Common brimstone

Appearance

The adult common brimstone has sexual dimorphism in its wing coloration: males have yellow wings and iridescence while females have greenish-white wings and are not iridescent. This iridescence is affected by environmental factors.

Distribution

The common brimstone can be commonly found throughout the Palearctic. Individuals have been seen from western Europe to east Asia. The high mobility of this butterfly allows it to search widely for new host plant locations and expand its range. While the geographic distribution of the adult is larger than that of its host plant, its range is nevertheless limited by the presence of host plants due to the needs of its larval stage.

Status

As of 2010, ''G. rhamni'' does not appear to have a threatened conservation status according to IUCN standards. However, the butterfly has experienced significant population and distribution reduction in areas such as the Netherlands, where its numbers have declined to the point that based on IUCN criterion, it has reached endangered species status.

Behavior

The common brimstone is one of the longest-living butterflies, with a life expectancy ranging from 10 months to a year. Due to its hibernation and life cycle, it has one generation per year.

Development from the laid egg to the emergence of the imago is approximately 50 days. However, the adult brimstone spends a large portion of its life in an overwintering state.

The brimstone is highly mobile, feeding and travelling to regions ideal for hibernation during the late summer and fall, and returning to regions ideal for mating and egg-laying during the spring.

Both the larval and adult common brimstone exhibit cryptic colouration, meaning they match the colour of their habitats. Larvae are so difficult to see due to this colouration that they can remain in the open undetected.

When not eating, the caterpillars remain still in a position alongside the midrib of leaves, making them even more difficult to spot.

Adult brimstones are leaf-mimics, as they share similarities in shape, colour, and pattern to leaves. This allows them to blend in with their surroundings during vulnerable times like diapause. When picked up, the butterflies become rigid and hide their legs from view in order to decrease their chances of being recognised.

Habitat

The common brimstone uses various environments for different stages of its life cycle. The butterfly inhabits wetlands during mating and breeding season, as they provide ideal areas for oviposition due to an abundance of host plants like the alder buckthorn.

The common brimstone prefers laying eggs on younger host plants with late bud-bursts that are isolated from other plants in the area and exposed to both open space and sun.

During the winter, adult brimstones travel to woodlands to hibernate, as they provide ideal overwintering sites with shelters such as evergreen foliage and holly. The common brimstone has an appearance that is highly similar to the leaves of these plants, so during hibernation it can remain hidden. In other seasons, habitat selection is also affected by the abundance of nectar as a food source for adult brimstones.

Predators

Like most woodland Lepidoptera, ''G. rhamni'' is preyed upon by many species of birds and wasps. Both larvae and adult brimstones fall victim to predation and use means such as protective coloration and mimicry to avoid this fate.