This parasitic fly gives birth inside of crickets

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It’s pretty rare, but just like us mammals, some flies actually give live birth. One of them is a parasitic fly species Ormia ochracea (O. ochracea). A new study published this week in the Annals of the Entomological Society of America details how female O. ochracea flies develops its young and give live birth–while feeding on its host.

“The findings also lay the groundwork for future genetic and developmental research in Ormia, a species already well-known in neuroethology for its miniature, highly directional auditory system and precise host-seeking behavior,” said Norman Lee, a study co-author and neuroscientist at St. Olaf College in Minnesota.

Mammals are not the only members of the animal kingdom that reproduce through live birth. Many shark species including porbeagles, hammerheads, makos, and great whites give birth to live pups instead of laying eggs like other fish. Some frog species have young that burst out of their backs instead of in eggs. Three lizard species are known to perform the evolutionary magic trick of laying eggs and giving live birth: Lerista bougainvillii, Zootoca vivipara, and Saiphos equalis.

To study this phenomenon in insects, a team of scientists looked at O. ochracea. These parasitic flies latch onto crickets and can use incredibly accurate directional hearing to locate singing crickets.

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Biologist and former St. Olaf College undergraduate Parker Henderson used a combination of dissection, fluorescence staining, and microscopy, to observe and document how female O. ochracea carry their developing embryos in a uterus-like structure. The embryos are completely nourished internally until they hatch as fully formed larvae. The O. ochracea larvae are then deposited directly onto a host cricket, where the flies burrow inside, and complete their development within the cricket’s body. They ultimately kill their cricket host, in somewhere between 10 to 14 days.

The study shows how the embryos grow substantially in utero. They are likely receiving nourishment from their mothers during development, which is a reproductive mode known as adenotrophic viviparity. These flies also have some capacity for partial parthenogenesis, or when an embryo develops from an unfertilized egg. In O. ochracea, unfertilized eggs from virgin females undergo the early stages of development, including nuclear division and rudimentary patterning. However, these embryos did not complete larval formation. This internal embryonic development also poses technical challenges for genetic manipulation, so any future tools to study this species’ genes may need to target sperm instead of eggs.

“This work highlights an extraordinary and underappreciated side of Ormia biology,” said study co-author and St. Olaf College biologist Eric Cole. “The complexity of their reproductive strategy raises fascinating questions about insect development and host-parasite evolution.”

*Fluorescence microscopy reveals patterns of nuclear division in a parasitic fly embryo within this insect’s extraordinary “uterus.” CREDIT: St. Olaf College.*

For scientists, understanding how parasites like O. ochracea reproduce and interact with their hosts helps explain some of the broader ecological and evolutionary dynamics at play. Understanding how these dynamics work can be relevant in agriculture and disease and pest control. Insights gained from this fly-cricket parasitic relationship could also inform more bio-inspired technologies. Ormia’s hyperaccurate directional hearing has already influenced the development of new hearing aid designs and acoustic sensor development.

Additionally, engaging undergraduates students in this kind of research strengthens scientific literacy and the public understanding of how science works. Henderson completed this project as part of his undergraduate research training, which led him to fully pursue a career in scientific research.

[ Related: Flies with shorter eye-stalks act aggressively because females are less attracted to them. ]

“This kind of hands-on work is what brings science to life. It’s how you learn to think like a scientist and contribute to new knowledge,” Henderson said in a statement.

Henderson is also a co-author on a companion paper that investigates how resource competition among larvae affects the eventual developmental outcomes in O. ochracea.

“Undergraduate research doesn’t just produce meaningful discoveries. It cultivates future scientists,” Lee concluded. “Continued investment in student research is essential to both the scientific enterprise and to building a more capable STEM workforce.”