learnaboutbutterflies

Head


Vanessa cardui ( Nymphalidae )	Thecla betulae ( Lycaenidae )

Eyes

Butterflies and most other adult insects have a pair of spherical compound eyes, each comprising of up to 17000 facets - individual light receptors "ommatidia" with their own microscopic lenses. These work in unison to produce a mosaic view of the scene around them.

Structure

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 small cluster of 2 - 6 sensory cells, each of which is sensitive to a particular part of the visual spectrum.

The eyes of skippers ( Hesperiidae ) are more efficient than those of other butterflies because they have a clear area between the cone and the rods. This allows the light from each ommatidium to spill into neighbouring rods, which effectively increases their resolution and sensitivity. Thus skippers are able to fly speedily and very accurately from one spot to another.

This different type of eye structure is one of the reasons why taxonomists place the Hesperiidae in a different super-family to all other butterflies - the Hesperioidea.

Capabilities

Butterfly eyes are probably incapable of resolving detailed shapes or patterns although some biologists speculate that butterflies might be able to build up a composite image by means of "flicker vision".

What we know for sure is that the narrow angle seen by each ommatidium makes the compound eye extremely efficient at detecting movement, enabling butterflies to very quickly detect the approach of a predator, and take immediate evasive action.

Unlike vertebrates, which have to move their eyes / heads to scan their surroundings, butterflies have almost 360 degree vision. They can see everything at the same time, e.g. they can accurately probe into flowers in front of them, and at the same time devote equal concentration on detecting threats from behind.

In addition to their capabilities at detecting movement, butterfly eyes are also very adept at detecting slight changes in light levels. They can see polarized light, which enables them to detect the position of the sun, even when partly hidden by cloud. This enables them to find their way around their habitats, and relate their position to the sun when migrating.


A male Orange tip Anthocharis cardamines as seen by human eyes. Birds and reptiles see things in much the same way.	The same insect as it might look to another butterfly. The white areas of the wings absorb UV while the orange areas reflect it.

It is interesting to note that humans and birds perceive colours and patterns in a different way to butterflies, as the latter have the ability to detect ultra-violet as well as visible radiation. The white wings of the Large White Pieris brassicae reflect high levels of UV, and look much the same when viewed by visible or ultra-violet light. The white areas of the Orange tip Anthocharis cardamines however absorb almost all UV, while the orange wing tips are highly reflective. To another butterfly, the male Orange tip would probably appear to be a very dark insect, with highly reflective wing-tips.

Sight apparently plays little or no role in selecting plants for egg-laying, as indicated by my observation of a female Green-veined White at Stansted Forest in May 2008. The butterfly spent several minutes searching for places to lay her eggs. Every 4 - 5 seconds she would alight momentarily on a leaf, "tasting" it using olfactory sensors on her feet to check whether or not it was the correct foodplant for her offspring. Surprisingly she tested bracken, ivy and oak leaves ( all visually very different from the crucifers she needed to locate for oviposition ), a fact which appears to indicate that sight plays little or no role in selecting plants for egg-laying.

Dingy Skipper Erynnis tages ( England ) showing segmented antennae.

Antennae

From between the eyes emerge a pair of segmented antennae. These can be angled at various positions, and are best thought of as a form of radar - they are used to detect pheromones ( scents used for mate location and selection ), and guide the butterfly to the source from which they are emanating.

Essex Skipper Thymelicus lineola ( England ) frontal view of antennae.

The antennae of the Monarch Danaus plexippus have been found to be covered in about 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, were found to be sensitive both to sexual pheromones, and to the honey odour which enables them to locate sources of nectar.

The antennae of the male Fox moth Macrothylacia rubi are strongly feathered

Some moths, such as the Burnets ( Zygaenidae ) and the Cane Borers ( Castniidae ) have antennae that are clubbed, much like those of butterflies.

Male moths from other families ( e.g. Saturniidae and Lasiocampidae ) have strongly feathered antennae that are covered in tens of thousands of olfactory sensors, and can detect the scent of females from distances of up to 2km away.

Most other moths have very thin tapering antennae. In some species such as the tiny day-flying Nemophora degeerella from England, these are incredibly long, but their function appears to be unknown.

