Wildlife with an amateur observer
AUGUST has seen a influx of beautiful migrants butterflies to the coast of West Cork with one species in particular – the painted lady – appearing in large numbers.
They’ve come here as refugees from the heat waves in Britain and Europe this summer where their host plants have suffered through drought.
In the northern and western coastal regions of Ireland painted ladies are being seen in even greater numbers with hundreds, and perhaps thousands of them, coming in over the water in clouds of fluttering wings.
Painted ladies have occasionally come to Ireland in such massive migrations in the past, perhaps once in a decade, but it seems that this phenomenon is happening more frequently in recent years.
The painted lady is the most widely distributed butterfly in the world, found on all continents except Antarctica and Australia, giving rise to its alternative name of the ‘cosmopolitan’ or ‘cosmopolite’ butterfly.
It’s a long-distance migrant that spreads northwards each year in sometimes spectacular migrations. It arrives in varying numbers to Ireland most years and breeds here in the warm summer months.
Some years it arrives in huge numbers, as is happening this year, but other years sightings of the painted lady can be few and far between. It can sometimes come here in winter too but this is rare although I did see a good number in this locality in February this year.
This is a butterfly that can migrate long distances, covering up to 100 miles a day in speeds of up to 30 MPH, flying at an altitude of around 500m.
How migrating butterflies find their way is not yet fully understood, although there is some evidence that they can navigate by the position of the sun and make adjustments for the wind’s direction and speed.
However, like birds, butterfly migrants can be temporarily swept off their normal path by abnormally windy weather. This results in butterflies turning up in unexpected places and the large numbers seen recently in Donegal and Scotland might be as a result of this.
Why such large-scale migrations happen in some years and not others is a result of conditions elsewhere, for example this year’s heat waves in Europe. But massive population accumulations can also kick off mass movements to travel in search of food and an opportunity to breed in better conditions.
Breeding in Ireland
While painted lady butterflies can be seen feeding in a wide range of habitats, the places where they can breed are more restricted. The females deposit their eggs primarily on thistles but occasionally will use nettles and other plants.
Their green eggs are laid singly and once emerged from the egg, each spiny greyish-coloured painted lady caterpillar spins silk to draw together a leaf and then feeds concealed within this shelter.
When fully grown, the caterpillars form ‘tents’ by spinning the surrounding leaves together and change into chrysalids spangled with silver or gold. The adult butterfly emerges about two weeks later with lovely pink tinges to its wings which quickly fade. The adult stage only lasts around 2 weeks so the whole life-cycle of this long-distance traveller is just over a month.
Until comparatively recently, it was assumed that when the weather got colder these Irish-born butterflies died. However, now there is evidence that many of the offspring – not the original immigrant adults – fly back south to warmer countries where they breed to ensure the survival of the species.
The painted lady is not the only butterfly to do this as red admirals also migrate southwards after breeding in Ireland. Some red admirals over-winter in Ireland too but a very cold winter could wipe out this population so the adults that migrate southwards help to ensure the survival of the species.
This is the third year in a row that significant numbers of painted ladies have come to Ireland, bucking the trend of years’ past when such influxes were a once-in-a-decade phenomenon.
This may be as a result of climate change or even species evolution or it could be a statistical anomaly. However, these events are important to record and you can submit sightings to the National Biodiversity Centre on its website www.biodiversityireland.ie (a very simple process) or by emailing them to Butterfly Conservation Ireland on [email protected]