UK Butterflies
Building a Community of Responsible Butterfly Enthusiasts in Britain & Ireland
Building a Community of Responsible Butterfly Enthusiasts in Britain & Ireland
Wingspan
♂ 63 - 68 mm, ♀ 67 - 75 mm
Checklist Number
59.026
The Peacock is a familiar sight in gardens across the British Isles and is unmistakable, with quite spectacular eyes on the upperside of the hindwings that give this butterfly its name. These eyes must appear very threatening to predators, such as mice, that confront this butterfly head-on, where the body forming a "beak", as shown in the image below.
The underside is a different matter altogether, being almost black, providing perfect camouflage when the butterfly is at rest on a tree trunk, or when hibernating. In addition to camouflage and large eyes, the butterfly is able to make a hissing sound by rubbing its wings together that is audible to human ears. All in all, this butterfly must appear very threatening to any predator that might come across it. This is a highly mobile butterfly that occurs throughout the British Isles, including Orkney and Shetland, although it is not found in parts of northern Scotland. However, its range does seem to be increasing, with sightings from new areas being recorded every year.
| Family: | Nymphalidae | Rafinesque, 1815 |
| Subfamily: | Nymphalinae | Rafinesque, 1815 |
| Tribe: | Nymphalini | Rafinesque, 1815 |
| Genus: | Aglais | Dalman, 1816 |
| Subgenus: | ||
| Species: | io | (Linnaeus, 1758) |
Description to be completed.
The distribution data (2000-2009) has been made available through the generosity of Butterfly Conservation and any subspecies distribution is taken from Riley (2007). Click here to see the distribution of this species together with site information overlaid.
This butterfly can turn up almost anywhere, given its broad distribution. This butterfly is often encountered while hibernating in outbuildings, such as a garage, shed or barn, where they are often in the company of other individuals. Other hibernation sites include hollow trees and wood piles, where their dark undersides provide excellent camouflage.
Although small decreases in population have been observed, this species seems to be faring well and this common and widespread species has shown signs of colonising the few remaining areas in northern Scotland where it has not historically been found. This butterfly is not, therefore, a species of conservation concern.
The table below shows the occurrence (distribution) and abundance (population) trends, using information from The State of the UK's Butterflies 2015 (Fox, 2015). Any UK BAP status is taken from the UK Biodiversity Action Plan (UK BAP) (2007 review).
1976-2014 (%) | 1976-2014 (%) | 2005-2014 (%) | 2005-2014 (%) |  +16 | +17 |  +3 | +21 |
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This butterfly is generally single-brooded. However, in good years, a small second brood may appear. Adults may be seen at any time of the year, with warm weather waking them from hibernation. The majority emerge from hibernation at the end of March and beginning of April. These mate and ultimately give rise to the next generation that emerges at the end of July.
The adults spend most of the morning nectaring. Males set up territories around midday, often on the sunny side of a wood, where they wait for a passing female. Males will fly up at any dark object, which is one way of sexing this species since the two sexes are very difficult to tell apart, being almost identical in appearance. When a female is found she flies off, trying to escape the male that is in pursuit. If he succeeds in staying with her then the pair mate. Females subsequently take great care when egg-laying, selecting foodplants that are in full sun.
Adults emerging in summer nectar on a variety of flowers, building up essential body fats before overwintering.
Adults feed primarily on Betony (Betonica officinalis), Blackthorn (Prunus spinosa), Bluebell (Hyacinthoides non-scripta), brambles (Rubus spp.), Buddleja (Buddleja spp.), Bugle (Ajuga reptans), Common Fleabane (Pulicaria dysenterica), Cuckooflower (Cardamine pratensis), dandelions (Taraxacum spp.), Devil's-bit Scabious (Succisa pratensis), Ground-ivy (Glechoma hederacea), hawkweeds (Hieracium spp.), Hemp-agrimony (Eupatorium cannabinum), ragworts (Jacobaea spp.), Sap (N/A), thistles (Carduus spp. and Cirsium spp.), Water Mint (Mentha aquatica), Wild Marjoram (Origanum vulgare), Wild Privet (Ligustrum vulgare), Wild Teasel (Dipsacus fullonum) and Yarrow (Achillea millefolium).
Females lay one or more egg clusters of up to 400 eggs on the underside of a Nettle leaf. These are laid in untidy piles, rather than being laid neatly side-by-side. The nettle patches chosen are usually in a more-sheltered position than those selected by the Small Tortoiseshell. Eggs hatch in 1 to 3 weeks.
