Two Heads Are Better Than One
by Torben B. Larsen

When wandering in forests or garden suburbs in Bangladesh you may come across one of several of the so-called false-head butterflies, like the Fluffy Tit below. Take a good look at the photograph – where would you attack if you were a predator wanting to eat it?

Predators know from experience that an attack on the head end of the butterfly is the best policy for a quick and clean kill. But where is the head? Well, the real head is the small one facing right just above the legs, but it looks less like a head than  the tails and markings facing left on the hindwing. So predators, who usually need to make a quick decision on what to do, attack the false-head. A praying mantis or a small lizard might well end up with just a bit of fluff, while hunting-spiders and other predators will not do even that, simply glancing off because they cannot get a grip.

There is – literally – another twist to the story; most false-head butterflies twist 180 degrees in the air just before landing, so that the false-head points in the flight direction. So in addition to confusing the heads, the predator also expects that the butterfly will fly off in the opposite direction. The same principle is actually seen in some fishes; here the main effect probably lies in making the larger predatory fish believe that their prey will try to escape the wrong way.

We have experimental evidence that the false-heads work as described here, and in nature it is quite common to find butterflies where the false-head is missing, symmetrically removed by a predator. Each such case might reflect several attacks where no visible damage was done, so the survival value must be great.

However, nothing comes for free. Life is full of compromises. So for a false-head to work, the butterfly must be somewhat conspicuous and might therefore be attacked more frequently than a well camouflaged relative. But that price is evidently worth paying.

So false-head butterflies must see it somewhat like this: ‘Two heads good!’ Their predators might see it rather differently: ‘Two-faced butterflies bad!’