14 January 2012

Butterfly Courtship Rituals

Butterfly Courtship Rituals
Success strategies in finding the right mate

A large part of a butterfly's lifespan is spent directly or indirectly to achieve a particular objective - that of procreation. A newly eclosed butterfly spends most of its day feeding to build up its reserves and energy so that it can survive and search for a mate and to quickly ensure the continued survival of the species before it dies or succumbs to predation.

For a butterfly to be able to fulfil its objective of mating and producing viable eggs for the next generation, the males and females have to first locate each other. Males have to correctly identify a female of his own species by visual cues. A variety of characteristics, from colour, pattern, size, flight and other behavioural attributes that may not be apparent to the human eye, are used to assess the butterflies that they encounter.

Locating a Mate
So where does a fertile male go to look for potential females to mate with? Males generally have two main strategies. The first is perching or hill-topping. Basically, this method requires the male to search out a high vantage point from which he can have a clear view of an area. The moment an intruder or any movement is detected, the male will dart down and check out the newcomer into his territory.

If the intruder is a male, or a butterfly of another species, the male dives into the path of the newcomer and "attacks" it. An aerial dogfight ensues, until the intruder leaves the incumbent's territory. The resident male then returns to one of several favourite perches, and then continues to monitor his domain for new activity.

Hilltops or tall trees with the surrounding vegetation lower are ideal places for the 'perching' strategy. Hence such places function as a "singles' club" for both males and females of a species to find each other.

The second strategy employed by males of butterflies is what is referred to as "patrolling". The male flies continuously along tracks, forest edges and streams to look out for females. As it detects females by visual contact, it will check out anything that is in motion and even if it vaguely resembles a female of its own species.

Some males also patrol near its caterpillar host plants, with the objective of finding a newly-eclosed female of the same species. A well-known phenomenon amongst the Heliconiinae of South America is "pupal rape" where males of a particular species tear through the pupal shell of a female of the same species to mate with her even before she ecloses!

When a male locates a female of his own species, it will switch to courtship mode and track the female persistently. He then begins the rituals of courtship. For the male, finding the prospective mate is just the beginning. There are still no guarantees that the female will considering him worthy of fertilising her offspring.

The female being courted will assess and choose the male depending on age, general appearance and health and potential ability to provide viable spermatophore for her reproductive success. Females of many species tend to mate only once so her choice is crucial. Indeed, many ButterflyCircle members have observed an ovipositing female, collected the eggs for breeding, only to find that the eggs were infertile and did not hatch at all! Could that be due to her eggs not being successfully fertilised by the male?

Courtship for the male commences with trying to get the female's attention, via a series of signals, ranging from flapping around the female to gain her attention (she may be going around her own business of feeding for example), sending chemical signals to her, in the form of pheromones. A typical movement is where the male flaps in position, usually upwind from the female, and release his pheromones so that she gets a clear signal of his intention to mate.

In the male, pheromones are usually found in the specialised scales on various parts of the wing - called androconial cells, specialised organs like the hair pencils in Danaianae species, or hair brushes on the undersides of the wings brushing against a special scent organs on the wings.

The female which picks up the signals then decides on her next course of action. She may continue with her own business and fly away, totally ignore the male. Of course, the male usually being persistent in his courtship attempts (like some men do in our human world!), will take the initial rejection in his stride and continue to re-send the physical and chemical signals to the female repeatedly.

Once again, the female may fly off, indicating that she is not interested. This can go on for several attempts before the female responds, or continues to reject the male until he gets the message and gives up.

In some cases, the males are more aggressive and flies in such a way as to obstruct the female's ability to fly off, or corners her. If the female is still not interested, she will usually stop with her wings opened, and adopt her "rejection posture".

This is usually done with her wings opened either fully flat or half-opened, but with her abdomen thrust upwards and elevated such that it would be all but impossible for the male to clasp the end of her abdomen. A persistent male may still flap violently above the female and try to push her abdomen down, but he will usually fail, and fly off after a few attempts.

If the female responds positively and decides to accept her suitor's advances, she will close her wings and remain still. This signals the male to now approach her. He will land beside her, flick his wings a few times, moves beside her facing the same direction, and curls his abdomen towards hers and grasps hers using his claspers. The receptive female will extend and offer her abdomen for coupling.

Once engaged, the coupled butterflies will face away from each other in the usual mating pose. Usually, if disturbed, the larger wingspan of the two (usually the female) will do the flying, whilst the other partner remains still. It would be unimaginable for both to fly at the same time, and in opposite directions!

In the field, we have seen impatient male butterflies hovering around pupae from which females are about to eclose, and immediately mate with them when the female breaks out of her pupa. Copulation occurs even before the female is able to dry her wings properly. In one case, the male was so insistent on 'doing it' that he damaged the wings of the female, leaving her crippled and unable to fly!

In other cases, we have also observed males of various species coupling in flight in an instant, dispensing with the long courtship rituals and avoid suffering the fate of rejection. One example that I have personally witnessed, was when a male, perched on a high vantage position, swooped down on a passing female, engaged her in mid-air, and both fell downwards, coupled into the bushes and stayed mated for quite some time! Now that, I would call precision engagement!

And so we see how in the world of butterflies, males have to woo their mates and work hard before they can successfully mate with a female of their choice. Males will often have to suffer the 'indignity' of rejection as there are no guarantees that the female that they have targeted, would accept them, no matter how hard they try. But like all things in life, success always comes to those who are persistent in the face of failure and work hard for it.

Text by Khew SK : Photos by Sunny Chir, Federick Ho, Khew SK,Terry Ong & Anthony Wong

References :
  • Handbook for Butterfly Watchers : Robert M Pyle, 1984, 1992; Houghton Mifflin Company, New York
  • A World for Butterflies - Their Lives, Behavior and Future : Dr Phil Schappert, 2000; Firefly Books
  • Butterflies : Dick Vane-Wright, 2003; The Natural History Museum, London


Friend of HK said...

Very interesting information and superb pictures!

Commander said...

Thanks for your kind comments, Friend of HK.

Andrea said...

A very well written article, and very informative. I just wonder how the observers were able to know the time the pheromones are dispensed.

Commander said...

Thanks, Andrea. There are a number of scientific papers that are well researched and have presented the methodology on how pheremones work in Lepidoptera (both moths and butterflies). The subject is highly technical and probably beyond most laymen hobbyists (me included!) , and I've tried to distil the articles that I've referred to, and present the information in a more reader-friendly manner. If any of our readers could help enlighten us, it would be most welcomed so that we can all learn better. Cheers.

Carol said...

Fabulous blog! What fascinating butterflies you capture so beautifully! Thanks to Andrea for introducing me to your world of butterflies.

Commander said...

Thanks for your kind comments, Carol. Do come and visit often, as we have weekly articles (sometimes more) that feature the world and beauty of butterflies. :)

Nick Morgan said...

Fantastic photographs of stunning butterflies. Just came across your web site and I will now be returning regularly. So much information on here. Well done!

Commander said...

Thanks for your kind words, Nick! Do come back for more! :)

Unknown said...

Wonder whether the female butts have their territory and fight for it?

Ray Cannon said...

I would be most interested to know the species which 'swooped down on a passing female, engaged her in mid-air'. These are valuable observations and it would be useful to be able to record and quote them. Many thanks,
Ray Cannon