Green-veined white (Pieris napi): identification, range and host plants

The green-veined white, Pieris napi, is a white butterfly of the family Pieridae, named for the dark scales that trace its wing veins on the underside. It is a circumboreal species, found across Europe and Asia, including the Indian subcontinent and Japan, plus the Maghreb and North America. Despite the resemblance to its relatives the small white and the large white, it keeps mostly to damper, shadier ground, and its caterpillars feed on wild crucifers rather than garden brassicas.

Identification

The green-veined white has a wingspan of 40 to 52 mm. The upperside is white or pale yellow-white with grey-black wingtips and, in later broods, a scattering of dark scales along the veins near the wing bases; the feature that gives the species its name shows best on the underside, where the veins of the hindwing and the forewing tip are overlaid with greenish-grey scales, giving a streaked, veined look quite unlike the plain white underside of the small white. The sexes differ in the markings on the forewing upperside: a female generally carries two black spots and a darker overall tone, while a male typically shows a single black spot or none at all, especially in the spring brood. Spring-brood adults are smaller and more lightly marked than those flying later in the season.

Range and habitat

Across its wide range the species favours damp, grassy places with some shade: forest edges, hedgerows, meadows and wooded river valleys, from sea level up to 3600 m. That preference for shelter and moisture keeps it in woodland rides and shaded hedgerows more than out in open fields.

Life cycle and host plants

Caterpillars feed on wild crucifers: hedge mustard, garlic mustard, cuckooflower, water-cress, charlock, large bitter-cress, wild cabbage and wild radish. The species rarely troubles cultivated cabbages, sticking instead to these wild relatives of the cabbage family. The species overwinters as a chrysalis, emerging as an adult the following spring.

Behaviour and flight period

The number of broods a year tracks latitude closely. In northern Europe there are typically two or three generations, flying from April to early September, while in southern Europe three or more broods overlap from March to October; across its full range the species produces 2 to 4 generations a year, depending on region and climate. Adults fly low and steadily over grass and hedgerow, visiting a wide range of flowers for nectar, and the lightly marked spring brood is often the first white butterfly of the year on the wing in shaded lanes and woodland edges.

Similar species

• Small white (Pieris rapae): shares much of the same range and food-plant family, but keeps to more open ground and lacks the dark-veined underside.
• Orange tip (Anthocharis cardamines): the female’s plain white-and-black forewing can be mistaken for a green-veined white at a glance, though she lacks the veined underside pattern.