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Published in an April issue of Organic Gardening Magazine

May is wonderful month in the garden – full of the promise of summer but still with the green lushness of spring.  In the countryside and the wildlife garden, the breeding activity of some birds and small mammals may be coming to an end but many of our butterfly species are still in the throws of mating and laying eggs.  May is an intermediate month for butterflies with both spring and summer species around.   If your garden is butterfly friendly with plenty of nectar and larval food plants to attract these insects, you could see a good variety this month including the spring species such as orange tip and brimstone, together with the first of the summer butterflies, including common blue and small copper.

Our native butterflies have varying strategies to help them through the winter months.  The brimstone hibernates as an adult insect deep in vegetation, ready to fly as soon as the sun shines in March or even February.  Small tortoiseshell, another of the early fliers, over-winters in garages and sheds or under loose bark on fence posts or logs.  Others species, such as the large and small whites, spend the winter as pupae, safe from the worst of the weather, and the common blue survives the cold conditions as a tiny caterpillar sheltering deep in ground level vegetation.  The whites will emerge as fully-fledged adults in April or May while the common blue larva will complete its transformation in May or early June.  However, other butterfly species that appear in our gardens this month have not spent the winter here at all, but reach us in late spring having flown across the Continent, an extraordinary fact that many people find quite amazing.  We are used to the idea that birds migrate between countries, often over vast distances, but few of us appreciate that insects also perform these feats of endurance – especially butterflies and moths.  Our winters are too cold for these migrant species and sadly, once here, few return to the Continent or North Africa.  However, while they are here, they produce another generation of butterflies to grace both our gardens and our countryside.

The red admiral is one of our most recognisable butterflies, its stunning pattern of red, black and white making it a firm favourite with many people.  A few individuals of this species do spend the winter here in hibernation, and others migrate in the autumn back across the Channel to Europe (they are sometimes seen from cross Channel ferries!) but by and large they are unable to survive our varying winter conditions except in the warm Southwest.  In its Central Europe home, this butterfly hibernates where winter temperatures are consistently very cold whereas many insects that hibernate in the British Isles are fooled into untimely emergence when temperatures fluctuate early in the year.  A few warm days in February are enough to waken a red admiral, but this early emergence usually spells disaster.  With no nectar available and fat reserves used up, the survival of these individuals is doubtful.  February mild spells are often followed by harsh weather, which finishes off many butterflies that have emerged early from hibernation. 

If the conditions are good we should also see another migrant species this month.  The painted lady is a butterfly that is unable to over-winter at all here.  It simply does not have a hibernation stage in its life cycle, relying on a continuous succession of breeding in North Africa and Arabia where it is resident.  However, large numbers of this insect can reach our shores in some years, especially if the weather conditions and prevailing winds are favourable.  1996 was an amazing ‘painted lady year’ when it was just about the most common butterfly around.  Huge numbers of this butterfly arrived on our shores in May and June and moved northwards throughout the country, dominating Buddleias and other favourite nectar plants such as thistles and the wild field scabious.  Unfortunately some years are very poor for the painted lady, as the weather conditions simply do not suit its requirements, but we never know until migration starts just what sort of influx there might be.

On arrival on our shores in late spring, painted ladies seek out thistles, their preferred larval food plant, on which to lay their eggs.  Nettles will also be used - these are also the larval food plant of red admiral, small tortoiseshell and sometimes the comma.  Fortunately there is generally no shortage of these plants on farmland and roadsides.  This means that the painted lady has plenty of opportunities to breed and in good years there can be huge ‘home-grown’ numbers of this beautiful butterfly.  The caterpillars are much like those of the red admiral being black and spiny, and they also produce a tent of leaves in which to shelter.  After pupation these butterflies emerge in the summer months to feed on Buddleia.  They also enjoy the nectar from scabious and statice.  Sadly the majority of these individuals perish unless weather conditions enable them to make the long journey back to Europe and North Africa.

Throughout the summer other butterflies along with these two species migrate across the Channel to our shores.  The bad news for those amongst us who grow Brassicas, is that the large white is one of these travelling insects.  They too can arrive in the summer in large numbers, boosting our homebred insects.  Rather less problematic is the wonderful clouded yellow, a bright butterfly that again can produce massive influxes of individuals.  Migrant moths are also very common, although less often seen by most of us.  Only the day-flying hummingbird hawk moth regularly reveals itself to observant gardeners, feeding on tobacco plants, phlox and honeysuckle but others such as the huge    also appear from time to time.

The phenomenon of insect migration means that some species of butterfly are a great deal more mobile than we might realise.  This is good news for those of us who like seeing these insects in our gardens – their mobility means that there is always a chance of catching a glimpse of a rare clouded yellow, or seeing a group of red admirals feeding on fallen plums beneath a tree.