The tiny moth Nemophora degeerella has antennae 5 times the length of it's wings

In addition to their olfactory functions, butterfly antennae ( like those of ants and bees ) are also used to communicate physically - I have for example often watched Wood Whites Leptidea sinapis and Small Tortoiseshells Aglais urticae "talking" to the opposite sex by exchanging chemical messages with their antennae.

It is common also to see butterflies "antenna dipping" - periodically dabbing the tips of their antennae onto the soil or foliage on which they are sitting. In this instance they are clearly "tasting" the substrate to detect it's chemical qualities. By this means they can establish whether the soil contains essential nutrients, or whether the foliage is of the correct species for egg-laying.

Johnston's organ

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 likely that they are able to detect magnetic fields when migrating.

Labial palpi

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.

These sensors 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 attuned to the detection of 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 entomologists postulate that in addition to their olfactory functions, palpi have secondary 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 Saliana skippers and Eurybia Underleafs have average sized palpi, while Libythea Beaks and other species with prominent palpi have unremarkable proboscises.

In most butterflies the palpi are small - no more than 1-2mm long. "Beak" butterflies

( Nymphalidae : Libytheinae ) have very prominent palpi that are much longer - about 5mm, more than half as long as the antennae.

Beak butterfly Libythea myrrha ( Malaysia ), showing labial palpi projecting from head.

Proboscis

The proboscis consists of a pair of interlocking 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 into flowers to suck up the liquids on which they feed. If the proboscis gets clogged with sticky fluids, the 2 sections can be uncoupled and cleaned.

Olfactory sensors 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.

Anteos menippe ( Peru ) with proboscis extended to imbibe mineralised moisture.

Feeding behaviour

In temperate zones most butterflies obtain their sustenance from flowers, but there are exceptions - the male Purple Emperor for example never visits flowers; it feeds instead on liquefied minerals which it obtains from dung, carrion, urine-soaked ground, tree sap, rotting fruit, and the aphid secretion "honey dew".

In tropical regions it is common to see Swallowtails, Acraeas, Heliconiines and Pierids visiting flowers, but the majority of species from other families follow the behaviour described above for the Purple Emperor.

Often large numbers of butterflies ( e.g. male Papilionidae, Pieridae and Limenitidinae ) gather to filter-feed, drinking mineralised water from puddles or damp sand. Butterflies of other subfamilies such as Charaxinae and Apaturinae however are more commonly attracted to dung, rotting fruit or carrion.

The carrion feeders vary enormously in their choice of foodstuff - I have often seen Glasswings feeding on the decomposing corpses of flies, and have seen the Blue Doctor Rhetus periander feeding on a road-kill giant tarantula in Venezuela. In Ecuador I once found scores of high-altitude Satyrines including Junea, Lasiophila and Lymanopoda feeding on a snake corpse.

In England carrion-feeding is less common than in the tropics, but I once found 6 male Purple Emperors Apatura iris feeding at the carcass of a roe deer that was floating in an open cesspit in a Hampshire thicket. The butterflies were so stupefied 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 Ithomiines ( Tiger-mimics, Glasswings ) and Skippers form associations with ant-bird colonies. The birds follow marauding soldier ant armies, feeding on insects which scatter as the ants approach. In turn the Skippers and Ithomiines follow the ant-birds, feeding on their liquefied droppings.

The feeding behaviour of butterflies is discussed in greater detail in the individual species accounts, which can be accessed from the galleries or the Species Index.

The "BD" butterfly Callicore cynosura, imbibing dissolved minerals from the surface of a damp rock on the shore of an Amazonian tributary.

