Another Life: What to do if you disturb a butterfly’s winter slumber

A butterfly in January? We need something to encourage us. In the month for new year resolutions, here’s a thought for the natural world in its struggles to survive.

That lovely butterfly, the small tortoiseshell, really can turn up in mid-winter, disturbed from its hibernation in a fold of the spare room curtains, or tucked behind a picture or the dresser.

It will have picked its spot carefully in early autumn, counting on the camouflage of its dark underwings. But it can also reckon without the false signals of central heating. What do you do when it emerges to flutter at the lights or windows, keen to fly out to join the spring the house temperature says has come?

It depends how much you care. Just letting the butterfly out into the cold will see it collapse and soon be snatched up by a blackbird. But salvaging its winter sleep can also take quite an effort.

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In his blog on the Butterfly Conservation Ireland website, lepidopterist Jesmond Harding has offered ways to proceed. One is to tuck the butterfly into a tissue-lined tube and keep it in the fridge until March or April, or, once calmed by the cold immersion, leaving it somewhere safe to resume its slumber.

If the tortoiseshell is exhausted from too many flying circuits of the room, it may also need a reviving snack from a honey-soaked pad of cotton wool.

Harding is quite used to overwintering small tortoiseshells and feels “a burst of delight to watch the butterfly surge into the sunshine in spring”. It’s part of the 25 years of his study that distinguish a €35 quality paperback on sale from his home in Co Kildare.

The Irish Butterfly Book is definitive, engaging and heavy with glossy illustration. It covers the ecology, life-cycles and food plants of Ireland’s 35 butterfly species, many of them around Harding in the midlands and more in some 40 habitats from Cork to Donegal. The sites are mapped and photographed, along with their likely species.

It’s a book full of knowledge, from Harding’s own painstaking observation and also new lepidopteral research. Most people are content just to have a name for a butterfly, but his essays on each species open up fresh worlds of interest, observation and mystery. Butterflies, their caterpillars and chrysalises don’t lead such casual lives after all.

Why do some female speckled woods flaunt themselves at males while others fly evasively? Why do male brown hairstreaks ignore females after 11 am? Can brimstones really predict the weather? How do painted ladies manage to migrate south in autumn when we never see them go?

The ants may be attracted by the pupa's song, which is inaudible to humans

Butterflies are on the wing with one overriding purpose: to reproduce. In some species, the males shower females with scales from their wings that contain an aphrodisiac called androconia. In the green-veined white, its scent of lemon verbena, Harding reports, “is powerful, even to a human”.

The larvae and pupae of Ireland’s three blue butterflies – the small, common and holly blues – can seek protection from ants in return for a feed of sweetness.

“The ants,” writes Harding, “may also be attracted by the pupa’s song, which is inaudible to humans. The song may be caused by the pupa [or chrysalis] rubbing segments against each other, which summons the ants to lick sugary secretions that ooze from pores on the pupa.”

That curious but essential contract figured in research to save England’s last large blues, dependent on a single species of vulnerable ant. This last year has seen numbers of butterflies in the UK at an all-time low. Those of the small tortoiseshell dropped by a third, continuing a long decline. The peacock fared even worse, with its lowest count since 2012.

The differences in weather between Britain and Ireland are now marked by extremes of climate change, with the Atlantic still moderating our own extremes of heat and cold. As Biodiversity Ireland has reported, the populations of the 15 commonest butterflies have continued to grow from the lows of 2016. In 2020 the numbers of small tortoiseshells increased significantly as early fine weather resulted in a very large second generation.

Jesmond Harding agrees that the earlier springs and longer growing season will see some species emerging earlier and producing more generations. Among new butterfly colonists, warming could see the dramatic swallowtail arriving to breed on wild carrot and fennel.

He could add these to the plants he recommends for creating wildlife gardens, though the 18 species of butterfly attracted to his own might seem rewarding enough.

The Irish Butterfly Book is available from Butterfly House, Pagestown, Mulhussey, Co Kildare. Jesmond Harding’s email is jesmondmharding@gmail.com