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Over the past few weeks, I’ve been watching Orange Tips flitting up and down the lane near our home on the edge of Exmoor. One thing I noticed is that the males, marked by their distinctive orange-tipped wings, tend to emerge up to a week or more before the females. The females, lacking this vibrant coloration (Figs. 1a & b), still share with the males a beautiful green filigree pattern on the underside of the lower wings. This likely serves as cryptic camouflage while they nectar on flowers or, in the case of females, lay eggs on host plants such as garlic mustard.

It’s commonly assumed that the sexual dimorphism seen in Orange Tips exists primarily for intraspecific recognition—helping males and females of the same species find each other. But watching them, I wondered whether the orange tips might also play a role in interspecific recognition. Several other similarly sized white butterflies from the Pieridae family—such as the Large, Small, and Green-veined Whites—are active at this same time of year (April-May-June).

I’ve often observed male white butterflies fly up to other whites, leading to brief aerial pursuits. These encounters sometimes escalate into a spiralling aerial dance before the butterflies part ways—having presumably recognized that the other is either a male or a non-receptive female (perhaps one that has already mated and laid eggs). In this competitive mating environment, it seems plausible that male Orange Tips benefit from making themselves easily distinguishable. Their vivid orange markings could reduce both intra- and interspecific harassment by signalling clearly that they are not potential mates to other males, particularly from other Pierid species.

Interestingly, within their own species, male Large, Small, and Green-veined Whites appear to distinguish males from females with impressive speed and accuracy. This may be due to subtle but reliable visual cues: males have one black spot on the upper forewing (or none, in the case of the Large White), while females have two. This suggests that these butterflies possess not only excellent visual acuity but possibly even the capacity to “count”—at least up to two!

While visual signals clearly play a significant role, chemical cues likely do as well. Pheromones are known to be involved in shorter-range courtship in butterflies (Cannon, 2020; Nobre et al., 2021), and may assist in determining mate receptivity. However, this remains speculative in many cases.

Adding further nuance, some butterfly species—like the Peacock, Small Tortoiseshell, and Comma (Family Nymphalidae)—show little to no sexual dimorphism in wing coloration, yet males still manage to locate receptive females. Conversely, other Nymphalids, such as the Silver-washed Fritillary, do exhibit dimorphism: males have dark androconial bars across their upper forewings, which release sex pheromones during courtship (Cannon, 2020). In the polymorphic female form, valezina, the females appear bronze-green, in contrast to the typical red-brown coloration of both sexes in the usual form (Riley, 2007).

In the Skipper family (Hesperiidae), the sexes are usually similar, though females are slightly larger, and in some species, such as the Large Skipper, males display a single dark androconial bar on each forewing.

Among the British Pierids, sexual dimorphism varies. Brimstones show it quite clearly, whereas Clouded Yellows differ more subtly—females have yellow spots along the black wing borders. Brown butterflies (Family Satyridae), like the Gatekeeper, show male-specific features such as curved androconial bars. The Blue butterflies (Family Lycaenidae) also tend to exhibit sexual dimorphism, with males typically blue and females blue-brown or brown. But exceptions exist: in the Brown Argus, both sexes are similarly brown. Copper butterflies and hairstreaks, also Lycaenids, vary by species. Interestingly, the British Swallowtail (Family Papilionidae) does not show notable sexual dimorphism, while the Duke of Burgundy (Family Riodinidae) does (Riley, 2007).

All this points to a simple but profound truth: nature resists generalization. The evolution of sexual dimorphism in butterflies is shaped by a complex mix of ecological pressures, mating systems, and evolutionary histories. What works for one species—or even one population—may not for another. In the ongoing and intricate dance of butterfly courtship, we likely understand far less than we like to admit. Clearly, there’s ample room for further research, particularly through detailed observational studies.

References:

Cannon, R.J.C. (2020). Courtship and Mating in Butterflies. CABI, Wallingford, Oxfordshire, UK. Pp. 375.

Nobre, C. E. B., Lucas, L. A. D. S., Padilha, R. J. R., Navarro, D. M. D. A. F., Alves, L. C., & Maia, A. C. D. (2021). Specialized androconial scales conceal species-specific semiochemicals of sympatric sulphur butterflies (Lepidoptera: Pieridae: Coliadinae). Organisms Diversity & Evolution 21, 93-105.

Riley, A.M. (2007). British and Irish Butterflies: The Complete Identification, Field and Site Guide to the Species, Subspecies and Forms. Brambleby Books: Luton, UK. p. 352.

     

Figs. 1a & b. Orange Tip butterfly, Anthocharis cardemines; (a, left) male, (b, right) female