Females butterflies are usually a lot more choosy than males. They produce eggs, and have more resources invested in each one; compared to the millions of tiny sperms that males can produce and put about! So for females, some of whom will only mate once, it is imperative to choose the best male, in terms of providing for her and her offspring.
In some species, females effectively control mating. For example, they do not increase the rate at which they mate when males become more persistent! It seems they cannot be hurried into making their choice. There are some species, such as the Monarch butterfly, where males can, in certain circumstances, force themselves upon the female; but for most butterfly species, females are in control of who they mate with.
The male has to court the female and gain her acceptance via attraction and persuasion! Using his looks – flashy wing colours for example – or courtship dances and seductive scents (pheromones). The female may reject many suitors before she finds a male who is good for her! Rejection and persistence is part and parcel of a male butterfly’s life! Sometimes they get so carried away (with hormones!) that they attempt to mate with a different species, as shown below, with the small white butterfly bending his abdomen towards a much larger female of another species! He had just chased her through the forest!
In many species, females may repeatedly resist male attempts to copulate – flying off when the male curls his abdomen towards them – before finally accepting his advances, perhaps after three or more tries, eventually allowing him to mate. Presumably she is evaluating his quality as a potential mate during this process. Graylings have a particularly elaborate courtship, with a repertoire of moves and motions, including the famous ‘bowing’ behaviour (below), where the male tries to take hold of the female fore-wings and antennae, letting them slide between his fore-wings, so she can ‘taste’ his pheromones!
A female who has already mated and wants to put a stop to further attentions or harassment by males has a number of options. In some butterflies, like the pierids, there are stereotypical behaviours – such as the mate refusal posture – which curtail courtship attempts by males. She raises up her abdomen, almost to a vertical position (below), often with the genitalia extruded; the message is NO, go away!
In Wood whites (below), the courting process can go on for a long time because the female – if she has already mated, for example – has no clear way of conveying this to her would-be suitor, no ‘mate-refusal posture’ she can use.
Being chased to harassed by males carries a certain risk in itself. I followed this pair of courting Marsh Fritillaries (Eurodryas aurina) for quite some time; eventually, the female flew off – chased by the male – but they both became ensnared in a spider’s web (below). In this case, I freed them from the spider’s web, but it made me think about how often such accidents happen in nature?
Copulation itself may last a long time, but it varies enormously from species to species. Some matings are relatively brief, ca. 20 minutes, others last a whole day or more! Very lengthy copulations may be a way in which males can prevent the female from mating with other males. He acts as a sort of living mating plug! But the male needs a certain about of time to form the spermatophore, which occurs inside the female.
Remaining locked together in copula potentially exposes butterflies to an increased risk of being attacked and eaten by a predator. Mating pairs may hide away deep in the foliage, but they are often relatively mobile, flying about whilst locked together in what is called the a nuptial flight. They fly slowly and laboriously when one of them has to carry the other.
One individual, usually the largest sex in those species where there is a pronounced gender size difference, does the carrying. In species of about the same size, like the Plain Tiger (Danaus chryssipus) (below), the individual flying and carrying the other can be of either sex (in this case it is the male). There are however, reports of the role of carrier alternating between the male and female during a single copulation.
The reason for the movement whilst in copula may be to allow the individual who is doing the carrying to feed, or even to bask in the sunshine, like this pair of mating Gatekeepers (below).
Once mating commences, it is usually the male who decides when to terminate copulation, when he has finished forming and transferring a spermatophore and accessory gland secretions. If the male dies whilst in copula, the female is reportedly unable to rid herself of him. What a terrible thought!
The author is writing a book on Courtship and mating in Butterflies.