This spring has been particularly good for two of our native butterflies that do not overwinter as adults and are a true sign of spring, the Orange-tip and the Holly Blue. This year, owing to the exceptionally warm spring, they both appeared earlier than normal and have been abundant on the allotments. I thought I would show a few photographs to illustrate the life cycle of the Orange-tip.
The Orange-tip is a species that can be seen along country lanes, hedgerows and woodland edges and the allotment drive and surrounds is a favourite place to see them. The male is especially attractive with orange tips to the forewings but the female upperwing resembles other species of white butterfly. The underwing is beautifully marbled, that provides good camouflage when, for example when the butterfly sits on plants like flowering Hedge Parsley.
The female lays her eggs just below the flower head most commonly on Garlic Mustard ( Alliaria petiolata) and Cuckooflower (Cardamine pratensis ) but also on garden plants such as Dame’s Violet(Hesperis matronalis) and Honesty (Lunaria arvensis). The egg is greenish yellow when first laid but changes as it matures to a beautiful orange colour just before hatching. This egg that I photographed was about 1 mm in length and is beautifully sculptured. There are some good stands of Garlic Mustard just inside the Flood Lane entrance, which is where I have found caterpillars.
The caterpillar when it first hatches eats its eggshell and also other unhatched eggs that are nearby. At first it is a brownish colour covered in warts, bristles and spines. The one below was just over 3 mm long. It has five stages or instars and in the latter stages is green, again with warts, with a horizontal white stripe along the sides. The caterpillars feed on the seed pods of the host plant and are cannibalistic. It is unusual to find more than one mature caterpillar per plant. When fully grown the caterpillar is about 25 mm long and can be difficult to spot when lying against the stem of the plant or on a seed pod.
The final moult is to the pupa that is either attached to the stem of the host plant or more commonly in nearby vegetation or on other vertical structures that provide a safe overwintering site.. The host plant often decays away in the winter. The pupa (chrysalis) is attached by a pad of silk at the rear end. Notice the delicate strand of silk attaching the waist to the stem and the wing venation visible through the skin.The butterfly spends eleven months of the year as a pupa before emerging the following spring.
The Holly Blue unlike the Orange-tip is double brooded and is a frequent visitor to gardens. The first brood on the wing from March/April and the second generation is on the wing in July and August. The first generation lays its eggs on Holly, the second on mature ivy, where it lays its eggs just below the ivy flower buds. the caterpillar then eats into the bud and feeds on the developing flower A good reason to retain some mature ivy on the allotments as a valuable food source for Holly Blue and other insects. The Holly Blue flies higher than the other species of blue butterfly and you can often see it skimming through trees or the tops of shrubs. The caterpillar drops to the ground to pupate in the surface leaf litter. Numbers of Holly Blue fluctuate enormously in numbers from year to year, over a six to seven year cycle of abundance and scarcity. This is thought to be in part caused by parasitism from a small wasp that lays its eggs in the caterpillars , with a single wasp eventually emerging from the Holly Blue pupa. The images show the upper and underwing. The female has broad blackish tips to the wing. The male has just a thin black margin.
All photographs © Bob Gomes