It has bright yellow wings and looks familiar, but this rare British butterfly is unlike any other, DNA reveals.

The British Swallowtail is the UK’s only national butterfly and the largest native butterfly. It may look similar to other swallowtails found across Europe, but its DNA tells a different story.A new study has found that the British swallowtail, also known as Papilio machaon britannicus, is a genetically distinct group found nowhere else in the world.The butterfly, known for its light yellow and black wings with blue and red markings, is found mainly on moors and wetlands in eastern England, especially the Norfolk Broads. Their survival is linked to a single plant called milky parsley.The researchers performed whole-genome re-sequencing on three British swallowtail butterflies and compared the results to existing genetic data from swallowtail populations across Europe and North Africa.They hoped to answer two big questions: whether the British swallowtail really belonged to a different lineage and whether its small habitat had led to a deleterious genetic decline over time.The results, published in the journal Insect Conservation and Diversity, revealed that the British swallowtail is genetically distinct.

The study found that its genetic diversity is about 20% less than its European relatives.However, despite its limited range and low genetic diversity, the researchers found that the butterfly did not accumulate a large number of harmful mutations.At the same time, the study found much higher levels of inbreeding in British populations compared to swallowtail populations in mainland Europe. This may create challenges to the butterfly’s long-term survival, the researchers said.The question of whether the British swallowtail is truly distinct has been debated for years. Although the butterfly is classified as vulnerable and legally protected in the United Kingdom, its taxonomic status has remained uncertain.The researchers note that this is not unusual. The genetic diversity of many insect species remains poorly understood because genetic studies often focus on identifying hidden species rather than measuring the genetic health of populations.In recent years, genetic research has helped scientists better understand swallowtail butterflies around the Mediterranean region. Previous studies have confirmed that the North African swallowtail, Papilio saharae, is a separate species although it closely resembles the European swallowtail.Previous genetic studies of the British swallowtail have shown mixed results. According to the researchers, clear genomic evidence is important because it helps conservation planners decide how best to protect small, isolated populations.For the new study, scientists collected DNA from three British swallowtails on the Norfolk Broads. They removed a small portion of one of the front legs of each living butterfly and then released the insects back into the wild. The team also collected DNA samples from swallowtails in Sweden and Russia for comparison.Instead of examining a small number of genetic markers, the researchers used whole-genome sequencing, which helped them study the complete genetic blueprint.The team then measured the amount of genetic variation in each group, checking for evidence of inbreeding and examining whether deleterious mutations accumulate over time.The results showed that the British swallowtail population is genetically distinct and isolated. Researchers estimate that their population size is about 8.8 times smaller than those on the European mainland. They also found that British butterflies possess roughly a fifth of the genetic diversity found in their continental relatives.One of the clearest signs of inbreeding was the presence of longer “homozygous chains.” These are long stretches of DNA where the genetic material inherited from both parents is identical, mostly because the parents share a common ancestor.The researchers also used demographic modeling, a method that helps scientists study population history. While the analysis does not clearly show recent changes in population size, it does suggest that there may have been limited gene flow between British and mainland European swallowtails in the past.The researchers said the study helps settle a long-standing debate about the genetic uniqueness of the British swallowtail. They added that genomics research could become an important tool for butterfly conservation efforts, especially as climate change, habitat loss and intensive agriculture continue to put pressure on vulnerable butterfly populations.