When I first saw this pair of Wood white butterflies in Spain, I did not realise that they were mating, i.e. in copula, as they were at right angles to each other. But it soon became apparent as I took a series of photographs highlighting both the male and female. The sexes can be told apart by their antennae: the males have a patch of white scales on the underside of the club-shaped, tip of the antenna. The antennae can be seen more clearly in the following two photographs.

The lovely white scales (on antennal segments 5-11), together with the beautiful pale blue eye, are clearly visible (below).

When butterflies come together in courtship, they first have to recognise each other as being of the same species, and secondly, they need to make sure that the other individual is a butterfly they want to mate with; i.e. it is of the opposite sex! Presumably, females can quickly tell that he is a male as he waves his antennae in front of her!

The courtship behaviour of Wood Whites is a fascinating subject, and one I have written about before (Wood Whites Go A-Courting!). I hope these new photographs of courtship and mating in this species will interest and entertain readers as much as it does me! The courtship behaviour of this species was described in a seminal paper by Professor Christer Wiklund of the University of Stockholm, in 1977. There are some excellent photographs of courtship and mating in that paper, but it will not be readily accessible, for most readers. Professor Wiklund describes in wonderful detail, the courtship behaviour between males and females, and the differences which can be observed if the female has already mated.

“After alighting directly opposite to a female the male would instantaneously uncoil his proboscis until it was fully extended and pointing forward, bend both antennae downwards, and proceed to sway the head repeatedly sideways left-right, approximately 50-60 beats per min, for an indefinite period of time.” (Wiklund, 1977).

The male uses his proboscis during this courtship process, uncoiling it and extending it upwards (see below).

Although the two butterflies are very close to each other throughout this interaction, there is no actual contact and as Wiklund noted, the female bends her antennae backwards to avoid being hit by the male as he carries out his head swaying actions.

If the female is a virgin and has not yet mated, she will respond to the male’s courtship display fairly rapidly – after 10 to 90 seconds – but if she has already mated, there seems to be no clear way of conveying this to her would-be suitor, no ‘mate-refusal posture’ as seen in other pierid butterflies, and he can keep up his amorous display of head-shaking and proboscis waving for up to 35 minutes! A costly waste of time for both of them. The female pins her antennae backwards during this display. She can sometimes escape by flying upwards but she is often unable to escape his attentions. The mated female is not in a receptive state for mating again; she has already received a spermatophore from her first lover and now needs to get on and lay all the eggs she can in suitable places where they can hatch and develop.

Wood whites are said to mate, i.e. remain locked together in copula, for between 25 to 55 minutes, relatively short as far as butterfly mating goes!  I did not wait around to see how long this pair remained joined; but they were gone the following day. During the period of copulation, the male is busy forming a spermatophore inside the female, in a receptacle called the bursa copulatrix. In many species, 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, or at least until the spermatophore becomes significantly deflated. In any case, female Wood whites only mate once.

Females sometimes have to put up with the attentions of more than one male. Here is a picture of a second male trying to muscle in on a courting pair.

The male really swings his proboscis around very vigorously! There are some video recordings of this: here and here and here. Notice how the female flicks her wings in the second video (and the male then flies off!). What is actually going on when the male ‘shakes his stuff’ in this way? I can only guess, that the female is somehow able to evaluate how good a male he is; how vigorous and attractive he is, and whilst she is watching, decide whether she would like him to be the father of her eggs! That some females make their minds up in 10 seconds, whilst others seem to need a lot longer, is I think, testament to the existence of individual variation and female choice. It is in fact, evolution via sexual selection, in action! Wiklund suggests that females may communicate their willingness to mate via a pheromone, but they also signal their acceptance by making their abdomen visible between the wings (Friberg et al., 2008).

These photographs were all taken in northern Galicia (La Coruna province) in NW Spain. There are in fact three, largely identical Wood White species in Europe:  (Leptidea sinapis (Linnaeus, 1758), Leptidea reali (Reissinger, 1990) and Leptidea juvernica (Williams, 1946). I have previously assumed that I was seeing Leptidea sinapis in this region, but there are records of Leptidea reali in northern Spain (see Dincă, et al, 2011 and 2013), so now I am not so sure! There is said to be a ‘large overlap in geographical distribution and the occurrence of sympatric populations all over Europe’ (Dincă et al., 2013).

From a behavioural perspective, the key factor is that males cannot tell the different species apart and therefore court any female (where there are more than one Leptidea species in the vicinity). Females, on the other hand, are able to distinguish their own species (although they cannot tell a male from another species to stop wasting his time and find one of his own sort!). Sounds like a recipe for confusion (?), but in reality it is just evolution in action. The three very closely related species have just not separated sufficiently to be able to distinguish each other very well, but the female is able to make the choices which keep them separated.

Are there differences between the courting behaviour of these cryptic species? Here is a video of the Cryptic Wood White (Leptidea juvernica) courtship display filmed in Northern Ireland. Plenty of scope for further observations and research on these fascinating species.

References

Dincă, V., Lukhtanov, V. A., Talavera, G., & Vila, R. (2011). Unexpected layers of cryptic diversity in wood white Leptidea butterflies. Nature communications, 2, 324.

Dincă, V., Wiklund, C., Lukhtanov, V. A., Kodandaramaiah, U., Norén, K., Dapporto, L., … & Friberg, M. (2013). Reproductive isolation and patterns of genetic differentiation in a cryptic butterfly species complex. Journal of Evolutionary Biology, 26(10), 2095-2106.

Friberg, M., Vongvanich, N., Borg-Karlson, A. K., Kemp, D. J., Merilaita, S., & Wiklund, C. (2007). Female mate choice determines reproductive isolation between sympatric butterflies. Behavioral Ecology and Sociobiology, 62(6), 873-886.

Wiklund, C. (1977). Courtship behaviour in relation to female monogamy in Leptidea sinapis (Lepidoptera). Oikos 29(2), 275-283.