Conventional wisdom has it that the ‘tails’ seen at the end of the hindwings of many butterflies, particularly lycaenids (the ‘blues’), are serving to mimic antennae, and together with eyespots located on the undersides of the hindwings, create the impression of a head. These ‘false heads’ are therefore, a form of reverse mimicry. They serve to deflect attacks by predators to a more expendable end! It’s one thing to lose a bit of wing; quite another to lose your head! Another term – symmetry deception – has been used to describe the illusion created by the shapes and colours which fool an observer (i.e. a would be predator) as to the true front or back end of the organism. Indeed, it might just be enough to cause consternation in the mind of the predator! “What the heck is this thing; I’ll find something else to eat!”
It has to be said that in many cases, the image of the ‘false head’ created at the back end of a butterfly is a rather poor mimic (or reconstruction) of the front end. To our eyes at least, the two ends are not always a close match; far from it. This is particularly so in the case of butterflies with long fluffy tails. If the purpose of the tails is to create an exact likeness of the antennae at the front of the organism, they are not doing a very good job. If their evolutionary function were to create an exact replica of the antennae, surely forces of selection would have acted to produce a much more accurate feature. Since that is not the case for many families of such butterflies – e.g. long-tailed hairstreaks – something else must be going on.
Scientific evidence for the effectiveness of these ‘false head’ markings on butterflies is still fairly thin. Lycaenid species with the most convincing – to a human (such as investigator Robert K. Robbins who studied this) – ‘false head’ patterns, had significantly more bird peck marks at the hind (i.e. false head) end. The peck marks were taken as evidence of an unsuccessful attack by a predator, but what is not known – and perhaps can never be known – is how many butterflies received a peck, but instead of escaping, got eaten! In other words, is a peck mark a reliable indicator of a successful strategy (false head mimicry working to enable the individual to make an escape) or is it just an indication that these individuals made a lucky escape? There is some evidence to suggest that parts of the wing at the tail end break off more easily. Butterflies can easily continue their lives with a little – sometimes a lot – of damage to the wing. The following photo shows a peck mark right on the eyespot. It’s hard not to jump to the conclusion that the false head did its job and the butterfly lived to see another day!
Some species have what most people would agree are tails which are very antenna-like, at the hind end. For example, the Common Tit (Hypolycaena erylus himavantus) has thin black and white tails which it moves around in a very convincing manner.
The tails are not exactly like the antennae (which are striped) but they have white tips and presumably they are good enough to do the job, i.e. of fooling a predator. The following photograph shows the front end – the real head! – of this butterfly.
The other end of the butterfly is shown below. It is possible to imagine how the eyespots and tails could conjure up an image of a head, but the butterfly is not trying to fool us (humans), but its own predators; who might see the world in a different way. The fact that these false head markings are so common and widespread, from continent to continent – is reason enough to think that they work well. Coloured scales (on the eyespots) and wiggly tails are probably physiologically costly to produce and maintain, and a butterfly would not waste all that energy if they had no use or purpose. Or so it seems to me?
Here’s another example of what seems to me to be a rather convincing ‘false head’, this time on the small Gram Blue (Euchrysops cnejus cnejus) butterfly (below). It is also quite possible that butterflies have the ability to effectively change the shape of the false head – by moving their hind wings back and forth – depending on how close a predator, such as a bird, gets to them.
Very few examples of mimicry are absolutely perfect – i.e. looking exactly like the model – and some are rather poor, what biologists call ‘imperfect mimicry’. No one know for sure, but one reason why so-called imperfect mimics might work, and persist in nature, is that the predators do not make fine distinctions. In other words, in the split second when a bird, lizard to spider decides, in this case, which end of the butterfly to grab hold of, it is probably just using a generalised mental model of a ‘butterfly head with antennae’. It is not saying to itself, “that looks a bit like an antenna but I’m not convinced”! It just instinctively knows that butterflies and other insects have long, thin wiggly bits at the head end! And it is this lack of precision – there is not the time to ponder – that probably maintains the imperfect mimicry. The tails at the hind end of the Fluffy Tit (Zeltus amasa amasa) – shown below – do not look to me anything like the antennae at the front end.
The fact that these tails are so dissimilar to the antennae suggests to me that there may be something else going on? Perhaps there is no attempt at mimicry, other than in their movement, but rather they are simply decoys, drawing the attention of the predator away from the body of the butterfly?
In conclusion, it’s hard to know exactly what is going on with these more fluffy tailed species. It has been suggested that such false heads may be aimed more at deflecting attacks by spiders rather than birds. Or it might be that lizards are mesmerized by white fluffy tails and cannot resist having a bite!
I have seen some photographs which have shown how effective false heads are on some lycaenids, when seen from behind! I have not managed to capture this myself, the best I could do was this partial rear view of Long-banded Silverline (Spindasis lohita) in another blog on this topic.
There is clearly scope for much more research on this subject, but the practicalities of comparing the effectiveness of otherwise similar butterflies, with and without false heads, is somewhat daunting. And working with predators and prey like this would be quite difficult; but no doubt more experiments could be carried out in experimental arenas.
These are not the only butterflies with tails of course (see below). There may be aerodynamic advantages of having such long, tail-like appendages? Or other functions we have not guessed at. For example, long, twisted tails in some moths – such as the luna moth (Actias luna) – may help them evade predatory bats. Not something most butterflies have to worry about, but it illustrates how morphological features may have unexpected behavioural advantages.
Hailman, J. P. (1981). A test of symmetry-deception in a chaetodontid fish. Animal Behaviour.
Lee, W. J., & Moss, C. F. (2016). Can the elongated hindwing tails of fluttering moths serve as false sonar targets to divert bat attacks?. The Journal of the Acoustical Society of America, 139(5), 2579-2588.
López-Palafox, T. G., Luis-MartÍnez, A., & Cordero, C. (2015). The movement of “false antennae” in butterflies with “false head” wing patterns. Current Zoology, 61(4), 758-764.
Quicke, D. L. (2017). Mimicry, crypsis, masquerade and other adaptive resemblances. John Wiley & Sons.
Robbins, R. K. (1980). The lycaenid false head hypothesis: historical review and quantitative analysis.
Robbins, R. K. (1981). The” false head” hypothesis: predation and wing pattern variation of lycaenid butterflies. The American Naturalist, 118(5), 770-775.
Sourakov, A. (2013). Two heads are better than one: false head allows Calycopis cecrops (Lycaenidae) to escape predation by a jumping spider, Phidippus pulcherrimus (Salticidae). Journal of natural history, 47(15-16), 1047-1054.