Green-veined White
Pieris napi
The thickened appearance of the main wing veins, with their smudge of dark dusting, should enable the observer to separate this species from the similar Large and Small Whites. There is variation in the strength of these markings and some individuals are almost pure white and lack the black wing spots altogether.
First brood adults tend to have darker veins than those from later broods, but have less black on their wings. The caterpillars are similar in appearance to those of Small White, but lack the yellow line running along each side. Instead, they have yellow rings around each of the spiracles.
The Green-veined White is not a pest of cultivated vegetables but uses a number of crucifer species for egg laying, with garlic mustard, hedge garlic and cuckoo flower most often selected. Nasturtium and alyssum may sometimes be used in gardens. The eggs are usually deposited on the undersides of leaves on small plants and hatch after 1-2 weeks. Once fully grown, the caterpillars leave the food plant and move away to pupate hidden amongst the surrounding vegetation. Individuals from the second brood (and third if it occurs) overwinter as pupae and result in the adults emerging the following spring.
Information from the ‘Butterfly Monitoring Scheme’ has revealed that the spring emergence of Green-veined Whites is now significantly earlier in the year than it was when the scheme began in 1976. In addition, the butterfly appears to be on the wing for longer. Both of these phenomena are likely to be linked to higher spring and summer temperatures in recent decades. It must be noted, however, that a hot dry summer can lead to a reduction in the size of the Green-veined White population the following year, a reflection perhaps of its preference for damp or humid conditions. This is the most widespread butterfly in Britain and Ireland and it currently has a stable population trend.
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