The endangered swallowtail butterfly Papilio machaon britannicus, which now only regularly breeds in Britain on the Norfolk Broads, has been a distinct subspecies for at least 200,000 years, according to a new genetic study. That's considerably longer than the 8,000 years previously assumed, which is awkward for anyone who called it a 'recent upstart.'

Smaller, darker, and much rarer than its continental cousin, britannicus was thought to have developed its distinctive form after the flooding of Doggerland trapped it in eastern English wetlands. But the new whole-genome sequencing, published in Insect Conservation and Diversity, suggests it split from continental populations between 200,000 and 1.7 million years ago. It's not just a local; it's a European wetland specialist that once ranged widely across northern Europe.

The study found some inbreeding in britannicus but no damaging mutations, which is more than can be said for some royal families. The findings are likely to transform conservation approaches, especially since some butterfly experts have argued for introducing the more common continental swallowtail (Papilio machaon gorganus) into Britain, potentially hybridising britannicus out of existence. But Mark Collins, president of the Swallowtail and Birdwing Butterfly Trust and co-author of the paper, argues the genetic distinctiveness makes britannicus worthy of renewed effort.

'We're looking at a relict population in the Norfolk Broads that's not just a relict for Britain but a relict from a once much wider distribution in wetlands across Europe,' Collins said. 'Britannicus is part of our own natural heritage, it's protected by law for good reason because it's a unique thing, and we should not allow it to be wiped out.'

In the wild, britannicus caterpillars will only reliably eat milk parsley, a rare wetland plant also threatened by rising sea levels causing salination of the Norfolk Broads. With most breeding populations at or below sea level, the butterfly will need to be translocated to new wetland sites. Meanwhile, global heating is helping the continental swallowtail reach Britain more often, already breeding in Kent and Sussex during fine summers. Collins remains optimistic: 'There's every chance that the specialist wetland subspecies could survive into the future with the general swallowtail species flying around the wider countryside. Hybridisation may occur on the fringes but britannicus could endure if we preserve our wetlands.'

Nominations are now open for the Guardian's 2026 invertebrate of the year competition. This spineless wonder might not win, but at least it's been genetically verified as unique.