Insects diurnal

Common Blue

Polyommatus icarus

The most widespread of all the 'blue' butterflies, the Common Blue is a flying sapphire that brings life to summer meadows. Whether it's the brilliant azure of the male or the subtle orange-flecked brown of the female, these tiny insects are a backyard treasure.

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Quick Identification

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Size

Wingspan of 29–35 mm (1.1–1.4 inches); body length approximately 15 mm (0.6 inches)

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Colors

Males are bright lilac-blue with thin black borders and white fringes; females are chocolate brown with orange spots along the edges and varying levels of blue dusting.

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Key Features

Vivid blue upper wings in males
Row of orange 'crescent' spots on the wing margins (especially visible in females)
Underside wings are grey-beige with distinct white-ringed black spots
White fringe along the outer wing edges

When You’ll See Them

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Activity pattern diurnal

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Peak hours 10:00 AM - 4:00 PM

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Season May-September

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Diet Adults drink nectar from wildflowers like Bird's-foot Trefoil, clovers, and knapweed. Caterpillars feed on legumes, particularly Bird's-foot Trefoil.

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Habitat Widespread in open grassy areas, including suburban gardens, meadows, roadsides, and coastal dunes.

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Behavior

The Common Blue is a sun-loving butterfly that is most active during the warmest parts of the day. They have a characteristic low, fluttering flight pattern, rarely rising more than a few feet above the vegetation. Males are highly territorial and will frequently perch on tall grass stems or flower heads to scan for mates, aggressively chasing off other males that enter their immediate vicinity.

One of their most fascinating behaviors occurs at dusk; they often roost communally, with several individuals gathering on the same grass head or flower spike to spend the night. They typically rest head-downwards during these periods. The larvae of the Common Blue also share a symbiotic relationship with ants; the caterpillars produce a sweet secretion that ants feed on, and in return, the ants protect the caterpillars from parasitic wasps and other predators.

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Camera Tips

To successfully capture the Common Blue on an AI camera, positioning is your most important variable. These butterflies are low-fliers, so avoid mounting your camera on high fences or trees. Instead, use a ground-level stake or a mini-tripod to place the lens between 12 and 24 inches from the ground. Aim the camera at a cluster of nectar-rich 'landing pads' like Bird's-foot Trefoil or Wild Marjoram, which are irresistible to this species.

Because these insects are small and fast-moving, your camera's shutter speed and trigger sensitivity need to be high. If your AI camera allows for custom zones, focus the detection area tightly on the flower heads. Morning is the best time for high-quality stills; before the day gets too hot, Common Blues will 'bask' with their wings open to absorb solar energy. Position your camera facing East to catch the early light hitting their wings, which creates a stunning iridescent glow that the AI can easily identify.

If you want to record their unique roosting behavior, look for tall, dry grass stems in a sheltered corner of your yard. Setting your camera to capture time-lapse or short video clips in the hour before sunset can reveal them gathering for the night. Since they are attracted to specific host plants, planting a 'larval patch' of legumes will ensure they stay in your camera's field of view throughout their entire life cycle, from egg-laying to the emergence of the next generation.

Similar Species

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

Holly Blue

Flies much higher around shrubs and trees; underside is pale silvery-blue with tiny black dots rather than white-ringed spots.

Chalk Hill Blue

Much larger and paler 'milky' blue; found almost exclusively on chalk downlands where Horseshoe Vetch grows.

Brown Argus

Looks very similar to a female Common Blue but lacks the blue dusting and has a different arrangement of spots on the wing underside.

Frequently Asked Questions

Common Blue butterflies are most active between 10:00 AM and 4:00 PM when the sun is at its strongest. They require the sun's heat to warm their flight muscles, though you can often find them resting on grass stems early in the morning or late in the evening.

The best way to attract Common Blue butterflies is to plant their favorite food sources. For the adults, provide nectar-rich flowers like Knapweed and Clover. Most importantly, leave a patch of 'wild' lawn containing Bird's-foot Trefoil, which is the primary food source for their caterpillars.

Adult Common Blue butterflies feed on the nectar of a variety of wildflowers, with a strong preference for legumes. Their caterpillars (larvae) have a narrower diet, feeding almost exclusively on the leaves of Bird's-foot Trefoil and sometimes other pea-family plants.

Yes, they are very adaptable and are frequently found in suburban gardens, parks, and school grounds, provided there are patches of long grass and wildflowers nearby where they can breed and find shelter.

Common Blues have a 'cell spot' on the underside of their forewings and typically fly low over the grass. Holly Blues lack this spot, have tiny black dots on their pale blue undersides, and are usually seen flying higher up around shrubs and ivy.

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