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Small White
Behaviour and Ecology Small Whites live in loose, open populations and can be found across a range of habitats. Females lay their eggs in the underside of leaves, usually (in gardens) on cultivated brassicas and nasturtiums. Each egg usually hatches within three to seven days and the resulting caterpillar then eats a small hole in the leaf before heading towards the heart of the plant. Here it will remain hidden for a week or so, growing in size, before moving back to feed on the leaves of the plant, hiding along the leaf mid-rib to avoid predators. The caterpillars suffer
from very high levels of predation when they are young and up to
two-thirds of those that hatch may be taken by predators like beetles
and harvestmen. Older caterpillars and chrysalises are often taken
by birds, especially tits and warblers, and it has been found that
Small Whites lack the range of toxins stored by Large Whites, something
that is likely to have an influence on the level of predation. There
are also parasites, notably the parasitic wasp Apanteles rubecula,
and various viruses, the latter being important during cold, wet
summers. Identification The Small White is most likely to be confused with the Green-veined White (especially those poorly marked individuals of either species). The best way to separate the two species is to look at the dark tips to the upper surface of the forewings and also to look for the dusting of scales along the veins (seen in Green-veined White). In Small White these dark wing tips end abruptly and do not gradually merge into the darkened wing veins seen in Green-veined White. Large White, as its name suggests, is a larger butterfly and has more strongly marked wing tips. Individual Small Whites usually show two small black spots on the forewing (visible from above and below) and a single black spot on the upperside of the hindwing. First brood males often lack the spots on the upperside of the forewings. Second brood individuals of both sexes are typically more strongly marked. The pale green caterpillar has a fine yellow dorsal stripe and a series of yellow spots along its side.
The use of gardens - results from Garden BirdWatch Following a mild winter, adults can be on the wing as early as February but the main emergence (they overwinter as a chrysalis) is in April. Numbers peak in May and then fall away in June. A second brood emerges from the end of June through into July. There may sometimes be a third brood late in the summer.
Small Whites prefer to feed on pale coloured flowers and so use a range of different species from those of the other familiar garden butterflies. There mobility often brings them into even urban gardens where they can be seen feeding throughout the summer.
Although widespread across Britain and Ireland, the species is less common in the north and west. Click here to see a map showing the distribution of Small Whites within gardens at the national level, as recorded by BTO/CJ Garden BirdWatchers during 2003.
Click here to see what the region codes on the above graph mean. |
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