"On May 12th, 1908, at Breinton, Hereford, the author captured four hibernated females of this species, which were placed on growing plants of stinging nettles (Urtica dioica). At noon on the 16th all four butterflies were observed at rest with closed wings on the under side of the leaves, busy depositing; they all hung motionless (excepting the movements of the abdomen) for a long time. One finished depositing at 2.30 p.m. As several eggs were already laid by 12.30, when they were first noticed, the time occupied by egg laying extended over two hours. It is curious that all four specimens chose exactly the same hour to start laying their eggs, as the weather was similar to that of the previous days. The eggs are laid in a dense mass, piled up one above the other, being six or more deep in the middle; it is difficult to estimate the number so laid, probably between 450 and 500 or more, as from 180 to 200 can be counted on the outer surface of the mass of eggs. Each of the four butterflies laid about the same quantity, each depositing them in a single heap on the under side of the leaves. The egg, in proportion to the butterfly, is very small, being only 0.80 mm. high, of an oblong form. Upon examining a large number of eggs it was found that all had eight longitudinal keels (therefore in V. io this number is constant), starting near the base and running up the side over the crown, where they are elevated and prominent; they disappear at the edge of the micropyle. They resemble fluted frosted glass. The spaces between the keels are concave and transversely ribbed. The micropyle is finely pitted, the base rounded and smooth. The colour when first laid is a clear yellowish-green, which is retained until about the tenth day, when very slight darker green blotches appear round the egg; on the twelfth day the blotches are slightly increased in depth. On the thirteenth day the dark head of the larva appears and finally becomes clearly visible, and the rest of the egg an opaque green; the dark heads giving the entire batch a deep leaden hue. They all hatched on the fourteenth day, viz., May 30th, 1908." - Frohawk (1924)
The behaviour of the larva is very similar to that of the Small Tortoiseshell, the two species often being seen together. In the first instar, Peacock larvae are very similar to those of the Small Tortoiseshell. However, mature Peacock larvae are jet black for the most part, whereas Small Tortoiseshell larvae are typically dark green with a pair of yellow stripes running down the length of their sides.
On emerging from their eggs, Peacock larvae build a communal web near the top of the plant and from which they emerge to bask and feed and are usually highly conspicuous. As the larvae grow, they move to new plants, building new webs along the way. Webs are decorated with shed larval skins and droppings and are easily found.
Larvae have several techniques to avoid predation. When disturbed, a group of larvae will often jerk their bodies from side to side in unison, which must be a formidable sight to any predator. The larvae will also regurgitate green fluid and will, if necessary, curl up in a ball and drop to the ground. Larvae feed both during the day and at night. There are 5 instars in total.
The primary larval foodplant is Common Nettle (Urtica dioica). Hop (Humulus lupulus) and Small Nettle (Urtica urens) are also used.
"The larva eats away the crown of the egg, and all hatch at once. Those at the bottom of the batch immediately start feeding through the leaf, and all live in a dense mass, spinning a web over the leaf. Directly after emergence the larva measures only 1.6 mm. long; the body is cylindrical; the head large, black and shining, beset with fine black hairs. On the body are four longitudinal rows of long, fine, black, simple hairs with bulbous bases; they are slightly curved and have the extreme tips very slightly clubbed and whitish. On the ventral surface and claspers are paler fine straight hairs; the spiracles are outlined with black. The surface is finely granular, with minute, raised, dark points. The colour is a very light ochreous-green, almost white-green." - Frohawk (1924)
"The first moult was on June 5th, 1908, the first stage lasting six days. Before the second moult, nine days old, it measures 8 mm. in length. It is a good deal similar to the previous stage; the base of the longest hairs now form black conical tubercles, which are beset with bristles, and each terminates in a long, slightly serrated black hair. There are numerous black serrated hairs of different lengths, some extremely small, scattered over the body, which is granulated with fine black points. The head is shining black, with minute black bristles. The surface of the body is very shining, of a mottled olive-brown, blotched with pale ochreous round each of the largest tubercles. They live and feed in company. Preparatory to moulting they all assemble in a dense mass on a thick carpet of web spun over the eaten part of the plant, and thereon, packed together, undergo the second moult. When disturbed they all throw up the anterior half of their bodies in the form of a hook (thus c__) and remain so for a few minutes." - Frohawk (1924)
"The second moult occurred on June 9th, 1908, the second stage occupying four days. Before the third moult, thirteen days old, it measures from 12.7 mm. to 14.8 mm. long. In this stage a further development in the size of the tubercles is noticeable, especially the two dorsal rows, which are of considerable length and terminate, as all the shorter ones do, with long, slightly curved hairs. The ground colour is purplish-dark-brown, the longer hairs, which are scattered over the body, are placed on white dots. The head and other details of the surface are as in the previous stage; the claspers are pale olive-ochreous. They still live gregariously, and, as in the previous stage, prior to moulting they all assemble in a dense pack, forming a conspicuous black mass. In this stage they consume a great quantity of food; and when touched or irritated exude from the mouth a comparatively large drop of green liquid; and when slightly disturbed they throw up their heads and fore part of the body as in the last stage, and if still further annoyed or shaken they fall to the ground with much wriggling, at the same time lowering themselves by a silk thread." - Frohawk (1924)
