Orange tip butterfly icon of season

ONE of the great pleasures of a warm and sunny spring is seeing butterflies on the wing.

One of my favourite early season species is the orange tip.

I’ve been travelling on my boat recently and the canal banks are a sort of linear nature reserve, alive with spring flowers and butterflies. The new growth is visible in the water too because if you look down into the murky depths you can see the ghostly green shapes of water lily pads thrusting up from the canal bed, reaching for the sunlight. But it’s the orange tip butterflies dancing in the air that are the icons of the season.

It’s only the males that have the bright orange tips to the fore-wings and these hatch out in April or May and make themselves very obvious by ‘patrolling’ their territory. They fly backwards and forwards about a metre above the ground, often following the line of a hedgerow, a woodland edge or the bank of a river or canal. What they are doing, of course, is looking for a female.

These hatch out a few days later. They are slightly larger and have a black edge to their forewings. They also tend to have a dusting or flush of yellow on their bodies. This only occurs in Irish orange tip butterflies and, for this reason, they are considered a separate sub-species, Anthocharis cardamines subspecies hibernica. They feed on nectar and, while I’ve seen them taking this from garden flowers, their preference in the wild is for the delicate mauve flowers of lady’s smock, also called cuckoo flower. This is a plant of wet meadows and river banks so orange-tips, although they’re common and widely distributed butterflies, are mostly found in damp parts of the countryside.

The preferred nectar plant of the adults is also the favourite food plant for the caterpillars, which is quite unusual among butterflies. In most species there is a separate plant, or range of plants, supplying food to the adults and the larvae.

But orange tips can be flexible in their choice of larval food plants in the same way that the adults are flexible in their choice of nectar plants. The caterpillars are sometimes found on garlic mustard and, in gardens, on dame’s violet.

The mated females lay very large and conspicuous eggs on the flower head. They are orange and bottle shaped. The females try very hard to ensure that one egg is laid on each stem. But sometimes they make a mistake or another female comes and uses the same stem.

These mistakes end in disaster because orange tip caterpillars are cannibals. Each one needs a whole plant, or a whole stem of a larger plant, to support its voracious appetite and allow it to grow and form a chrysalis or pupa. So it destroys any potential rivals.

When the caterpillars first hatch out they are beige coloured with a black stubble. But as they grow they lose the stubble and turn green, with distinctive frosty flanks. They start by eating the flower head they were hatched on, then they proceed to the leaves and, if this isn’t sufficient, they’ll even eat the stalks.

Eventually they pupate, usually towards the end of June. The chrysalis is bright green with a faint white stripe and attached to a plant stalk by silken threads and a silk pad. Most will hatch into winged adults the following April or May, if they’re not discovered and eaten by birds or other predators. But a percentage of the pupae, usually between 15% and 20%, will over-winter for a second year. This is an evolutionary adaptation by an early season butterfly to guard against a very bad spring exterminating the entire population.

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