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Butterflies of the World - Lifecycle, Ecology, Taxonomy, Conservation, Photography, Butterfly Holidays, Photo Galleries, Book Reviews and more......... About me \| Contact me \| Home Butterfly Study Holidays Trip Reports Butterfly Diary - latest sightings Where to find butterflies Frequently Asked Questions Test Your Knowledge Strange but true ! Taxonomy & Evolution Anatomy Lifecycle Ecology Survival Strategies The Enemies of Butterflies Migration & Dispersal Habitats in Britain Rainforests World Butterfly Census Butterfly Books Butterfly Art Gallery Butterfly photography Butterflies of the British Isles Butterflies of the French Alps Butterflies of Amazonia Butterflies of the Andes Butterflies of Malaysia & Borneo Butterflies of West Africa Species index Subject index Glossary Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.
		Butterfly Anatomy PAGE 1 PAGE 1 - HEAD PAGE 2 - THORAX / ABDOMEN PAGE 3 - WINGS Head eyes \| antennae \| Johnston's organ \| labial palpi \| proboscis \| feeding Vanessa cardui ( Nymphalidae ) Thecla betulae ( Lycaenidae ) Eyes Butterflies and most other adult insects have a pair of spherical compound eyes, each comprising of up to 17000 facets - individual light receptors "ommatidia" with their own microscopic lenses. These work in unison to produce a mosaic view of the scene around them. Structure 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 small cluster of 2 - 6 sensory cells, each of which is sensitive to a particular part of the visual spectrum. The eyes of skippers ( Hesperiidae ) are more efficient than those of other butterflies because they have a clear area between the cone and the rods. This allows the light from each ommatidium to spill into neighbouring rods, which effectively increases their resolution and sensitivity. Thus skippers are able to fly speedily and very accurately from one spot to another. This different type of eye structure is one of the reasons why taxonomists place the Hesperiidae in a different super-family to all other butterflies - the Hesperioidea. Capabilities Butterfly eyes are probably incapable of resolving detailed shapes or patterns although some biologists speculate that butterflies might be able to build up a composite image by means of "flicker vision". What we know for sure is that the narrow angle seen by each ommatidium makes the compound eye extremely efficient at detecting movement, enabling butterflies to very quickly detect the approach of a predator, and take immediate evasive action. Unlike vertebrates, which have to move their eyes / heads to scan their surroundings, butterflies have almost 360 degree vision. They can see everything at the same time, e.g. they can accurately probe into flowers in front of them, and at the same time devote equal concentration on detecting threats from behind. In addition to their capabilities at detecting movement, butterfly eyes are also very adept at detecting slight changes in light levels. They can see polarized light, which enables them to detect the position of the sun, even when partly hidden by cloud. This enables them to find their way around their habitats, and relate their position to the sun when migrating. A male Orange tip Anthocharis cardamines as seen by human eyes. Birds and reptiles see things in much the same way. The same insect as it might look to another butterfly. The white areas of the wings absorb UV while the orange areas reflect it. It is interesting to note that humans and birds perceive colours and patterns in a different way to butterflies, as the latter have the ability to detect ultra-violet as well as visible radiation. The white wings of the Large White Pieris brassicae reflect high levels of UV, and look much the same when viewed by visible or ultra-violet light. The white areas of the Orange tip Anthocharis cardamines however absorb almost all UV, while the orange wing tips are highly reflective. To another butterfly, the male Orange tip would probably appear to be a very dark insect, with highly reflective wing-tips. Sight apparently plays little or no role in selecting plants for egg-laying, as indicated by my observation of a female Green-veined White at Stansted Forest in May 2008. The butterfly spent several minutes searching for places to lay her eggs. Every 4 - 5 seconds she would alight momentarily on a leaf, "tasting" it using olfactory sensors on her feet to check whether or not it was the correct foodplant for her offspring. Surprisingly she tested bracken, ivy and oak leaves ( all visually very different from the crucifers she needed to locate for oviposition ), a fact which appears to indicate that sight plays little or no role in selecting plants for egg-laying. Dingy Skipper Erynnis tages ( England ) showing segmented antennae. Antennae From between the eyes emerge a pair of segmented antennae. These can be angled at various positions, and are best thought of as a form of radar - they are used to detect pheromones ( scents used for mate location and selection ), and guide the butterfly to the source from which they are emanating. Essex Skipper Thymelicus lineola ( England ) frontal view of antennae. The antennae of the Monarch Danaus plexippus have been found to be covered in about 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, were found to be sensitive both to sexual pheromones, and to the honey odour which enables them to locate sources