Aglais io, the European peacock, or the peacock butterfly, is a colourful butterfly, found in Europe and temperate Asia as far east as Japan. The peacock butterfly is resident in much of its range, often wintering in buildings or trees. It therefore often appears quite early in spring.
The peacock butterfly has figured in research in which the role of eyespots as an anti-predator mechanism has been investigated. The peacock is expanding its range and is not known to be threatened.
The butterfly has a wingspan of 50 to 55 millimetres (2 to 2+1⁄8 in). The base colour of the wings is a rusty red, and at each wingtip it bears a distinctive, black, blue and yellow eyespot. The underside is a cryptically coloured dark brown or black, mimicking a dead leaf.
There are two subspecies: A. io caucasica (Jachontov, 1912), found in Azerbaijan, and A. io geisha (Stichel, 1908), found in Japan and the Russian Far East.
The peacock can be found in woods, fields, meadows, pastures, parks, and gardens, from lowlands up to 2,500 metres (8,200 ft) elevation. It is a relatively common butterfly, seen in many European parks and gardens. The peacock male exhibits territorial behaviour, in many cases territories being selected en route of the females to oviposition sites.
The butterfly hibernates over winter before laying its eggs in early spring, in batches of up to 400 at a time. However, recent studies in Belgium have shown that peacock butterflies reproduce in two periods: early spring and early summer, and a possible third period in autumn. They found that peacock butterflies show flight peaks in early July and early August to early October, with the emergence of butterflies with good-conditioned wings, which shows signs of new offspring. The olive green eggs are ribbed. They are laid on both the upper parts and the undersides of leaves of nettle species and hops.[citation needed] The caterpillars hatch after about a week. They are shiny black with six rows of barbed spikes and a series of white dots on each segment. The chrysalis may be either grey, brown or green, and may have a blackish tinge. The caterpillars grow up to 42 millimetres (1+5⁄8 in) in length.
The primary food plants of European peacock larvae are stinging nettle (Urtica dioica), hop (Humulus lupulus), and the small nettle (Urtica urens).
The adult butterflies drink nectar from a wide variety of flowering plants, including buddleia, willows, dandelions, wild marjoram, danewort, hemp agrimony, and clover; they also use tree sap and rotten fruits.
Aglais io employs a monogamous mating system, which means that they only mate with one partner for a period of time.[citation needed] This is due to their life cycle in which females are receptive only during an eclosion period, after overwintering. The pairs only mate once after overwintering, as it is very difficult to find a receptive female after that period. In species where the range of the females is not defensible by a male, the males must defend a single desirable area that females will come through, such as dense food areas, watering holes, or favourable nesting sites. The males then attempt to mate with the females as they are passing through.
Holding a desirable territory increases the male's likelihood of finding a mate and therefore increases his reproductive success. However, each individual needs to weigh the benefits of mating with the costs of defending a territory. Aglais io exhibits this type of territorial behaviour, and must defend a desirable territory from other males. If only one of the males knows the territory well, he will successfully chase off any intruders. On the other hand, if both males are familiar with the territory, there will be a contest between the two to determine which of them stays in the territory. The most desirable sites are those that will increase the male's quota of females. These sites are generally feeding and oviposition sites, which are sought after by females. This territorial behaviour is reinforced by the fact that these sites are all concentrated. If the valuable resources were dispersed, there would be less observable territorial behaviour.
To find mates and defend their territory, Aglais io exhibits perching behaviour. The male butterflies will perch on an object at a specific height where they can observe passing flying objects. Every time they see a passing object of their own species or of a relevant species, they will fly straight towards the object until they are approximately 10 cm away. If they encounter a male, the resident male will chase him off his territory. If the resident male encounters a female, he will pursue her until she lands and mating will occur. The courtship is extended in this species. The male goes through a long chase before the female allows him to mate. He must demonstrate high performance flight.
The monandrous mating system has caused the evolution of a shorter life span in males of this species. In polygynous butterflies, the male's reproductive success is largely dependent on life span. Therefore, the longer a male lives, the more he can reproduce, so he has a higher fitness. Therefore, males tend to live as long as the females. In A. io the synchronous eclosion at the end of winter cause males to only mate once. Their reproductive success is therefore not linked to how long they live, and there is no selective pressure to live longer. Therefore, the life span of males is shorter than the lifespan of the females.
Like many other butterflies that hibernate, the peacock butterfly exhibits many anti-predator defence mechanisms against would-be predators. The peacock butterfly's most obvious defense comes from the four large eyespots that it has on its wings. It also uses camouflage and can emit a hissing sound.