"The third moult June 13th, 1908. The third stage also lasted four days. Before fourth moult, eighteen days old, the larva is 25.4 mm. in length; very similar to the previous stage. All the tubercles are well developed, the two dorsal rows being about twice the length of the sub-dorsal and lateral series. The white spots are now more distinct and numerous. The head and legs are shining black, as well as the anal pair of claspers. The ground colour is a purple-black; in other respects the details are the same as in the previous stage. Before moulting they again assemble in a dense mass." - Frohawk (1924)
"The fourth and last moult took place on June 18th, 1908, the fourth stage lasting five days. After fourth moult, fully grown, about twenty-eight days old, it averages in length about 41 .3 mm., some specimens as much as 44 mm. long. It is fairly cylindrical and comparatively slender; the first segment is much the smallest. There are six longitudinal rows of black shining spines from the fifth to eleventh segments inclusive; the second and third segments have each only two dorsal spines, which are longer than those on the other segments; the fourth and anal segments have each four spines; the first segment has no spines, but a transverse ridge of fine black hairs. The spines are sub-dorsal, super-spiracular and sub-spiracular. They are long and shining black, sharply pointed, and bear numerous bristles of various lengths; the body is densely covered with minute black bristles, which adds intensity to the rich velvety-black ground colour. At the segmental divisions the surface is smooth and of a dull leaden-black. Each segment is encircled with numerous pure white globular warts, each emitting a fine white hair; the largest are in front of the spiracles. On the first segment is a dorsal, shining, black, transverse disc, and two round ones on the anal segment; the first is small and adjoins the eleventh segment, the other forms a large rounded knob on the extremity. The head and legs are shining black and thickly studded with black bristles of varying lengths; the claspers are ochreous-brown at the base, the middle portion bright ochreous, the foot palest. Several of the larvae were fully grown on June 24th (the fifth stage occupying six days), making the larval period twenty-seven days: twenty-five days feeding and two days occupied in changing to pupa." - Frohawk (1924)
The larvae disperse as they become fully grown, and eventually wander off to find a suitable pupation site. The pupa is formed head down, attached to a stem or leaf by the cremaster. The pupa has 2 colour forms - yellow and dark grey - the resulting colour depending on the site chosen for pupation. This stage lasts between 2 and 4 weeks, depending on temperature.
"The pupa averages in length 25.4 mm. male, and 28.6 mm. female. Dorsal view: The head with two frontal, diverging, sharply pointed horns; the base of the wing bi-angular; it is contracted across the waist, and swollen at the third abdominal segment, and tapering to the anal segment, which terminates in a long cremastral point. Side view: Head sharply pointed; the meso-thorax rising to a prominent angular point, sunken at the meta-thorax and first abdominal segment; the abdomen forming a gentle curve to the long, flattened cremastral process, which is truncated at the extremity and amply provided with hooks; ventral surface bulging at the apex of the wings, then forming a slight convex curve to the head. Colour: Directly after pupation the thorax is bright green, the wings and abdomen yellow-green. In a short time the mature colouring is formed. The pupae vary from light green-yellow to pinkish-grey; others are olive speckled with blackish. The normal colouring appears to be the yellow-green form, which is the most constant type; this has the ground colour a light yellow-green, greenest on the wings and yellowest on the dorsal area of the abdomen, and washed with gold, chiefly on the head, thorax and inner edge of the wings. On the third, fourth; fifth, sixth and seventh segments are a pair of sub-dorsal, sharply pointed spikes, rose-red at the base and with shining black tips; on the second abdominal segment these are represented by a mere black point gilded round the base; they are absent on the first segment, but duplicated on the meta- and meso-thorax by black dots on a gilded ground. There are no medio-dorsal abdominal points; the spiracles are black; there are numerous black dots, very small, scattered over the abdomen. The head horns have black lines on the upper and inner edges; the wings are speckled with black on a pink dash along inner edge, faintly duplicated obliquely across the centre, and a faint blotch at the apex; the cremastral process with a black line along the lateral edge. The entire surface is finely granulated. The darker pupae are more or less reticulated, speckled and blotched with black, and only very slightly metallic. Before emerging the pupa darkens, finally becoming dusky brown, the wing markings showing indistinctly. It is firmly attached by the cremastral hooks to a pad of silk. The pupal period lasts from twelve to fourteen days. The first imagines emerged on July 7th, 1908. Although this species sometimes pupates on the nettles upon which the larvae have been feeding, as a rule the caterpillars leave the plants and roam a considerable distance to find a suitable place for pupation, which apparently is some branch or leaf stalk of a bush or tree. The author knows of an instance of an entire brood of io larvae which ascended a large oak tree, growing by the edge of a wood, for the purpose of pupation. When first detected the larvae were about fifteen feet from the ground and were marching in a body up the main trunk, and shortly afterwards they dispersed and spread about the branches. The nettles upon which they had lived grew about ten feet away from the tree." - Frohawk (1924)
The following links provide additional information on this butterfly.
