rapae (Linnaeus 1758)
Family: Pieridae, subgroup Pierinae (The Whites)
Photos above and header by Martin Partridge
Photo above left and header show a male
Photo above right shows a female (two black spots just about visible on top of forewing)
The Small white, also sometimes called a Cabbage White, is one of Yorkshire’s most common butterflies. It is white with grey to black wing tips.
It is easily confused with the Large White and, just to add to the confusion, the Large White isn’t always bigger. The Small White has smaller paler dark wing tip patches, which don't curve far round the wing.
It can also be mixed up with the Green-veined White but the Green-veined White has clear veining on the underside of the wings.
Summer generation Small Whites are larger than the spring brood and just about overlap in size with smaller Large Whites. The first brood is paler than the second and first brood male wing tips can be very pale, almost lacking in colour. Female Small Whites are more strongly marked than males, with two spots on each upperside forewing compared to the males’ single spot.
This species is found in most Yorkshire habitats, especially farmland, gardens and allotments where cabbages and related crops are grown because these are the main larval food plants. Nasturtiums (Tropaeoleum majus) are also a popular foodplant. The Small White will also lay eggs on wild cabbage species and can live and breed in almost any habitat which is part of the reason it is so successful.
Populations tend to be thinner in higher areas where it often gives way to the Green-veined White though the ratio of the two species on higher ground varies a great deal from year to year.
Although the Small White can be a pest it is also an important part of the ecological system in our gardens and countryside in that it provides a food supply for many other creatures; for example, the House Sparrow, which eats both eggs and larvae. Larvae are also taken by Song Thrushes and Titmice.
Small Whites are often one of the first of the non-hibernating species to be seen on the wing in spring and the last in autumn.
There are usually two broods, plus a partial third in warm autumns, which give the impression of a continuous flight season from March to October. The numbers of the second brood tend to be larger than the first, and in many years the second brood is also increased by immigrants.
It is a common species throughout the world and often a pest of cabbage and related crops.
There are usually two overlapping broods and often a partial third brood so there are continuous Small whites through the Spring and Summer. The first brood usually seen in March to May.
The eggs are laid singly, usually on the undersides of foodplant leaves which are chosen for warmth and shelter, with the result that farm cabbage crops may only be infested around the edges of fields. The females spend a lot of time choosing the leaves to lay on, going backwards and forwards over the alternatives.
The white eggs change to yellow, then grey, before straw-coloured larvae hatch out. These gradually become blue-green covered with tiny black dots and with a line of yellow dots along the sides.
Small Whites lack the Large White's protection of an unpleasant mustardy taste and are very attractive to birds. As protection they camouflage themselves by feeding singly along the central vein of leaves and stay very still. They don’t move around vigorously like Large White caterpillars. Larvae on cabbages usually burrow into the centre of the plant and cause a lot of damage.
Larvae are strongly attacked by harvest spiders and ground beetles as well as parasitic wasps such as Apanteles rubecula, plus virus diseases also take a toll, especially in cool, wet summers. The larval stage lasts about 20 days and passes through 5 moults.
First brood larvae may pupate on other foodplants, attached to a stem by a silken pad and girdle. Later broods tend to climb tree trunks, buildings and other structures in similar way to the Large White. Pupae are well disguised, varying in colour from green to brown, but they are still searched for and eaten by birds. Small Whites pass winter in the pupal stage and can react quickly to early spring warmth, occasionally even emerging during a midwinter mild spell.
Once emerged, Small Whites are very active and fly for a large part of the day.
Photos of single egg and final instar larvae (with early instar Large White caterpillar to right) by Catherine Jones
The species is not under threat.
Around 40 variations have been described with a very yellowish form ab nova Ter Haar, which in flight might be mistaken for a Pale Clouded Yellow. Occasionally females show the two upper forewing black spots joined up, forming a black bar: ab asciata Tutt. Morris (1853) pointed out that the black spots on the upperwings are very variable and no two specimens in his collection were the same.
With thanks to The Butterflies of Yorkshire edited by Howard M Frost
Catherine Jones 20/11/20