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The butterfly
lifecycle
1 - Egg
- anatomy, oviposition
2 - Caterpillar
- anatomy
3 - Caterpillar
- hatching, feeding and development
4 - Caterpillar
- cannibals, carnivores and myrmecophiles
5 - Caterpillar
- survival mechanisms,
armature, camouflage / disguise
6
- Caterpillar
-
co-evolution with plants
7 - Chrysalis
- pupation, metamorphosis
8 - Adult
- emergence, feeding
9 - Adult
- mate location and courtship
10 - Adult
- daily routine, roosting, hibernation, lifespan
Adult
:
mate location, courtship
Mate location
Butterflies tend to have short lives. Females of most species often
have less
than a week to find a mate, copulate, search for oviposition sites,
and lay their eggs. Rapid mate location and recognition are
therefore vital - butterflies can't afford to waste time on
fruitless encounters with species other than their own.
Orange tip Anthocharis cardamines,
male, Dunsfold, Surrey, England
Butterflies can see
all the colours of the visible spectrum, plus ultra violet. Brightly coloured species such as the
Orange tip
Anthocharis cardamines are able to detect others of their
own kind from several meters away. Experiments with bright blue
Morpho species show that waving blue foil in the air
is very effective at attracting them towards observers.
Several researchers
have attempted to unravel the mysteries of visual communication /
recognition in butterflies. Magnus found that males of
Argynnis
paphia used "paper butterflies" attached
to a rotor arm to test the reaction of male
Argynnis paphia to numerous variations of colours, shapes,
sizes and patterns in paper females. A normal
paphia female is dull orange in colour, spotted with black,
and has a gentle fluttering flight.
Magnus found
however that the "ideal" female, i.e. the paper variant most
attractive to the male, was plain orange, up to 4 times the size of
the male, and had a very rapid wing flutter-frequency of about 120
Hz. This poses the question - why didn't female
paphia evolve to have huge bright
orange wings ?
The answer is
probably that the normal spotted female has
sufficient
orange content to attract the male, while a plain orange female
would be too conspicuous to predatory birds. A spotted pattern is an
effective camouflage, given that the female spends the most
important part of her life i.e. the oviposition stage, fluttering
around in the dappled sunlight of mature woodlands. A plain orange
female would attract males more easily, but would quickly be found
by birds, and would not live long enough to lay her eggs.
Papilio
machaon
- a species with an instantly recognisable pattern
While wing colour is important in the initial stages of mate
location, pattern recognition is a different matter, and only comes into
play when the butterflies are in close proximity. 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 very 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.
If butterflies relied solely on visual stimuli
for mate recognition they would waste almost all of their
short lives chasing after the wrong species, and reproduction
success would be very low indeed.
Mate recognition
During the initial
"approach" phase of mate location males will chase after almost any
small moving object including falling leaves, bees, and butterflies
of any species and either sex. After this initial contact, follow up
behaviour depends on the response of the chased object. Birds are
avoided but other butterflies are always investigated, using a
combination of visual and chemical cues. Ultra-violet patterns on
the wings often enable butterflies to recognise their own species.
When butterflies get close to each other they use chemical
messaging, in the form of pheromones, which provides additional
confirmation of species, and tells them whether they are of the same
or opposite sex.
If the pheromones
indicate that the object being pursued is a conspecific male, the
butterflies are often stimulated into aerial dogfights in which they
battle for ownership of good vantage points from which to intercept
passing females. These territorial battles can last for several
minutes, after which one male is ousted from the vicinity.
Alternatively, if
the pheromones indicate that the object being pursued is a
conspecific female, the male is stimulated into initiating
courtship. In many species exposing a female to male pheromones is
enough to initiate instant copulation, but in other species a
complex courtship ritual involving a protracted series of visual,
tactile or olfactory stimuli and responses is necessary before
copulation can take place.
Flowchart : behavioural cycle of a typical butterfly
Pupal mating
In the genus Heliconius most
species rely entirely on airborne chemicals to locate mates.
Males of
hecale, ismenius and
cydno
are attracted by pheromones to the pupae of conspecific
females. The day before emergence a female pupa will usually have
several males in close attendance. A frantic battle
takes place the instant she hatches, as the males all struggle to copulate with her, not even
allowing her time to
expand and dry her wings. In some other
Heliconius species such as
hecalesia,
hewitsoni, erato,
charithonia and
sara the males don't even wait
until the female emerges. Instead they physically break open
her pupa and copulate as soon as her genitalia are accessible.
Androconia
Males of Satyrinae, Hesperiinae, Pyrginae and Theclinae have specialised scales on their
forewings called androconia. These have sacs at their bases
containing pheromones which they disseminate into the atmosphere
via tiny hairs or plumes on the edges of the scales. The pheromones are used to
attract females and entice them to copulate.
In Danainae the androconia are on the hindwings. The males have
tufts of hair-pencils at the tips of their abdomens which they brush
against the androconial scales to collect pheromones. These are
later disseminated by expanding the tufts when in the presence of
females.
