In late spring Cornwall, the Common Blue butterfly dances over golden Bird’s-foot Trefoil on sunlit clifftops. Their life cycles are perfectly in step, with two strong broods and, in rare warm autumns, a third — a timeless coastal partnership shaped by Cornwall’s mild climate.
On a still May morning, when the breeze off the Atlantic is no more than a sigh, Cornwall’s clifftop grasslands come alive with flashes of bright, iridescent blue. The Common Blue butterfly (Polyommatus icarus), smaller than most of Britain’s blues yet striking in the sun, drifts low over the turf. Males shimmer with a pure sky-blue glow edged in black and white, while females, usually brown with hints of blue dusting, bring a subtler beauty to the scene.
Here, on these exposed slopes and sheltered headlands, they share a long and ancient partnership with one of Cornwall’s most unassuming yet vital wildflowers — Bird’s-foot Trefoil (Lotus corniculatus). Together, they create one of the most reliable signs that late spring has truly taken hold.
Cornwall’s coastal grasslands are perfectly tuned to the needs of the Common Blue. Short, flower-rich turf, maintained by wind, salt spray, and the quiet work of rabbits grazing the sward, keeps the ground open for wildflowers. Bird’s-foot Trefoil thrives in these conditions, forming dense, low mats sprinkled with golden flowers. The sight of them carpeting a clifftop in May is as much a part of Cornwall’s seasonal rhythm as thrift in the rock crevices or gannets diving offshore.
These grasslands are warm, sunny, and often south-facing — a combination that creates gentle microclimates where butterflies can bask, feed, and court. The open spaces and low-growing plants allow the sun’s warmth to reach the soil, benefiting both the butterflies and their foodplants.
For the Common Blue, Bird’s-foot Trefoil is more than just a nectar source — it is the cradle of the next generation. Females lay eggs singly on the young shoots or in the leaf axils, carefully choosing spots where fresh foliage will be ready for the hatching caterpillars.
In Cornwall, second broods are the norm, often emerging strongly in July or early August, with the first brood taking flight in May. In very warm autumns, a partial third brood can occur — rare, but a reminder of how climate and geography can stretch the season.
Caterpillars feed on trefoil leaves for around three to four weeks before pupating in the grass. Those from the final brood of the year spend the winter as larvae, tucked low in the vegetation, ready to continue their cycle in spring.
While Bird’s-foot Trefoil is the mainstay, adult Common Blues are not exclusive in their tastes. On coastal slopes they often visit kidney vetch, selfheal (Prunella vulgaris), wild thyme (Thymus polytrichus), and various clovers. This nectar diversity strengthens colonies by ensuring food is available even when trefoil is past its peak.
Although Common Blues also appear inland, coastal colonies in Cornwall are often the most vibrant. Here’s why:
Yet inland, unimproved pastures, old quarries, dune systems, and even wildflower-rich road verges can hold good populations. These pockets, though smaller and often more fragmented, remain important reservoirs for the species, especially where trefoil grows in abundance.
The relationship between the Common Blue and Bird’s-foot Trefoil is delicately timed. A warm spring can bring both species to life early, extending the season. But climate change is adding unpredictability.
If trefoil flowers too early, or if drought forces it to wither before a brood’s caterpillars have matured, colonies can suffer. Similarly, a wet, stormy spring might delay flowering or reduce nectar availability. In a changing climate, maintaining diverse, connected grasslands will be vital to buffer these shifts.
Cornwall’s conservation work is quietly helping to safeguard this relationship. Across the county:
Even small steps, like planting trefoil in gardens or managing local greens for wildflowers, can create stepping stones for the butterfly across Cornwall’s fragmented landscapes.
To see the Common Blue at its best in Cornwall, head for a sunny coastal path in late May or early June. Look for sheltered dips in the grass where trefoil blooms thickly, and you may find males basking with wings wide open, or females weaving low between flowers, searching for just the right place to lay their eggs.
It is a quiet yet intricate scene — one that has played out on these cliffs for countless springs, linking the sky’s blue to the gold of the turf, and tying the life of a butterfly to the flowering of a humble wildflower.
The Common Blue (Polyommatus icarus) is one of Cornwall’s most widespread and eye-catching butterflies, but to see it at its best, you need to know the right season, the right places, and a few observation tips.
Prime Coastal Spots
Inland Highlights
The sight of a Common Blue gliding over a carpet of late spring or summer wildflowers is one of Cornwall’s simplest seasonal joys. Once you learn to link the flash of blue wings to the gold of Bird’s-foot Trefoil, you’ll start spotting them everywhere — from rugged cliff paths to quiet village verges.
