Visiting fritillary draws the crowds

There have been some very interesting reports over recent weeks of butterflies not often seen in our region. Some of these, like clouded yellow and camberwell beauty, are immigrants from the Continent, while others probably originate from closer to home. One particular individual, a silver-washed fritillary, put in an appearance at Natural Surroundings, near Holt, and attracted quite a crowd when its presence was put out on the pagers used by many Norfolk birdwatchers. (The middle of the summer is often a quiet time bird-wise and, in response, many birdwatchers take up a passing interest in butterflies and dragonflies). Given that this particular species of fritillary effectively became extinct in our region several decades ago, and that it is similar in appearance to the dark green fritillary (which does breed in Norfolk), there was understandable controversy as to whether this was simply a case of mistaken identity. In the event, the fritillary was well-watched by at least some observers capable of distinguishing the two species and its arrival occurred at a time when several other individuals were seen in Cambridgeshire and Suffolk. This species is largely restricted to the south and southwest of Britain and, with a powerful flight, it is considerably more mobile than our other fritillaries. During particularly hot summers individuals may be seen well away from the core range – a pattern matched by the butterfly’s response to climatic trends. The population has been shown to expand during warmer periods and contract during cooler ones.

Although I did not make the trip to see the silver-washed fritillary at Natural Surroundings, I did visit two of our dark green fritillary colonies this year, first at Winterton Dunes and then two weeks later at Holkham. Although a species of downs and grassland over much of its core range, the dark green fritillary seems to do very well on coastal sites, either on dunes or on undercliffs. Here the males spend much of the day on the wing, searching for females, and the patrolling flights are characterised by short bursts of rapid wing beats followed by periods of gliding. The females themselves perch low down in the vegetation and the males probably locate them by scent. Once mated, the female will return to perch within the vegetation, soaking up the sun’s warmth to help her eggs ripen. As such, although these butterflies are easy to spot when on the wing, they are difficult to photograph, except during the early morning and late afternoon when nectaring. A late July or early August visit to Winterton Dunes should guarantee views of dark green fritillaries and may just produce a clouded yellow or even a camberwell beauty.

HIbernating butterflies

Although winter can be a difficult time, there are species that manage to avoid the worst of its ravages by going into hibernation. Many are familiar to us: newts that retreat into the spaces under log piles, hedgehogs that bury themselves in last autumn’s leaves or ladybirds that squeeze into the cracks of a window frame. Most of these creatures will spend the winter unnoticed by homeowners and gardeners, but others may be chanced upon as logs are brought in from the woodpile or something is fetched from the garden shed.

This winter, a small tortoiseshell butterfly has chosen my shed and it is interesting that this butterfly should choose to overwinter as an adult. Very few of our resident butterflies overwinter as adults; the majority spend the winter as caterpillars, although nine species overwinter as eggs and eleven as pupae. It is also interesting to note that, with the exception of the speckled wood, the hibernating phase is always the same in a given species. The speckled wood can hibernate as either a caterpillar or a pupa. Along with the small tortoiseshell, the other species to overwinter as adults are comma, peacock and brimstone. To these can be added large tortoiseshell (though now thought to be extinct as a resident species), red admiral (though only in the extreme south of the country does overwintering appear to be successful) and Camberwell beauty (which overwinters occasionally). Many of these species will spend the winter in hollow trees or outbuildings but the beautifully camouflaged comma prefers to overwinter on exposed branches or among dead leaves and the brimstone hibernates deep within an evergreen shrub. During hibernation these butterflies must be vulnerable to predation by birds and this may be why many have evolved their camouflaged underwings. The peacock goes a step further and has evolved a warning display. If disturbed, the peacock will open its wings to their fullest extent to reveal the large ‘owl-like eye’ pattern on its wings. At the same time it produces a hissing sound by rubbing its wings together, something that is usually enough to scare off a would-be predator.

Once we receive a run of several days of warm, spring-like, weather many of the butterflies will emerge from hibernation to seek out nectar sources to replenish reserves lost over winter. None of the species is able to mate immediately on waking but needs to feed and bask in the sun to develop the eggs or sperm needed for the reproductive act. The butterfly can always re-enter hibernation if spring has not really arrived, although it will have lost vital reserves and be less likely to survive the remaining winter period.