Earlier this year I received a couple of butterfly records from a survey carried out near King’s Cliffe in 2022. A Meadow Brown and a Small Tortoiseshell. However, this record really stood out because, amazingly, they were mating. Not mating with members of their own species but mating with each other! As far as I am aware this is the first-time cross-species mating in butterflies has been documented here in Northamptonshire.
The Meadow Brown does seem to have a bit of a history doing this sort of thing. In the past, I’ve noticed a few photographs of cross-species mating in butterflies appearing on social media and they very often seem to involve a Meadow Brown. The Blues seem to do it quite regularly too, especially in the south of the UK where they appear in larger numbers. Normally butterflies can attempt to alleviate these pairings by having differing anatomy in the genitalia. However, species of the same genus can have a genitalia structure that is close enough to allow pairings. In an even smaller proportion of butterflies, if they are genetically close enough, they can produce fertile hybrid young. In Europe, 16% of butterflies are known to hybridize in the wild and around half of these hybrids are fertile. The only documented true hybridization in butterflies in the UK involves the Brown Argus and Northern Brown Argus. These two very similar species can hybridize where their two populations meet. Climate change is causing a lot of butterfly species to head northwards in the UK and as this happens Brown Argus populations are meeting with Northern Brown Argus populations with increasing regularity. It is thought that eventually, if climate change continues the way it is, then the Northern Brown Argus as a species in the UK may cease to exist.
Going back to the Small Tortoiseshell and Meadow Brown pairing, while they are both members of the Nymphalidae family of butterflies they are of different genus. The Small Tortoiseshell is a member of the genus Aglais and the Meadow Brown is a member of the genus Maniola. Therefore, despite the miraculous fact that they even managed to pair at all, the result of this pairing will undoubtedly result in unviable eggs.
Many thanks to Nathalie Hueber for sending me the record. It is proof that no matter how much you study a county’s wildlife something new will always pop up!