Look Out For Glanville Fritillary Caterpillars in the Touraine Loire Valley

For butterflies to survive the winter they have to hibernate, or at least seek protection. A few, like Red Admirals and Peacocks, hibernate as adults, clinging to walls inside barns and garden sheds and hoping not to freeze. Some hibernate as eggs, hidden deep within the larval food plant, and others as pupae, ready to hatch at the first hint of nice weather in the new year.

A few don't actually hibernate, but spend the winter as caterpillars. When it's warm enough they munch their way through a leaf or two, but if it gets very cold they go dormant until the freeze is over. Of course, they don't go about in the open in the middle of winter. They huddle together in groups, protected by leaves and a web which they produce to keep the cold and predators out.

Glanville Fritillary caterpillars live communally when they are young, building a web which serves as a shelter from the cold and wet of winter at the base of their food plant. They will sallie out on all but the coldest days to eat and by the spring they will have gone from 10mm long to about 40mm and be ready for the transformation into adult butterflies.

The orchard has a plentiful supply of both ribwort plantain Plantago lanceolata and Persian speedwell Veronica persica. Being open and south facing this suits Glanville Fritillary butterflies Melitaea cinxia (la Mélitée du plantain in French) very well if the timing of the mowing has been right and the grass is not too long. They are also badly affected if the preceeding spring was dry.

Some years the orchard is home to a satisfyingly numerous population of Glanville Fritillary butterflies. In March and April I have to be careful not to tread on the caterpillars as they munch their way through the speedwell or plantain. Other years there may be very few, or even none, which is a worry, as it takes the species some years to bounce back and recolonise an area. Surprisingly, they are apparently not very mobile and stay within a very small radius of where they were hatched.

Glanville Fritillaries produce two generations a year and lay their eggs in clusters on the underside of Plantain leaves, where the caterpillars hatch out and live communally in their homespun silk nest. When the caterpillars are mature they are red headed, but young caterpillars are pale ochre with dark heads. The young ones greatly resemble the plantain flowers in the spring. The species seems to benefit from traditional agricultural practices, as the nests are often found in fallow land and along rural tracks where the roadside vegetation is full of plantain.

Adult males often sit with open wings on these dirt tracks, or on the tips of grass seed heads. They are assertive, agile and rapid flyers, and quite agressive to one another.