Imago

 

emergence | feeding | mate location | courtship | reproduction | mate location

perching, patrolling and territories | the daily routine | adult lifespan | anatomy

 

 

Gonepteryx rhamni, female drying wings after emergence

Emergence

Emergence of the fully developed adult butterfly from the pupa is triggered by factors including humidity, temperature, light level, and time of day. Most butterflies emerge shortly after dawn.

Prior to emergence the spiracles ( breathing holes ) of the butterfly within are linked by short tubes to the spiracle openings on the pupa shell. Air is drawn in through these tubes, enabling the butterfly to pump up it's body, which causes the shell of the pupa to split, just behind the head.

The butterfly then forces it's way out, and uses it's legs to pull itself clear of the empty pupa. If the pupa was attached to a twig or leaf, the butterfly usually suspends itself from the pupa shell while it expands it's wings.

Skippers and many moths pupate within some sort of silken nest or cocoon. Prior to emergence they usually eject solvents from the proboscis which dissolve away the silk and enable them to emerge. Other butterflies ( e.g. certain Satyrines and Lycaenids ) pupate in subterranean cells. In these cases they have to crawl about until they can find a twig or firm stem from which they can suspend themselves.

Having settled into position, the butterfly then spends several minutes hanging virtually motionless. During this time it pumps fluids into the wing veins, causing the wings to expand to their full size.

After allowing time for the wings to harden, male butterflies usually fly off to seek nectar or other forms of sustenance. Females of many species however tend to stay within a few metres of the emergence site until mated.

In most species males emerge at least a day or two before females. The reason usually given for this is that females usually mate on the day they emerge, so it is advantageous if there are already plenty of males available to them.

An equally likely explanation that is not mentioned in literature is that males are not usually capable of mating until they are 2 or 3 days old, as they often need to feed in order to accumulate alkaloids that are vital to reproduction. Well known examples of this include the Purple Emperor whose males feed at dung, Swordtails and Daggerwings which feed at urine, Longwings which feed on pollen, and Glasswings such as Pteronymia sao which feed on decomposing plant material. The latter derive pyrrolizidine alkaloids from the plants, which are used in the production of pheromones and defensive toxins, as well as for reproductive purposes.

Feeding behaviour

Males of many tropical species are regularly observed imbibing dissolved minerals from damp mud, bird droppings, aphid secretions, sap runs, or even from carrion. The minerals are later passed to the females during copulation, and may contain vital nutrients necessary for the production of fertile eggs.

In temperate regions both sexes of most species feed primarily at nectar, but males of several species, e.g. Apatura iris, Lysandra coridon, Pyrgus alveus, Thymelicus lineola and Mellicta athalia commonly imbibe mineralised moisture, or visit dung.

Anteos menippe ( Peru ), male imbibing dissolved minerals from damp sand.

 

 

Mate location

Butterflies generally have short lives, females often having less than a week to find a mate, copulate, search for oviposition sites, and lay their eggs. Rapid mate location and recognition is vital, and butterflies cannot afford to waste time on too many fruitless encounters with species other than their own.

Butterflies can see all the colours of the visible spectrum, plus ultra violet. Males of brightly coloured species such as the orange Julia Dryas iulia, and yellow Phoebis and Eurema species are able to detect others of their own kind from several meters away, and use this ability to home in on feeding grounds.

Experiments with bright blue Morpho species show that waving a piece of blue paper in the air is very effective at attracting them towards observers. These facts prove that butterflies use colour to locate others of the same species, and it seems logical to assume that colour plays a significant role in mate location.

Pattern recognition is a different matter, and only comes into play when the butterflies are in close proximity. Very conspicuous patterns such as the black and yellow pattern of Papilio machaon, or the black, red and white of Vanessa atalanta may be recognised at close distances, but it is obvious that subtle patterns cannot be.

To illustrate this point, simply imagine an alpine meadow with a mixed population of Erebia species - all are plain drab brown insects of similar size and shape, differing only in minute details that could not possible be seen with the poor resolution of a butterfly's eyes.

The same argument applies to the Pyrgus skippers, the Melitaea Fritillaries and the numerous Polyommatine blues, where many very similarly patterned and closely related species share the same habitat. Colour and pattern can therefore play only a fairly minor role in mate recognition.

In some species courtship is very brief, in others it is protracted and involves complex rituals. Male and female Wood Whites Leptidea sinapis for example are often seen sitting facing each other, exchanging chemical messages with their antennae. The male repeatedly flicks out his long proboscis, whipping the female alternately on the underside of her left and right wings. Both sexes periodically flick open their wings, and it is clear that the butterflies are communicating something. The ritual does not appear to instigate copulation, so the nature of the "messages" is unclear.

