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Strategies for
Survival
PAGE 1
Butterflies
occur in an incredible variety of sizes, shapes, colours and
patterns. Each design serves a dual role. Firstly it must act as a
"badge", identifying the butterfly to potential mates.
Secondly, and perhaps more importantly,
it must function to protect the butterfly from predators, either by
using camouflage, warning coloration, mimicry or transparency.
It is possible of
course to read too much into the "colour for survival" theme.
There does not have to be a survival-related reason for every
nuance of pattern or colour. After all, what possible difference
could it make if a caterpillar has a brown head instead of a black
one ? Having said this however it is quite obvious that a
butterfly that is camouflaged as a dead leaf has a much higher
chance of survival than one that is not.
PAGE 1 - MATE RECOGNITION
PAGE 2 - CAMOUFLAGE and
DISGUISE
PAGE 3 - APOSEMATIC
COLOURATION
PAGE 4
- MIMICRY
PAGE 5
- SEXUAL DIMORPHISM
PAGE 6 - ROOSTING BEHAVIOUR
PAGE 7 - SEASONAL DIMORPHISM
Mate recognition
Butterflies
generally have short lives, and need to be able to quickly locate
potential mates. Many species lose
their attraction to the opposite sex within a day or two of
emergence because their pheromones become exhausted. Rapid mate recognition is
therefore vital.
The first stage in the recognition process
consists of intercepting any flying object of roughly the same size
and colour as their own species - in
the neotropics for example it is easy to attract
Morpho butterflies by waving a
piece of blue foil in the air.
Many of the more conspicuously coloured species such as Whites
and Sulphurs can detect each other from several metres away, but the
smaller and duller species need to be much closer - perhaps within
one or two metres.
Purple Emperor Apatura
iris, male
In many genera such as
Apatura,
Morpho
and
Doxocopa
the wings of males have an extremely reflective blue sheen, whereas
the females are sombre in colour. During flight the wings of the
males glint brilliantly in the sunshine, and probably play a major
role in mate location and recognition.
Once initial contact has been made, a
combination of olfactory and visual factors hold the interest of
both sexes as a precursor to the courtship ritual. Visual stimuli
include holding the wings or body at particular angles, flicking the
wings, or simply displaying the patterns by opening the wings.
During the courtship process a
series of exchanges take place during which olfactory and visual
stimuli trigger a particular response. A
"wrong" response might indicate that the potential mate was not of
the same species, or was unwilling to mate - females of many Pierids
for example signal an unwillingness to mate by raising their abdomen
and outspreading their wings.
A "correct" response invariably
triggers an array of further visual, olfactory and tactile stimuli,
each leading to a set response which confirms that
both butterflies are of the same species, of the opposite sex, and
willing to mate. In some species this process is very brief, but in
others such as the Small Tortoiseshell
Aglais urticae,
it is protracted and may take several hours during which the male
doggedly follows the female from place to place, persuading her to
copulate.
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Small Tortoiseshell Aglais urticae |
Male
butterflies will usually intercept both sexes of their own
species. The purpose of male-male sorties is to challenge and oust an
intruding male from the "territory" of another, thereby increasing
the territory owner's chances of success with any female that
passes by.
Males also
"know" that they can often find food by following other males :
In tropical
regions males of many species visit sandbanks and damp paths to
indulge in "mud-puddling". Their purpose is to imbibe mineralised water,
from which they obtain vital salts. These are passed to females
during copulation, and are believed to be essential for the
production of fertile eggs. Females do not normally mud-puddle,
they feed instead on nectar.
Typically just one or two males
will chance upon a suitable
feeding spot, but other butterflies flying past
seem able to recognise their brethren on the ground, and swoop
down to join them. The bright patch of colourful butterflies
quickly becomes a magnet to every passing male of the same
species.
Sometimes
several different species may be present at these feeding places.
In these circumstances one might expect each species to be spread
randomly within a large group, but in fact each butterfly polarises very strongly to it's own brethren, so that each species
congregates as a discrete group. In calm weather the butterflies
in each group are positioned randomly, but on riverbanks there is
usually a constant gentle breeze, so all the butterflies in each
group tend to face into the breeze as this way they are less
likely to be blown about and lose their feeding spot to a
competitor.
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Dryas iulia,
Peru. A single male on the ground quickly attracts others of the
same species. |
More information about courtship, feeding and other
forms of adult behaviour can be found on the
Lifecycle and
Anatomy
pages, and in the individual
species accounts.
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