Painted lady (Vanessa cardui)

Vanessa cardui is a well-known colorful butterfly, known as the painted lady, or in North America as the cosmopolitan.

Description
Male and female. Upperside. Ground-colour reddish-ochreous, basal areas olivescent-ochreous-brown; cilia black, alternated with white, Forewing with an outwardly-oblique black irregular-shaped broken band crossing from middle of the cell to the disc above the submedian vein; the apical area from end of cell and the exterior border also black; before the apex is a short white outwardly-oblique streak and a curved row of four round spots, the second and third being small; a marginal pale lunular line with its upper portion most defined and whitish. Hind-wing with a blackish patch from the costal vein across end of cell, a partly confluent recurved discal band, a submarginal row of lunules, and then a marginal row of somewhat scutiform spots; between the discal band and submarginal lunules is a row of five round black spots, which in some examples show a pale and dark outer ring. Underside. Forewing brighter reddish-ochreous, the apical area and outer margin much paler, the apex being olivescent ochreous-brown; discal irregular band as above, subapical white streak, row of spots and marginal lunules distinct; base of wing and interspace before end of cell white. Hindwing transversely-marbled with olivescent ochreous-brown and speckled with black scales; crossed by basal and discal sinuous whitish or pale fascia and intersected by white veins; an outer-discal row of five ocelli, the upper one smallest and usually imperfect, the second and fifth the largest, the fourth with black centre speckled with blue and ringed with yellow, and the second and fifth also with an outer black ring; submarginal lunules purpurescent-grey, bordered by a whitish fascia; outer margin ochreous. Body olivescent ochreous-brown, abdomen with ochreous bands; palpi blackish above, white beneath; body beneath and legs greyish-white; antennae black above, tip and beneath reddish.

Migration
V. cardui occurs in any temperate zone, including mountains in the tropics. The species is resident only in warmer areas, but migrates in spring, and sometimes again in autumn. It migrates from North Africa and the Mediterranean to Britain in May and June, but for decades, naturalists have debated whether the offspring of these immigrants ever make a southwards return migration. Research suggests that British painted ladies do undertake an autumn migration, making a 9,000-mile (14,000 km) round trip from tropical Africa to the Arctic Circle in a series of steps by up to six successive generations.The Radar Entomology Unit at Rothamsted Research provided evidence that autumn migrations take place at high altitude, which explains why these migrations are seldom witnessed.

V. cardui is known for its distinct migratory behavior. In California, they are usually seen flying from north to northwest. These migrations appear to be partially initiated by heavy winter rains in the desert where rainfall controls the growth of larval food plants. Painted lady migration patterns are highly erratic and they do not migrate every year. Some evidence suggests that global climatic events, such as el Niño, may affect the migratory behavior of the painted lady butterflies, causing large-scale migrations.

Based on experimental data, the painted lady's migration pattern in northern Europe apparently does not follow a strict northwest heading. The range of headings suggests that migrating butterflies may adjust their migration patterns in response to local topographical features and weather, such as strong wind patterns. Laboratory-raised autumn-generation painted lady butterflies were able to distinguish a southern orientation for a return migration path. According to the same laboratory-based study, when butterflies were isolated from the sun, they were unable to orient themselves in a specific direction, opposed to those that did have access to the sun. This suggests that V. cardui requires a direct view of the sky, implying the use of a solar compass to orient its migratory direction and maintain a straight flight path.

Mating behavior in relation to migration
V. cardui displays a unique system of continuous mating, throughout all seasons, including the winter. This may be attributed to its migratory patterns, thus significantly affecting its mating behavior. During European migrations, the butterflies immediately begin to mate and lay eggs upon arrival in the Mediterranean in the spring, starting in late May. In the United States, painted lady butterflies migrating towards the north experience poor mating conditions, and many butterflies have limited breeding capabilities. The "local adult generation" develops during this time, roughly from the middle of May through early June in conjunction with the butterfly progression throughout their flight.

During its migratory process, these painted lady butterflies start breeding, and reproduce entirely throughout their migration. Scientists have not been able to find evidence of their overwintering; this may be because they migrate to warmer locations to survive and reproduce. Female painted lady butterflies may suspend their flight temporarily when they are "ready to oviposit"; this allows them the opportunity to continually reproduce throughout their migrations. Because these butterflies are constantly migrating, male butterflies are thought to lack consistent territory. Instead of requiring territory to mate with females and developing evolutionary behavior to defend this territory, the mating butterflies appear to establish a particular "time and place" in certain locations that they find to be suitable for reproduction. More specifically, they locate certain perches, hilltops, forest-meadow edges, or other landmarks where they will stay until, presumably, a female to mate.

Equally important for the reproduction of the painted lady butterflies is the males' exhibition of polygynous mating behavior, in which they often mate with more than one female. This is important for painted lady butterflies because the benefits may supersede the costs of polygynysince no permanent breeding ground is used. Upon mating, which typically occurs in the afternoon, female painted lady butterflies lay eggs one by one in their desired breeding locations. The variety of eclosion locations ultimately dictates the male painted lady behavior.

Female painted lady butterflies have been observed to have a relatively "high biotic potential", meaning they each produce large numbers of offspring. This perpetual influx of reproduction may be a reason why these painted lady butterflies have propagated so successfully. One interesting aspect that scientists have observed is that these butterflies like to fly towards rain. Further studies have suggested that the large amounts of rainfall may somehow "activate more eggs or induce better larval development". Inhabited locations begin to observe a large influx of new generations of painted lady butterflies in the fall, particularly in September and October. Their reproductive success declines relatively throughout the winter, primarily through November. However, they still continue to reproduce—an aspect of butterfly behavior that is quite unique. Scientists hypothesize that these extensive migratory patterns help the painted lady butterflies find suitable conditions for breeding, thus offering a possible reason as to why these butterflies mate continuously.
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https://en.wikipedia.org/wiki/Vanessa_cardui