Naturalist

What’s happening to our butterflies and moths?

We can now look forward to brighter, warmer days, heralded by the early ‘yellow’ flowers such as daffodils, celandines, and primroses that precede the ‘red, white and blue’ of the late spring hedgerows. Continuing the yellow theme, one of the earliest butterflies usually first seen in February or March in gardens or hedgerows is the unmistakable sulphur-yellow Brimstone - the original ’butter-coloured fly’. As soon as they emerge, male Brimstones, which are much brighter yellow than the females, are on the hunt for females to mate. Mating occurs only in spring and the bottle-shaped eggs are laid in May or June on the underside of the food plant, alder buckthorn (widespread in Devon), or buckthorn. Larvae are found in June and July and the adults emerge in August and start preparing for hibernation. In summer and autumn, the adults take nectar from thistles, knapweeds and buddleia, and in gardens they feed on the flowers of runner beans and sweet peas. At night the butterfly rests under a leaf, with its wings together, looking just like a yellowing leaf. Brimstones are probably the UK’s longest-living butterfly, living for 10 or 11 months. They overwinter as adults in dense clumps of ivy, holly or bramble and emerge in early spring. Their distribution continues to expand northwards to the Pennines and North East England, probably driven by climate change.

The results of last year’s ‘Big Butterfly Count’, run by Butterfly Conservation, revealed further declines in Peacock and Small Tortoiseshell, but increases for Marbled White and Ringlet. They also showed the lowest-ever number of butterflies since the survey began. Does this serious decline worry you? If not, it should. Just like the canary down the coal mine, if it dies we know that something is wrong. Declining numbers of butterflies and other insects should ring alarm bells, not least because many of them are pollinators. Could the recent decline in swifts, which feed exclusively on aerial insects, perhaps be due to fewer insects? Over 50 moths have colonized Britain this century, mainly European species moving north, but some have arrived through the importation of exotic plants from abroad. A report by Butterfly Conservation on ‘The state of Britain’s larger moths 2021’ revealed that the abundance of moths decreased by a third over the last 50 years, and that this was greater in the southern half of Britain than in the northern half. We are all familiar with moths being drawn to light, including coming into houses in the summer. They are also attracted to streetlights which are found nearly everywhere in urban and suburban Britain. However, a study last year in southern England on the effects of streetlights on moths, found that areas with streetlights reduce the abundance of moth caterpillars in grass verges by a third, and in hedgerows by a half, compared with similar nearby unlit habitat.

Anthony John

For more information and ways you can help save butterflies and moths, visit butterfly-conservation.org