The Blue Butterflies

There are few things more uplifting than the sight of a bright yellow brimstone butterfly winging its way across the garden on the first sunny day of spring, or a red admiral in the late summer, feeding on Buddleia or sunning itself on a sheltered leaf.   But my favourite butterflies are the family of blues, with wings that shine like little jewels as they flash past or sit in the sunshine on a blade of long grass.  You are most likely to see the first common blues in gardens in late May, whereas earlier in the year, the holly blue is more apparent.  This family of butterflies technically includes the hairstreaks and coppers and many people find them very confusing, especially as amongst the blue species the females may be brown.  However, with a bit of help from a good identification guide there are ways of recognising these beautiful insects and by growing the right plants for them, some species can even be encouraged to your garden. 

There are eight species of blue butterfly in this country but rather few find our gardens amenable, due to their complicated life cycles and adaptation to specialised habitats.  Some species need ant colonies to be present in the soil, and the caterpillars have a highly specialised association with these creatures.  The common blue however is quite an adaptable butterfly and relatively easy to entice to your garden if you have some meadow grass and its main larval (caterpillar) food plant – the lovely bird’s foot trefoil.  The male common blue has bright blue upper sides to the wings, edged by a thin black line and a white margin.  His female counterpart however is usually dull brown, or brown with blue suffused through the upper wings and she has small orange spots around the wing margins.  Both male and female are beautiful insects, their under wings being silvery grey with black centred white spots.  The female also has orange markings, known as lunules, on the undersides of her wings - these are highly visible when the insects are feeding on flowers with their wings closed or ‘roosting’, usually upside down on grass stems, in the evening.

The common blue usually has two broods a year, and after mating in June, eggs are laid on the leaves of bird’s foot trefoil or black medick.  The tiny caterpillars are green and rather slug shaped, and they eat their way through the leaves until they are ready to pupate.  The pupa stays at ground level and hatches at the end of July to produce the new brood of late summer adult butterflies.   These mate and lay their eggs, but the tiny caterpillars feed only for a short while and then spend the winter months deep at the base of grasses and other vegetation until the spring, when they start to feed again, before pupating and hatching the following June.

The other blue butterfly commonly seen in our gardens, especially older country or suburban plots, is the holly blue.  If you find the blues confusing to identify, timing here is useful.   Any blue butterfly in your garden in April or early May is likely to be a holly blue.  This strong flying little butterfly is found only in the south of the country and is most likely to be seen in your garden if you have holly and ivy, its two larval food plants, nearby.  It is a species that has good and bad years in terms of its numbers, and this natural cycle is thought to come about as a result of the presence of a parasitic wasp, which preys on the holly blue caterpillars.  There are two broods each year, and the first holly blues are generally seen in April.  These mate and lay their eggs on the tiny developing flowers of holly or occasionally the native shrub dogwood, which the caterpillars then eat.  After pupation a second brood appears in July and August.  These adults lay their eggs on the flowers of mature ivy and the tiny bright blue butterflies can sometimes be seen flying high up around the tops of walls where the ivy flowers are situated.  The caterpillars that result from this brood pupate and spend the winter in this state, ready to emerge in the spring sunshine.  Holly blues take nectar from rather limited sources, but marjoram and forget-me-not are useful, as are the flowers of ivy.  Holly blue can be confused with the common blue, but unlike that species has fewer markings on the undersides of the wings, which are pale blue with small black spots.  The females also have a dark margin to their wings.

Some gardens in the south may have the occasional brown argus butterfly.  Another member of the blue family, this tiny butterfly looks remarkably like the brown form of the female common blue, and I find it extremely difficult to tell them apart.  Brown argus generally lay their eggs on the wild rockrose, but in my previous garden chose the small dove’s foot cranesbill as an alternative larval food plant.  This butterfly also takes its nectar from wild marjoram, a must-have plant in any butterfly garden.  Another member of this family is the small copper, a stunning little bright orange butterfly that lays its eggs on sorrel.  Again wild marjoram will tempt it to feed as will water mint on a pond margin.

A few years ago a group of refugees from Eastern Europe – all keen gardeners - visited my wildlife garden in Oxfordshire.  Whilst acknowledging the value of gardening for all manner of reasons, and delighting in my vegetable patch, they could see no reason what so ever to garden for wildlife.  ‘What use’ they asked ‘are butterflies’ looking at the wildflower meadow areas?  Surely the garden could have been put to better use if more food was grown there?  A valid question, and to justify my passion for wildlife gardening, after some rapid thinking, I replied that butterflies were good for the soul, and my comment was met with some thoughtful nods and murmurs of understanding.  For me this group of delicate, colourful butterflies makes wildlife gardening worth all the effort.

Attracting the Common Blue.  This species is the easiest of the blue butterflies to attract to gardens, and you can encourage them by dedicating a small area of the garden especially to them. Choose a sunny spot either to sow a small area of native meadow grasses, or allow an area of fine lawn (not rye grass) to remain uncut through the summer months. Using a trowel or bulb planter, remove small areas of turf and add small plants of bird’s foot trefoil in either spring or autumn.  These can easily be grown from seed in a peat free compost and pricked out into small pots when they are large enough to handle.  The area should be allowed to grow up uncut from March until September – the male blues love the long grass for sunning themselves during the daytime and for roosting in the evenings.  After cutting to a height of 5 to 10 centimetres in September, carefully rake off the cut grass with a spring rake, taking care not to trample about unduly – remember that those tiny caterpillars could be down at soil level where they will remain until the following spring.  Leave the area completely undisturbed throughout the winter.  A few of the adults’ favourite nectar plants including cornflower and wild marjoram somewhere near by, will also help to establish a colony of this beautiful butterfly in your garden.

© Text and photographs Jenny Steel 2017