1 - Head
2 - Thorax - legs & abdomen
3 - Wings
venation & scales
- Wing scales - scanning electron microscope images
- Hearing organs, flight,
Antennae, eyes, palpi, proboscis
Butterflies and most other adult insects have a pair of spherical
compound eyes, each comprising of up to 17000 "ommatidia" - individual
light receptors with their own microscopic lenses. These work in
unison to produce a mosaic view of the scene around them.
Each ommatidium consists of a
cornea and cone, which together function as a lens. Emerging from
the back of each cone is a rod down which light travels to reach a
cluster of 2-6 sensory cells, each of which is sensitive to a
particular part of the visual spectrum.
The eyes of Skippers are different
from those of other butterflies. They have a space between the cones
and rods which allows light from each ommatidium to spill into
neighbouring rods, effectively increasing their resolution and
sensitivity. As a result Skippers can fly very accurately from one
spot to another. This different type of eye structure is one of the
reasons why taxonomists place them in a different super-family to
all other butterflies - the Hesperioidea.
The laws of optics
it's likely that everything from about one centimetre to 200 metres
will be rendered in sharp focus by butterflies, as their ommatidia
are of very short focal length.
butterfly's brain can instantly detect whether the image formed by
each ommatidium is dark or light. If a predator approaches or if the
butterfly moves its head a tiny fraction, the amount of light
hitting each receptor changes instantly because of it's very narrow
angle of view. This sensitivity to changes in its surroundings means
that a butterfly is
extremely efficient at detecting movement and at gauging the
distance of an approaching predator, enabling it to take immediate
The sensitivity to changes in their visual field,
combined with a high flicker-vision frequency of about 150 images
per second, may also help butterflies to piece together the
thousands of elements of the mosaic image produced by the compound
eye. It is not known whether butterflies and other insects are able
to merge these mosaic elements into a single image. If are able to
do so, it would render them capable of distinguishing patterns at
need to move their eyes and heads to scan their surroundings, but
the compound eyes of butterflies provide them with almost 360 degree
vision. They can see everything at the same time, so they can
accurately probe into flowers in front of them, and at the same time
devote equal concentration to detecting threats from behind.
Butterflies can see polarized light, enabling
them to determine the position of the sun, even when it is partly
hidden by cloud. This lets them relate their position to the sun and
use it as a compass when moving around their habitats.
birds perceive colours in a different way to butterflies, as the
latter are ultra-sensitive to UV as well as visible radiation.
Flowers have ultra-violet patterns that are invisible to humans but
which can be recognised by butterflies. These UV patterns guide
butterflies to the source of nectar in much the same way that runway
lights guide an aircraft in to land.
butterflies dyed orange, red, green, blue and black have
shown that females don't discriminate between males of different
colours. Most biologists agree that visible colours and patterns are
NOT used for butterfly-to-butterfly communication. Their primary
function is to convey survival-related signals to birds ( i.e.
camouflage, aposematic colour, mimetic patterns etc ).
communicate with each-other visually, but they use a "private
channel" of ultraviolet patterns which are overlaid on the visible
patterns, and cannot be seen by vertebrates. They enable butterflies
to recognise conspecifics during the initial "approach" phase of
mate location. It has been proven by experimentation that males
which have had their UV-reflecting patterns obliterated suffer a
significant drop in mate-location success.
As well as being
sensitive to UV patterns, butterflies are also alert to the
iridescent colours produced when sunlight refracts from the wings of
other butterflies. Many species have also
evolved selective colour response, i.e. they are "tuned" to react to
colours that are dominant in the wing patterns of their own species.
sensitive to red,
Morpho helenor which reacts very
strongly to blue,
and Philaethria dido
which is responsive to green.
will intercept and chase any insect of approximately the same size
and colour as the female of their own species during the approach
phase of mate-location. Experiments using dummy cardboard females
have however shown that males respond equally to square, circular,
triangular, or butterfly-shaped dummies.
Females of some
species however seem capable of recognising plants purely on the
basis of leaf-shape and colour. This ability varies from one species
to another, and is most highly developed in monophagous butterflies
- those whose larvae will only eat one type of plant.
butterflies ( those which utilise several families or genera of
larval foodplant ) tend to rely almost exclusively on chemical cues.
I have e.g. often observed
Pieris napi females searching for
oviposition sites. They
alight momentarily on various plants, sampling each by puncturing
the leaf cuticle with spurs on the legs, to release chemicals in the
leaf which are then tasted using the olfactory receptors in the
feet. Leaves which were tested included
bracken, ivy and oak leaves, all of which are very different in
shape from the crucifers needed for oviposition. This appears to
indicate that in this species sight plays little or no role in
selecting plants for egg-laying.