of nectar. The antennae of the male Fox moth Macrothylacia rubi are strongly feathered Some moths, such as the Burnets ( Zygaenidae ) and the Cane Borers ( Castniidae ) have antennae that are clubbed, much like those of butterflies. Male moths from other families ( e.g. Saturniidae and Lasiocampidae ) have strongly feathered antennae that are covered in tens of thousands of olfactory sensors, and can detect the scent of females from distances of up to 2km away. Most other moths have very thin tapering antennae. In some species such as the tiny day-flying Nemophora degeerella from England, these are incredibly long, but their function appears to be unknown. The tiny moth Nemophora degeerella has antennae 5 times the length of it's wings In addition to their olfactory functions, butterfly antennae ( like those of ants and bees ) are also used to communicate physically - I have for example often watched Wood Whites Leptidea sinapis and Small Tortoiseshells Aglais urticae "talking" to the opposite sex by exchanging chemical messages with their antennae. It is common also to see butterflies "antenna dipping" - periodically dabbing the tips of their antennae onto the soil or foliage on which they are sitting. In this instance they are clearly "tasting" the substrate to detect it's chemical qualities. By this means they can establish whether the soil contains essential nutrients, or whether the foliage is of the correct species for egg-laying. Johnston's organ 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 likely that they are able to detect magnetic fields when migrating. Labial palpi 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. These sensors 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 attuned to the detection of 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 entomologists postulate that in addition to their olfactory functions, palpi have secondary 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 Saliana skippers and Eurybia Underleafs have average sized palpi, while Libythea Beaks and other species with prominent palpi have unremarkable proboscises. In most butterflies the palpi are small - no more than 1-2mm long. "Beak" butterflies ( Nymphalidae : Libytheinae ) have very prominent palpi that are much longer - about 5mm, more than half as long as the antennae. Beak butterfly Libythea myrrha ( Malaysia ), showing labial palpi projecting from head. Proboscis The proboscis consists of a pair of interlocking 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 into flowers to suck up the liquids on which they feed. If the proboscis gets clogged with sticky fluids, the 2 sections can be uncoupled and cleaned. Olfactory sensors 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. Anteos menippe ( Peru ) with proboscis extended to imbibe mineralised moisture. Feeding behaviour In temperate zones most butterflies obtain their sustenance from flowers, but there are exceptions - the male Purple Emperor for example never visits flowers; it feeds instead on liquefied minerals which it obtains from dung, carrion, urine-soaked ground, tree sap, rotting fruit, and the aphid secretion "honey dew". In tropical regions it is common to see Swallowtails, Acraeas, Heliconiines and Pierids visiting flowers, but the majority of species from other families follow the behaviour described above for the Purple Emperor. Often large numbers of butterflies ( e.g. male Papilionidae, Pieridae and Limenitidinae ) gather to filter-feed, drinking mineralised water from puddles or damp sand. Butterflies of other subfamilies such as Charaxinae and Apaturinae however are more commonly attracted to dung, rotting fruit or carrion. The carrion feeders vary enormously in their choice of foodstuff - I have often seen Glasswings feeding on the decomposing corpses of flies, and have seen the Blue Doctor Rhetus periander feeding on a road-kill giant tarantula in Venezuela. In Ecuador I once found scores of high-altitude Satyrines including Junea, Lasiophila and Lymanopoda feeding on a snake corpse. In England carrion-feeding is less common than in the tropics, but I once found 6 male Purple Emperors Apatura iris feeding at the carcass of a roe deer that was floating in an open cesspit in a Hampshire thicket. The butterflies were so stupefied 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 Ithomiines ( Tiger-mimics, Glasswings ) and Skippers form associations with ant-bird colonies. The birds follow marauding soldier ant armies, feeding on insects which scatter as the ants approach. In turn the Skippers and Ithomiines follow the ant-birds, feeding on their liquefied droppings. The feeding behaviour of butterflies is discussed in greater detail in the individual species accounts, which can be accessed from the galleries or the Species Index. The "BD" butterfly Callicore cynosura, imbibing dissolved minerals from the surface of a damp rock on the shore of an Amazonian tributary. NEXT >> Related subjects : Taxonomy - the classification and characteristics of butterfly families and sub-families. Lifecycle - egg, caterpillar, chrysalis, adult butterfly, courtship, reproduction. Text and photographs protected by Copyright © Adrian Hoskins 2007-2008, and must not be reproduced or published in part or in whole elsewhere in any form without written permission from Adrian Hoskins. Breach of copyright will be pursued by litigation. 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