The courtship behaviour of butterflies in general are poorly studied, but it is clear that in most species the females will not permit males to copulate until they have completed an often complex ritual. This typically begins with the males releasing pheromones, which leads to the female settling on foliage. The male might then begin a "courtship dance" around the female, or use some other form of physical stimulus to which the female reacts in a particular way. Each stimulus must elicit the "correct" response, producing a chain reaction of events that culminates in copulation.

Small Tortoiseshells Aglais urticae have a protracted courtship which can last for several hours. The male follows the female as she flies from place to place, and when she settles and opens her wings, he walks onto her hindwings, tapping them with his antennae. This process is repeated many times over several hours, during which the male will drive off any other intruding males. Eventually the female leads him to a sheltered spot, typically underneath a small bush, where copulation takes place.

Brimstone Gonepteryx rhamni males are also often seen "wing-walking" on females, but this is invariably followed by the female inverting her wings and raising her abdomen - a signal to the male that she is rejecting his advances, and a sure sign that she has already mated ( females of most butterflies only mate once ).

When female Brimstones are receptive, copulation takes place almost instantly, without any observable pre-nuptial ritual. Most butterflies remain copulated only for an hour or so, but the Brimstone is quite remarkable in this respect - I once found a pair of Brimstones which remained copulated beneath a bramble leaf for an amazing 17 days before finally parting company !

Lysandra bellargus copulating pair ( female on left )

Males usually mate with several females in the course of their lives. Females of certain long-lived species such as the Monarch Danaus plexippus will mate with several males, but in the majority of species females normally only mate once. After mating, the genital opening on the females of Marsh Fritillaries Euphydryas aurinia and some other species becomes sealed, physically preventing them from mating with other males. Males of the Apollo butterfly Parnassius apollo seal the female genital opening with a structure called a sphragis, preventing other males from copulating with them.

The behaviour of Heliconius erato, as observed by myself in Costa Rica, is fascinating to watch. Female pupae, when close to emergence, often have several male adults in very close attendance. A frantic battle takes place the instant the female hatches, as all the males struggle to copulate with her, not even allowing her time to expand and dry her wings. The mated pair then have to endure the attention of the remaining males, which are often extremely persistent, trying to prise the pair apart. Eventually, with the approach of dusk, the unsuccessful males disperse, allowing the pair to remain copulated until the next morning. The butterflies can live for many months, but spend their entire lives within a restricted area. As a result of this minimal contact with other populations, the species has developed a vast number of localised "races" and colour forms.

The daily routine

Male and female butterflies of any given species usually behave very differently. In most species the males are highly active, and their behaviour follows a predictable cycle of feeding, basking, and patrolling in search of females. Males of other species are often highly territorial, and will defend their territories against other insects including wasps, flies, and flying beetles. If another male of the same species enters their territory, they engage in an aerial sortie, spiralling high above the trees until the intruding butterfly is ousted.

Female butterflies live entirely different lives. Prior to mating they are often sedentary, remaining very close to the spot where they emerged from the pupa. After mating they seek places to lay their eggs, but usually fly only short distances between bouts of egg laying.

These differences in behaviour are reflected in their appearance - males need to be noticed, so are generally more colourful than females. The Adonis Blue Lysandra bellargus from Europe is a good example : males are a brilliant iridescent blue colour, but the females are drab dark brown creatures - they spend most of their time crawling about on the ground amongst short grasses, looking for places to lay their eggs, but need to bask occasionally so they can raise their body temperatures. When basking on the ground, their drab colouration helps them to escape the notice of insectivorous birds.

Adonis Blue Lysandra bellargus - male	Adonis Blue Lysandra bellargus - female

Lifespan

The whole lifecycle from egg to adult can take just 3 weeks to complete in many tropical species. In temperate regions the lifecycle of the summer generation may be complete within about 6 weeks, but many species only produce a single generation in a year. In sub-arctic and alpine zones some species ( e.g. Parnassius eversmanni, Oeneis alpina and Boloria natazhati ) take 2 years to complete their lifecycle.

The lifespan of the adult butterfly varies greatly from species to species. Butterflies kept in captivity, if fed regularly can live for quite long periods. Wild butterflies are subject to predation and the extremes of climate, so while they have the potential in most cases to live for 3 or 4 weeks, in practice the average lifespan is just 7 or 8 days.

There are however several notable exceptions to this general rule. Some butterflies, e.g. Monarchs, Commas and Tortoiseshells, hibernate as adults, and these species often live for several months. The longest lived European species are the Brimstone and Peacock - both emerge in early July, and often survive until the following June.

Certain tropical species are also capable of surviving for equally long periods - in South America for example, Taygetis mermeria and certain Ithomiine and Danaine species are known to sometimes live for up to 11 months. Various Heliconius species, when reared in captivity can live for even longer, but the absence of faded and worn specimens in the wild would seem to indicate that longevity in nature is substantially less.

 

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