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Butterfly Anatomy
PAGE 2
PAGE 1 - HEAD
PAGE 2 -
THORAX / ABDOMEN
PAGE 3 -
WINGS
Thorax and Abdomen
legs
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wing muscles
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respiration
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digestion
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reproduction
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The middle
section of the body, the thorax, is best thought of as a muscular
anchor to which the head, legs, segmented abdomen,
and wings are attached. |
Legs
All adult
butterflies have 3 pairs of jointed legs, although in the
Nymphalidae the front pair are reduced to
brush-like stumps and modified as chemoreceptors.
The tibia on the forelegs of Pieridae, Hesperiidae, Papilionidae and Lycaenidae are often equipped with a flexible spur
through which the antennae can be drawn for cleaning.
The tibia of each leg also houses a subgenual
organ, which detects and amplifies small vibrations. This allows
butterflies to always be very alert to ground vibrations caused
by the approach of an animal or bird, and ready to instantly respond.
In most cases butterflies take flight, but some species such as the
Peacock
Inachis io
and
Bullseye moths
Automeris randa
react by
suddenly flashing open their wings to display "false eye" markings
that startle the predator.
The legs,
particularly the middle pair, are covered in olfactory sensors that
enable butterflies to "taste" any substrate on which they land. Females of most species tend to take a great deal of time flitting
from one leaf to another, momentarily using their feet to taste the chemicals on the
surface of the foliage. They are able to instantly analyse the
chemicals to determine whether the plant is of the right species for
egg-laying.
The Wood White Leptidea sinapis,
like all Pieridae species, has
6 fully functional legs. Males of some Pieridae such as the
Brimstone Gonepteryx rhamni often
rest with the forelegs held tight against the body, so at first
glance can appear to have only 4 legs.
Marsh Fritillary
Euphydryas aurinia. In
common with all Nymphalidae species, both sexes have only 4
functional legs. The forelegs are reduced to stumps used as
chemoreceptors.
Wing muscles
Within the thoracic cavity of flying insects
are very powerful muscles which lever on the wings. Their
rapid expansion and contraction causes the wings to lift and fall at
rates of up to 1000 beats per second in bees and
hoverflies, and about 200 beats per second in hawkmoths. The rapid
wing beats and an ability to alter the angle of the wings allows
hawkmoths to hover, and even to fly backwards.
Amongst the butterflies, Skippers
have the most rapid wing beats, buzzing and whirring from place to
place beating their wings at a rate of
about 20 beats per second. Swallowtails, Pierids and Satyrines manage
only about 5-10 beats per second. Slower still are the Ithomiines
which have very deep beats at about 4 per second, but the slowest of
all are the Caligo Owl
butterflies which struggle to achieve more than 2 or 3 beats per
second and flap about quite awkwardly.
Abdomen
The abdomen contains the digestive
system, breathing apparatus, a long tubular heart, and the sexual organs.
The abdominal exoskeleton is multi-segmented. Each of the 10 segments
is comprised of a ring of a
hard material called chitin. The segments are linked by flexible tissues,
allowing the abdomen to bend, a necessity for copulation and
egg-laying.
Respiration
On the sides of
each segment are microscopic holes called spiracles, through which
air enters and leaves the body. Slight rhythmic movements of the
body, coordinated with the opening and closing of the spiracles,
causes air to be drawn into tiny lung-like sacs, and later expelled.
Digestion
Butterflies feed exclusively on liquids which may according to
species include nectar, dissolved pollen, mineralised water,
liquefied dung, urine, sweat, bodily fluids from decomposing animal
corpses, and in some cases even tears from the eyes of alligators !
After digestion and extraction of proteins and other minerals the
waste matter is
expelled from the anus either in liquid form, or as tiny faecal pellets.
Reproductive organs
The genitalia (
reproductive organs ) are at the tip of the abdomen. Each
species has uniquely shaped genital armature - the male "key" only fitting
the correct female "lock". Because the armature is unique to each
species,
taxonomists
have traditionally relied heavily on
microscopic examination of genitalia to determine species and
their relationship with other taxa. The advent of DNA analysis and
advances in phylogenetics however now mean that genitalia study is
just one of many techniques adopted.
Females are
equipped with an ovipositor, used to release and deposit the
fertilised eggs. In most species this is short and not normally
visible, but in certain moths it is modified into a long
"sting-like" tube so that the eggs can be inserted into chinks in
the bark of trees.
The females of
many moths also have a scent-emitting organ located at the tip of
the abdomen.
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