Wednesday 17 January 2018

Caterpillars of the Large White the bane of vegetable gardeners

By Jim Hurley - Nature Trail

Caterpillars of the Large White butterfly.
Caterpillars of the Large White butterfly.

While the summer just past was generally poor for butterflies, the fine, settled weather at the end of August saw good numbers of these colourful insects on the wing. Particularly nice to see were the stunningly fresh Painted Ladies, these lovely migrant butterflies that erupt northwards each year from North Africa.

While butterfly numbers fluctuate each summer, one local resident that can be relied on to be present each year is the Large White, that bane of vegetable gardeners who attempt to grow good cabbages.

The name 'Large White' sums up this insect's identification pretty well: it is normally white in colour and is normally the largest of the small number of white butterflies that is resident in Ireland. The resident population is often boosted by the arrival of immigrants from abroad and these migrant Large Whites are said to be recognisable in that they are noticeably larger.

Small-sized Large Whites are difficult to identify in that they overlap in size with some other white butterflies. To add to the complications, Large Whites may also appear a bit yellowish in colour rather than pure white and the normally prominent black markings on the wings may be reduced or may even be entirely absent.

How butterflies got their name is unclear. One interpretation is that the insects were named after sulphur-yellow relations of the Large White that were originally known as the 'butter-coloured flies' or butter-flies.

Anyway, back to the Large White. The insect is associated with people and is therefore uncommon in remote rural areas, up mountains and in wetlands. It thrives where people are cultivating the crops that its caterpillars like to eat like Cabbage in gardens and Oil-seed Rape in farmland.

To protect their crops from the ravages of hungry caterpillars, gardeners and farmers spray insecticides to poison the unwanted pests. These chemicals obviously take a toll on other insects and the collateral damage adds to the overall decline in biodiversity associated with intensive crop production.

The Large White overwinters as a pupa or chrysalis hanging on a silken thread under a window sill, shed roof, tree trunk, fence post or other such place. Adult butterflies emerge from these pupae or chrysalises in April and May. The adults breed and the females lay eggs that hatch within a week to produce the familiar eating machines that are the caterpillars.

Second-brood caterpillars are still munching away on greenery and will continue to do so until the advance of autumn forces them to pupate.

Wexford People

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