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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.
Strategies for Survival PAGE 3
 
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.
 
PAGE 1 - MATE RECOGNITION
PAGE 2 - CAMOUFLAGE and DISGUISE
PAGE 3 - APOSEMATIC COLOURATION
PAGE 4 - MIMICRY
PAGE 5 - SEXUAL DIMORPHISM
PAGE 6 - ROOSTING BEHAVIOUR
 
 
 
Aposematic coloration
 
Easily remembered patterns
 
Altinote dicaeus callianira - it's distinct pattern advertises it's unpalatability to avian predators

Some butterfly species are distasteful or toxic to birds. Such species invariably tend to "advertise" their toxic properties by the use of eye-catching and easily remembered patterns, usually comprising of bright orange markings on a contrasting black or white ground colour.

Any bird that attempts to eat one of these species will find the experience extremely unpleasant, and is likely to suffer an immediate attack of vomiting. Having tasted such a butterfly, the bird will quickly learn to associate the colour and pattern with the unpleasant experience, and will avoid eating similarly coloured butterflies in the future.

Tithorea harmonia, a conspicuously marked and highly unpalatable species from Peru.

Ocelli

Many species, such as the Peacock Inachis io are marked with conspicuous ocelli
( false eyes ) which can scare off a predator, or at least deter it long enough for the butterfly to make it's escape. The ocelli make the butterfly appear larger and "scarier" to predators, and in many cases have the effect of simulating the face of a small mammal or reptile.
 
In a study by Stockholm University, the ocelli of some Peacocks were blanked out with a marker pen. When exposed to blue tits, 13 out of 20 were attacked and eaten. A control group of Peacocks with the ocelli intact fared much better, with only a single butterfly attacked out of a group of 34.
It can be concluded that in 97 percent of encounters with blue tits, the ocelli are effective as a deterrent, and the butterfly will escape unharmed.
 
Inachis io - very beautiful to human eyes, but frightening to a small bird.

Ocelli can also serve to divert and confuse predators :

If a bird attacks a butterfly, it naturally focuses it's aim on an obvious "target". The presence of a decoy target such as a "false eye", diverts the attack away from the butterfly's body, and towards the wing borders. Usually this results in nothing more than a small chunk being pecked out of the wing, and the insect escapes virtually unharmed. It is common to find ocelli-marked butterflies with chunks taken out of their wings by birds. Butterflies are able to fly and go about their lives with quite large chunks missing from their wings, but an attack on their body would be fatal.

Sometimes the ocelli are huge, as in the neotropical Owl butterflies ( Caligo sp. ), but even the small ocelli on species such as the Gatekeeper Pyronia tithonus are enough to divert a bird attack away from the butterfly's body.

 
Caligo idomeneus,  Venezuela
 
Chloreuptychia marica, Peru
 
Pyronia tithonus - the ocelli divert bird attacks away from the butterfly's body.

Decoys to distract birds

The White-letter Hairstreak Satyrium w-album and many other Lycaenid butterflies have wings that are marked with bright streaks that lead the eye away from their head, and towards "tails" on their hindwings. The tails simulate antennae and often there is a red or black spot near the tail, which simulates an eye.

The effect is to create the illusion of a "false head", and to give the butterfly a back-to-front appearance. This is further enhanced by the butterfly's habit of immediately turning to face the other way as soon as it lands on a flower or leaf. It is also likely to dip it's real head, and raise the false head. Periodically, it oscillates the hindwings, causing the "false antennae" tails to wriggle.

An attacking bird will try to anticipate the escape route of it's prey, and aim it's attack at a point fractionally in front of the head. The "false head" fools it into aiming behind the butterfly instead. The butterfly then darts off in the opposite direction to that which the bird expects, and makes it's escape.
 
 
Satyrium w-album - false antennae and false eyes act as decoys.
 
Jamides celeno from Sri Lanka - another example of a butterfly with a "false head".

Patterns to confuse

Many butterflies have patterns which at first glance seem to serve no purpose. What for example would be the point of a striking and easily remembered pattern such as the checkerboard appearance of the Swallowtail Papilio machaon ?  One explanation could be that the butterflies might be toxic or unpalatable, and that the patterns act to warn off birds, as in the case of the Altinote and Tithorea species illustrated at the top of this page.

Watching the behaviour of butterflies often helps to reveal the answer to such riddles. The Swallowtail normally rests with it's wings closed, but if it is disturbed it suddenly flicks them open in exactly the same manner as adopted by the Peacock and other ocelli-equipped species such as Bull's-eye Silkmoths or Eyed Hawkmoths. Furthermore, when alarmed the butterfly often moves the outspread wings in a jerky and almost threatening motion, as if to deliberately draw attention to itself.

It seems likely therefore that the pattern acts either to make the butterfly appear too large to eat, or that the checkerboard design simply confuses the bird - causing it's eyes to wander all over the pattern while the bird tries to fathom out what it all means - Is it edible ? Is it dangerous ? Is it small enough to eat ? Which bit of it should I aim my beak at ? The bird may be so confused that it decides to abandon the attack, or the attack may simply be delayed long enough to allow the butterfly to escape.

The purpose of the crimson ocelli on the hindwings remains a mystery. They are not big enough to be scary, and their positioning close to the vulnerable body effectively rules out any possibility that they act as decoys or targets. The possibility that they serve some purpose in mate recognition is also ruled out, because the patterns of male and female Swallowtails are identical.
The Swallowtail Papilio machaon flicks it's wings open in a threatening manner if alarmed
 
Signalling danger to fellow butterflies

Warning colouration is generally assumed to be targeted directly at birds and other predators, but in the case of Panacea prola from Peru the purpose is quite different :

Large groups of males gather to feed on mineralised moisture on riverbanks. They bask when feeding, displaying their metallic blue uppersides, which help other passing males to locate them and home in on the feeding grounds.

A group of butterflies on the ground could easily be attacked by birds however, so the butterflies need to employ a defence strategy. Any kind of minor disturbance causes one or two butterflies to get nervous, at which point they start fanning their wings so that the bright red undersides are visible to the other butterflies.

Increased levels of nervousness cause them to fan their wings faster, which attracts the attention of further basking males, which join in the fanning activity. This "red for danger" signalling acts as a very effective alarm system, quickly alerting all Panacea in the vicinity to any perceived threat, and allowing them time to take evasive action before the threat becomes severe.

Panacea prola basks while feeding on mineralised water on a Peruvian riverbank.
 

Panacea prola fans it's wings when disturbed, displaying the bright red underside, to warn other butterflies about potential dangers.

Flash colouration

South American Morpho butterflies have brilliant iridescent blue uppersides, making them highly visible to predators as well as to potential mates. If alarmed, they immediately land, snapping their wings shut so that only the dark brown underside is visible. This alternating "now you see me, now you don't" display of brilliant uppersides and sombre underside is known as flash colouration.

A similar strategy is employed by the Red Underwing moth Catocala nupta, and by the Peruvian moth Chlorhoda albolimbata. Both have bright red hindwings that are highly visible in flight, but disappear behind cryptically coloured forewings when the moths settle. Chlorhoda has green forewings to match the foliage amongst which it hides, while Catocala rests on tree bark, and hides it's red hindwings behind mottled grey-brown forewings when it settles.

Chlorhoda albolimbata, an Arctiid moth from the Peruvian Andes.
 
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Related subjects :
 
Taxonomy  - the classification and characteristics of butterfly families and sub-families.
Lifecycle - egg, caterpillar, chrysalis, adult butterfly, courtship, reproduction.
Parasitoids and Predators - of eggs, larvae, pupae and adult butterflies.
 
Text and butterfly 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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