The Common Blue butterfly, Polyommatus icarus, is a familiar and widespread insect across many regions. Known for its distinctive appearance, this butterfly is often encountered in various open habitats.
Identifying the Common Blue
The Common Blue butterfly displays notable differences between males and females, particularly in their wing coloration. Males exhibit a vibrant, iridescent lilac-blue or bright violet-blue on the upper side of their wings, bordered by a thin black line and a white fringe. Their wingspan ranges from 28 to 36 millimeters.
Females present a more varied appearance. Their upper wings are predominantly brown or black-brown, often with a dusting of blue scales near the body and a row of reddish-yellow or orange spots along the wing edges. The extent of blue on female wings can vary significantly depending on their geographical location. Both sexes share a similar underside pattern, which is greyish or brownish, adorned with numerous small black spots circled in white, and a series of orange spots along the margins of the hindwings.
Where They Live
The Common Blue butterfly thrives in a variety of open, sunny environments. Preferred habitats include grasslands, meadows, roadside verges, and gardens. They are also found in coastal areas, such as sand dunes and undercliffs.
These habitats are suitable due to the abundant presence of their larval food plants and diverse nectar sources for adult butterflies. The species is widespread throughout the Palearctic region, encompassing Europe, North Africa, and temperate Asia. The Common Blue has also established populations in North America.
The Journey from Egg to Adult
The Common Blue butterfly undergoes complete metamorphosis, transitioning through four stages: egg, larva (caterpillar), pupa (chrysalis), and adult. Females lay their eggs individually, often on the buds, flowers, or undersides of leaves of host plants. These eggs hatch into larvae within one week.
The emerging caterpillar is pale green and has a slug-like appearance. Larvae feed on the underside of leaves. They undergo several molts as they grow.
Caterpillars form a mutualistic relationship with ants, secreting a sugary substance that attracts ants, which in turn provide protection from predators. After a period of growth, the caterpillar enters the pupal stage.
The pupa, or chrysalis, is olive green or brown and is formed on the ground or at the base of the food plant. This stage lasts for two to three weeks. The adult butterfly emerges from the chrysalis, dries its wings, and begins its adult life, ready to mate and continue the cycle. The Common Blue often has two or three generations per year in southern regions, while northern populations may have a single brood.
What They Eat and Why They Matter
The diet of the Common Blue butterfly changes throughout its life cycle. In their larval stage, caterpillars feed on plants belonging to the pea family, with Common Bird’s-foot Trefoil being a main food source. Other plants consumed by the larvae include various clovers, medicks, and common restharrow.
Adult Common Blue butterflies feed on nectar from a wide array of flowering plants. They visit various wildflowers such as thistles, knapweeds, and daisies. The adult butterfly uses its long proboscis to access the nectar, which provides the energy needed for flight and reproduction.
The Common Blue butterfly plays a role in its ecosystem as a pollinator. As adult butterflies move from flower to flower to feed on nectar, they transfer pollen, contributing to the reproduction of many plant species. Both the larvae and adult butterflies are part of the food web, serving as a food source for various predators like birds, spiders, and other insects.