Males of several
Ithomiine species gather at "leks", where they release pheromones from hair-like androconial scales on the
upperside hindwings. These attract more males, which release
further pheromones. After a few days a lek may include a dozen
or more different Ithomiine species. Passing females are attracted by the complex fragrances, and their presence stimulates the
males to open their wings and release further pheromones that
entice the females into copulation.
Courtship rituals
The courtship
behaviour of butterflies in general is inadequately studied, but it is
clear that in most species the female will not permit the male to
copulate until he has completed an often complex ritual. This
typically begins with the male releasing airborne pheromones, which leads to
the female settling on foliage. The male might then begin a
"courtship dance" around the female, whirring his wings to
waft his pheromones across her antennae.
If the female accepts his
advances ( she may instead give him a rejection signal ),
there is often a
confirmation ritual in which contact pheromones ( cuticular
hydrocarbons ) come into play.
A well known example is the Grayling
Hipparchia semele,
in which the male
clasps the females antennae between his wings to bring them
into direct contact with his androconial scales. The Orange
Sulfur Colias eurytheme behaves
in exactly the same way.
Another example is the Wood White
Leptidea sinapis,
in which the male and female sit on a leaf, 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. The butterflies are clearly
communicating something but the ritual does not appear to instigate copulation, so the nature of
the "messages" is unclear.
Wood Whites
Leptidea sinapis
engaged in courtship ritual
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. When she
settles and opens her wings, he walks onto her hindwings, tapping
them with his antennae. The process is repeated numerous 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 beneath a small bush, where copulation
takes place.
Brimstone
Gonepteryx rhamni
males are also
commonly 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 sign that she has already
mated ( females of most butterflies only mate once ).
Brimstone
Gonepteryx rhamni,
female raises abdomen to signal rejection to male.
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 !
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 to prevent other
males from copulating.
In the case of species
which hibernate as adults, copulation occurs in the spring.
Brimstones for example
emerge in July, feed for a few weeks, and then go into hibernation
for several months. After awakening the following April, they are
mated, and then the females fly many miles, often across
inhospitable terrain, stopping to lay their eggs on any buckthorn
plants that they encounter on their travels. The butterflies thus
spread throughout the countryside, interbreeding with other
Brimstones that may have originated a considerable distance away.
The resulting high genetic diversity is probably a major factor in
the remarkable success of the species, which is able to exploit an
enormous range of habitats and climatic extremes, being found at
altitudes from sea level to 2800m, and having a range that
encompasses north Africa, the whole of Europe, and extends across
temperate Asia to Siberia and Mongolia.
Perching, patrolling, and territories
Entomologists have traditionally divided the pre-nuptial behaviour
of butterflies into two groups - those that "patrol" and those that
"perch".
Patrolling species are those where the male actively patrols a
regular or random route through it's habitat in order to locate a female.
Perching species are those where the male spends long periods
sitting on a prominent projecting leaf, or on a particular rock or
patch of ground, which it uses as a vantage point from which to intercept
passing females. These vantage points form the bases of territories,
which the males will vigorously defend against other intruding
males.
If two
males meet, they twist and turn around each other in the air, and end up spiralling upwards to a great height until
the "intruding" male
( usually a newly emerged individual which has not yet found it's
own perch )
is ousted from the territory.
A
perch is simply a vantage point from which males can get a good view
of all passing insects. Each species has it's own preferred type of
perch however -
the
Purple Emperor
Apatura iris
will perch at the top of a prominent tree, usually on a hilltop,
while the Duke of Burgundy Hamearis lucina will perch on the leaf of a bush,
typically in a small glade or at the sunny intersection of forest
paths.
In
both cases the butterflies have homed in on a spot where they have a
good view in all directions, and can survey and intercept passing
females.
In
practice, any male, of either a patrolling or perching species, will
intercept any other flying insect of similar size and colour, to
investigate it and determine whether it is a female of it's own
species. Most males will try to fly over or around a female in a
particular direction. A
Silver-washed Fritillary male
for example will loop over and under a female as she flies along a track, showering
her with pheromones. A Silver-spotted Skipper male on the other hand
will perform a figure of eight dance around a settled female,
whirring his wings to waft pheromones over her antennae.
Lysandra bellargus
copulating
pair ( female on left )
Lekking
In South American rainforests and cloudforests male Glasswings and
Tigers ( Ithomiinae ) often gather at ephemeral "leks". It
usually takes about 3-7 days for a lek to form, and it may exist for
up to 3 months, during which time numerous individual males will
come and go.
At the leks males
release pheromones from hair-like androconial scales on the
uppersides of their hindwings. These pheromones attract more males,
which release further pheromones. After a few days the lek may
contain between a dozen and several hundred individuals, comprised
of up to 20 or 30 different Ithomiine species.
Passing females are attracted to the leks by the complex fragrances.
Their presence stimulates the males to open their wings and release
other pheromones that entice the females into copulation.
10 - Daily routine, roosting, hibernation,
lifespan >>>
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