Imagine a fly that decides flying is overrated. Instead, it finds a bat, sheds its wings, drops its legs, and burrows into the host’s skin for the rest of its days. This is the reality of the genus Ascodipteron, a group of highly specialised bat flies that challenge our basic definition of what an insect looks like.
In a recent study published in the open-access journal ZooKeys, researchers led by Haoran Sun of Beijing Forestry University have identified a new member of this strange family in the Yunnan Province of China. It brings some fascinating, if slightly macabre, biological quirks to the table.
The newly discovered species has been named Ascodipteron euryale and was found on the lesser brown horseshoe bat, known scientifically as Rhinolophus stheno. This discovery is particularly significant because it represents the first time a fly from this genus has been documented on this specific species of bat. These flies often show an incredibly narrow host range and a strict preference for where they live on the bat’s body. In the case of Ascodipteron euryale, they prefer the base of the bat’s ear, the tragus, or the ear pinna.
The life of a female Ascodipteron fly is especially interesting. After a very brief period of seeking out a host, the female undergoes a radical transformation into what scientists call a neosome. It essentially becomes an endoparasite, embedded so deeply in the bat’s tissue that often only its posterior end is visible, protruding slightly so it can breathe and release larvae. This particular species was discovered in Xianren Cave, located in the Simao District of Pu’er City, at an elevation of 2428 meters above sea level.
What makes Ascodipteron euryale stand out from its 17 known cousins? The most defining physical trait is the shape of its mesosternum, a part of its underside, which features gently rounded lobes on the back corners. Further, unlike many related flies that are covered in soft skin and easily removed, these neosomes were found encased in a fibrous cyst or shell – this is a reaction from the host bat’s own immune system, creating a protective barrier that makes the parasite very difficult to extract.
The naming of the species is a clever nod to Greek mythology. The host bat, Rhinolophus stheno, shares a name with Stheno, one of the three Gorgon sisters who could turn onlookers to stone. The researchers decided to name the new fly euryale after Euryale, another of the Gorgon sisters. In the myths, these two sisters were immortal, and the authors note that this name choice reflects their hope that the deep-rooted biological association between this specific bat and its resident fly continues long into the future.
This research adds a sixth species of Ascodipteron to the records in China, emphasising the impressive biodiversity hidden within the country’s cave systems. It also raises new questions for future study, particularly regarding why some of these flies trigger the formation of fibrous shells while others do not. For now, Ascodipteron euryale remains a testament to the strange and highly specific ways life finds a niche (even if that niche is the inside of a bat’s ear)!
Original source:
Sun H, Ding L, Zhang D, Pape T (2026) Ascodipteron (Diptera, Nycteribiidae, streblid grade) from China: a new species from the lesser brown horseshoe bat, Rhinolophus stheno. ZooKeys 1273: 277-286. https://doi.org/10.3897/zookeys.1273.183551
