It is not unusual to come across mating butterflies, although sometimes copulation takes place well away from where they normally feed or defend territories: for example, in the tree tops or deep in the undergrowth. Mating is risky; copulating pairs are usually relatively inactive and therefore vulnerable to attack by predators. The scientific term for when they are locked together like this is in copula.
Butterflies remain in copula for very variable amounts of time, from the brief (20 minutes) to the lengthy (27 hours) (Shields and Emmel, 1973). The mating pairs may be stationary and cryptic, or relatively mobile, flying about whilst locked together as here with a pair of Gatekeeper butterflies (Pyronia tithonus). One individual, usually the largest sex – the female – in a dimorphic species like this, does the carrying. In species where the two sexes are about the same size, the individual flying about and carrying the other one can be of either sex, although one sex usually predominates in this role. 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, as shown here (below).
What are they doing whilst they are locked together like this? The male is making and transferring a spermatophore. Male butterflies usually make a significant contribution to the reproductive process in the form of a large spermataphore, which has been called, somewhat prosaically, a ‘nuptial gift’. The size of the male contribution is sometimes so large it is commensurate with that of the female’s investment – in terms of eggs – in some species. Spermatophores can represent over 20% of a male butterfly’s body weight, but the mass is significantly reduced when a male comes to mate a second time.
The ejaculate transferred to the female during mating contains sperm, nutrients, anti-aphrodisaics and hormones (Wickland et al., 2001). Most of the sperm are so-called, apyrene sperm – without a nucleus – and play no role in fertilisation. A smaller proportion, 10-15%, are genuine (eupyrene) sperm which are capable of fertilising eggs. The smaller anuceate sperm are in effect a protein contribution from the male to the female: his parental investment in the reproduction process; a sort of protein meal for her if you will. The so-called, ‘anti-aphrodisiacs’ are chemicals which in effect makes the female appear unreceptive and unattractive to other would-be suitors! (Andersson et al., 2000).
Spermatophores are composed of a tough, indigestible outer envelope, an inner matrix, and a bolus of sperm. The spermatophore itself is formed inside the female in a receptacle called the bursa copulatrix, during mating. Remarkably, the physical effect of the spermatophore in stretching the bursa of the female changes her behaviour, such that she is no longer receptive to other males, at least for a while (Meslin et al., 2017)!
These photographs were taken on 14th Aug 2017 in Galicia, Spain.
Andersson, J. et al. (2000). Sexual cooperation and conflict in butterflies: a male-transferred anti-aphrodisiac reduces harassment of recently mated females. Proc. R. Soc. Lond. B (2000) 267, 1271-1275.
Meslin, C., Tamara S. Cherwin, Melissa S. Plakke, Brandon S. Small, Breanna J. Goetz, Nathan I. Morehouse, and Nathan L. Clark (2017). Structural complexity and molecular heterogeneity of a butterfly ejaculate reflect a complex history of selection. PNAS 114 (27) E5406-E5413.
Shields and Emmel, J. F. (1973). A review of carrying pair and mating times in butterflies. J. Res. Lepid. 12: 25-64.
Wiklund, C., Karlsson, B. and Leimar, O. (2001). Sexual conflict and cooperation in butterfly reproduction: a comparative study of polyandry and female fitness. Proc. R. Soc. Lond. (B) 268: 1661-667.