Vision in nocturnal moths
Deilephila elpenor have been studied to
determine whether or not nocturnal moths can perceive colour. It
seemed unlikely, but Kelber et al found that this species has 9
light receptors in each ommatidium ( compared to between 2-6 in
butterflies ); and used behavioural experiments to prove that the
moths can discriminate coloured stimuli at intensities corresponding
to dim starlight.
are unable to blink, so need other ways to protect their eyes. In
many butterflies and moths the eyes are shielded by the labial
palpi, which act as dust filters. Butterflies
in the Satyrine genus Lethe have a
dense layer of fine setae or "hairs" on their compound eyes.
Studies by the author of these
butterflies in Sri Lanka and Borneo indicate that they are strongly
attracted to wet dung, and spend long periods probing into it. It
seems plausible therefore that the setae could function in the same
way as a cat's whiskers, acting as tactile sensors that warn them
when their eyes get too close to the dung, which would blind them if
it stuck to the eye surface.
between the eyes emerge a pair of segmented antennae. These can be
voluntarily angled at various positions, and are best thought of as
a form of radar. They have many functions including pheromone
detection, which is used for mate location and recognition.
( England ) frontal view of antennae ©
The antennae of Monarchs
Danaus plexippus are covered in over
16000 olfactory ( scent detecting ) sensors - some scale-like,
others in the form of hairs or olfactory pits.
The scale-like sensors, which number about 13700
in total, are sensitive to sexual pheromones, and to the honey odour
which enables them to locate sources of nectar.
antennae, like those of ants and bees may also used to communicate
physically - e.g. it is common to see male Small
Tortoiseshells Aglais urticae drumming
their antennae on the hindwings of females during courtship,
possibly to "taste" pheromones on the female's wings. Similar
activity can be found in Wood Whites Leptidea
sinapis and many other species.
"antenna dipping" - dabbing the antennal tips onto soil or leaves.
In this case they are sampling the substrate to detect it's chemical
qualities. They do this to establish whether soil contains essential
nutrients. Male butterflies often drink mineralised moisture to
obtain sodium, which they pass to the females during copulation.
Differences between butterfly and
Butterfly antennae are always clubbed at the tips. In most butterfly
subfamilies e.g. Nymphalinae, Heliconiinae and Pierinae the shaft is
straight and the club very pronounced, but in the Ithomiinae the
antennae thicken progressively towards the tip. The clubs of
Skippers ( Hesperiidae ) taper to a fine point and are hooked at the
tip, but most other butterflies have rounded ends to the clubs.
including Burnets ( Zygaenidae ) and Cane Borers ( Castniidae ) also
have antennae that are clubbed just like those of butterflies. This
is one of many reasons why the "convenience" division of Lepidoptera
into butterflies and moths is difficult to justify scientifically.
( Zygaenidae ), England. Burnet moths have
antennae that are clubbed even more than those of true butterflies ©
Male moths from the Saturniidae,
Lasiocampidae and a few other families
have plumed "pectinate" antennae which are covered in tens of
thousands of olfactory sensors, and can detect the scent of females
from distances of up to 2km away. The females have no need to detect
pheromones, so their antennae, although similar in structure, have
very much shorter plumes.
of male American Oak Silkmoth
© Emily Halsey
At the base of the
antennae is a "Johnston's organ". This is covered in nerve cells
called scolopidia, which are sensitive to stretch, and are used to
detect the position of the antennae, as affected by gravity and wind.
Thus they are used to sense orientation and balance during flight, and
enable the butterflies to finely adjust their direction or rate of
ascent / descent. It is also thought possible that they are able to
detect magnetic fields when migrating.
Protruding from the front of the head are
a pair of small projections called labial palpi, which are covered in
olfactory ( scent detecting ) sensors. Similar sensors are also
located on the antennae, thorax, abdomen and legs.
are present in a variety of forms, and it is likely that each type
fulfils a different role. Sensors on the antennae for example might be
"tuned" to locate sexual pheromones, while those on the legs may be
sensitive to chemicals exuded by larval foodplants. Logic would
indicate that those on the labial palpi and proboscis, due to their
position, might be tuned to detect adult food sources such as nectar,
urine, carrion or tree sap.
Alternatively it is
possible that they might function to detect the "smell" of air which
emanates from particular locations - incoming dry desert air for
example might be detected and act as a trigger to stimulate migration.
