The habitats they occupy are determined by where their larval butterfly effect 2 sex grow, and by the availability of adult food sources and roosting sites. Suitable habitats are often highly localised so consequently many species have an extremely patchy distribution. Nevertheless all species whether humans or butterflies are to a greater or lesser extent genetically programmed to ‘leave home’, dispersing to explore new areas. It is important to understand the difference between dispersal and migration.
The term dispersal is used to describe random and aimless movement away from the site where a butterfly emerges. Dispersing butterflies are easily diverted from their course by minor changes in wind direction or obstacles in their path. They will for example fly around the edge of a block of forest rather than fly through it or over it. When they encounter hostile habitats such as arable farmland, lakes, rivers, roads or buildings they steer left or right to try to find a route around them. The term migration refers specifically to medium or long distance directional movements.
Migrating butterflies have a strong purposeful flight and are unaffected by obstacles or hostile landscapes. Their flight path is not affected by wind:- C. Migrations usually involve mass movements – a flight of Vanessa cardui in California in 1924 was estimated to contain about 3000 million butterflies. The diagram above illustrates the differences between dispersal and migrational flight patterns. The blocks of green represent ‘hostile’ habitats, e. Woodlands become overgrown and shade out herbaceous plants on which the caterpillars of many butterflies depend. Heathlands catch fire, grasslands become overgrown with scrub, deserts expand, cliffs crumble away.
Species at the edge of their natural distribution range tend to inhabit sites which are sheltered from bad weather. Pearl-bordered Fritillaries for example occupy open meadows in mainland Europe, but in Britain such habitats are too cold for them so they form colonies in sheltered woodland clearings instead. Many other factors can trigger dispersion e. The larvae scour their habitat, devouring every available leaf of their foodplant. Ultimately they sense imminent starvation, and undergo a chemical change which switches them into a high activity phase causing them to swarm across the surrounding countryside in search of food. In Britain adults of Clossiana euphrosyne nectar almost exclusively on bugle – Ajuga reptans.
They lay their eggs on dead bracken or dry grass stems, but their caterpillars feed on Viola. Many other species however are not so lucky – their larval foodplants may grow in entirely different places from the adult food sources, so they need to commute between breeding and feeding sites. In temperate regions mountainous areas such as the Alps, Pyrenees, Rockies and Tien Shan, land above about 1800m is covered in snow for much of the year. In the Andes, the Himalaya and the mountain ranges of New Guinea areas as low as 3000m are subject to seasonal snow cover. Coppers, Ringlets, Apollos and Heaths nectar avidly at the abundant flowers. Most of these species are sedentary insects, forming highly localised breeding colonies. Other species such as Clouded Yellows, Whites and Swallowtails are nomadic, and migrate down to the lowlands in late summer to breed.