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Chalkhill Blue
Insects diurnal

Chalkhill Blue

Polyommatus coridon

A shimmering jewel of the summer downs, the Chalkhill Blue is a master of the limestone slopes. Its delicate silvery wings and fascinating bond with ants make it one of the most enchanting sights of the high summer.

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Quick Identification

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Size

Wingspan of 30–38 mm (1.2–1.5 inches)

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Colors

Males are a pale, shimmering silver-blue with black borders; females are chocolate brown with orange spots (lunules) on the wing edges. Both sexes feature white and black chequered fringes.

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Key Features

  • Pale silvery-blue upper wings (males)
  • Chocolate brown wings with orange spots on edges (females)
  • Distinctive black-and-white chequered wing fringes
  • Spotted underwing pattern with a pale grey or brown base

When You’ll See Them

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Activity pattern diurnal
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Peak hours 10 AM - 4 PM
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Season July-August
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Diet Adults feed on nectar from flowers such as Wild Marjoram, Knapweed, and Scabious. Larvae are specialist feeders, eating only Horseshoe Vetch.
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Habitat Strictly limited to calcareous (chalk or limestone) grasslands with short, sun-warmed turf.

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Behavior

The Chalkhill Blue is a social and highly localized butterfly, often found in large colonies where hundreds of individuals may gather on a single hillside. Males are restless patrollers, spend much of their day flying low over the turf in search of newly emerged females. They have a distinctive, low-level fluttering flight that rarely takes them more than a few feet above the ground.

One of the most fascinating aspects of their behavior is the symbiotic relationship between their larvae and ants. The caterpillars produce honey-dew, a sugary secretion that ants find irresistible. In exchange for this food, ants protect the caterpillars from predators and even carry them into their nests for safety during the pupation stage. As adults, these butterflies are highly sun-dependent; if a cloud passes over, they will instantly land and close their wings, becoming nearly invisible against the dry grass.

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Camera Tips

Capturing the Chalkhill Blue requires a different approach than filming mammals. Because they are small and move rapidly, you should position your camera on a mini-tripod or ground mount just 6 to 12 inches above the soil. Focus your lens on a 'staging area,' such as a cluster of nectar-rich flowers like Wild Marjoram or Scabious, which act as natural magnets for these butterflies during the heat of the day.

Lighting is the most critical factor for a successful shot. Chalkhill Blues are most active in full sun, but direct midday light can wash out the delicate silvery-blue of the male's wings. Position your camera so the sun is at a slight angle to the subject to highlight the texture of the wings and the intricate 'chequered' fringe. If your camera allows, use a high shutter speed or a 'Burst' mode to freeze the motion of their fluttering wings.

Since these butterflies are highly localized, placement is key. Look for south-facing slopes or sheltered 'bowls' in the landscape where heat collects. If you are using a trail camera, look for models with a macro lens or a short minimum focal distance (under 2 feet). Setting the camera to time-lapse mode during the peak hours of 11 AM to 2 PM can also yield excellent results, as it captures the constant movement of the colony without needing to trigger a motion sensor that might be too slow for an insect.

Avoid baiting with artificial sugar water, which can attract wasps or ants that might deter the butterflies. Instead, the 'natural lure' of a well-maintained patch of Horseshoe Vetch or native wildflowers is the most effective way to bring them into your camera's field of view. Check your camera regularly during their short six-week flight season in mid-summer, as this is your only window to see them until the following year.

Similar Species

Species that look similar or are commonly confused with Chalkhill Blue.

Common Blue

The Common Blue is smaller, and the male is a much darker, vibrant violet-blue compared to the Chalkhill's pale silver.

Adonis Blue

The Adonis Blue male has a brilliant, electric sky-blue color and also features chequered fringes, but lacks the pale silvery hue.

Holly Blue

The Holly Blue is found in gardens and woods, lacks chequered wing fringes, and has very few spots on its pale blue underwings.

Frequently Asked Questions

Chalkhill Blue butterflies are most active during the warmest part of the day, typically between 10 AM and 4 PM, provided the sun is shining.
Attracting them is difficult unless you live near a chalk downland. You must provide their larval food plant, Horseshoe Vetch, and maintain a very short, sunny lawn on limestone-rich soil.
Adults drink nectar from various wildflowers like Scabious and Bird's-foot Trefoil, while the caterpillars feed exclusively on the leaves of Horseshoe Vetch.
No, they are highly specialized 'habitat specialists' and are almost never found in suburban gardens unless they are immediately adjacent to protected chalk grasslands.
Look for the pale, almost silvery-blue color of the males (unlike the vibrant violet of the Common Blue) and the distinct black-and-white chequering on the wing edges of both sexes.

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