Some biologists argue that in addition to their olfactory functions,
palpi have other functions such as shielding the proboscis. Logically
this would mean a short proboscis would be associated with small
palpi, and a long proboscis associated with larger palpi. In fact this
is not the case - species with very long proboscises, such as
skippers and Eurybia Underleafs
have average sized palpi, while
Beaks and other species with prominent palpi have unremarkable
Another theory is that the
palpi may serve as dust filters to protect the surface of the eyes.
DeVries states that the most well developed palpi are found in
butterflies which feed as adults on rotting fruit or dung where there
is a greater probability of soiling the eyes or becoming infested with
mites. This theory however doesn't hold true for
Libythea Beak butterflies
which have extremely long palpi but which feed at flowers, or in the
case of males at mineralised moisture at the edge of puddles.
showing labial palpi projecting from head ©
proboscis consists of a pair of interlocking c-section channels that
when linked together form a tube, much like a drinking straw. This
tube can be coiled up like a spring for storage, or extended to
enable the butterfly to reach deep into flowers to suck up nectar.
If the proboscis gets clogged with sticky fluids the 2 sections can
be uncoupled and cleaned.
near the tip of the proboscis and in the food canal, together with
similar sensors on the tarsus and tibia of the legs, enable
butterflies to "taste" nectar, pollen, dung and minerals.
Callicore cynosura, using its proboscis as a drinking straw
to imbibe dissolved minerals from the surface of a damp rock on the
shore of an Amazonian tributary ©
temperate zones most butterflies obtain their sustenance by sucking
nectar from flowers. There are exceptions however - male Purple
Emperors Apatura iris for example never
visits flowers; they feed entirely on fluids which they obtain from
sources including dung, carrion, urine-soaked ground, tree sap and
honeydew ( aphid secretions ).
In the Alps and Pyrenees mountain ranges of
Europe males of many species, particularly
Cupido & Mellicta often
aggregate in groups of several dozen ( and sometimes several hundred
) to imbibe mineralised moisture from the edges of puddles,
urine-soaked ground or cattle dung. This phenomenon is common in
alpine regions throughout the northern hemisphere.
In the tropics the
majority of males from all families follow the behaviour described
above for the Purple Emperor.
Females of some species appear not to
feed at all, and rely on proteins and amino acids transferred via
the sperm of males during copulation. In the case of Papilionidae,
Pieridae and Lycaenidae however females commonly obtain sustenance
from flower nectar.
In Central &
South America female Heliconius
visit Lantana and various other flowers
for nectar. They also sequester pollen from
Psiguria, Anguria and
Gurania flowers in the
collected from the flowers is processed by the females to extract
amino acids which increase longevity and enable them to produce eggs
for up to 9 months.
The butterflies have acquired the ability to learn and remember the
locations of individual pollen plants. They visit these every day,
following a predefined circuit through the forest.
Phoebis argante and
Rhabdodryas trite aggregating to imbibe
moisture, Peru ©
Swarms of butterflies, e.g. males of Eurema,
Callicore habitually aggregate on river beaches to
filter-feed, drinking mineralised water from damp sand. Numerous
other species such as Doxocopa,
Rhetus & Caria
also gather in lesser numbers in similar situations.
Males from subfamilies
such as Charaxinae and Apaturinae are commonly attracted to dung,
rotting fruit or carrion.
estimated that at least 40 percent of all Nymphalidae in Costa Rica
feed exclusively on rotting fruit.
The carrion feeders vary enormously in their
choice of foodstuff. In Ecuador I have commonly seen Glasswings
feeding on the decomposing corpses of robber flies, and in Venezuela
I watched a male
sucking fluids from the corpse of a giant tarantula.
At Pululuhua Crater in
Ecuador I once found scores of high-altitude Satyrines including
Junea feeding on a snake corpse; and at
Maquipucuna Cloudforest I stumbled upon a stunning
Necyria avidly feeding on the corpse of
In temperate regions carrion-feeding is far less
common than in the tropics, but
fondly remember finding
6 male Purple
feeding at the
carcass of a deer that was floating in an open cesspit in
butterflies were so
by their unsavoury meal that 2 of them remained on the carcass as I
lassoed a rope around the antlers and hauled it to the edge of the
cesspit to take photographs !
In the rainforests of South America many butterflies form
associations with ant-bird colonies. The birds follow armies of
marauding soldier ants, feeding on insects that scatter as the ants
approach. In turn the butterflies follow the ant-birds, feeding on
their liquefied droppings. Biologists studying butterflies in
rainforests commonly place tiny wads of dampened white tissue,
designed to simulate bird-droppings, on leaves to attract
butterflies from the families Hesperiinae and Ithomiinae.
The feeding behaviour of butterflies is discussed in greater detail
in the individual species accounts, which can be accessed from the
galleries or the