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Bot Fly Larvae Found in 30 Percent of Sampled French Roe Deer

Close-up of an adult roe deer bot fly, Cephenemyia stimulator
Research · Disease, parasites & microbiology

A direct examination of 40 european roe deer (Capreolus capreolus) carcasses collected in France found larvae of the roe deer bot fly Cephenemyia stimulator in 12 animals, giving a prevalence of 30 percent in the sampled carcasses. The study examined whether fresh carcasses gathered through existing wildlife networks can provide useful epidemiological information on a parasite that is difficult to monitor in free-ranging hosts.

C. stimulator is a specialised parasite of roe deer. Its larvae develop in the nasal passages and pharynx before leaving the host to pupate. Because the larvae are hidden inside the head, direct examination of carcasses provides information that ordinary field observations cannot reveal.

Technical staff from the Fédération Nationale des Chasseurs collected the 40 carcasses between 2014 and 2016. The heads were removed, frozen and later examined by necropsy. Among the 12 infested deer, the mean intensity was 9.92 larvae, although burdens varied substantially between animals.

The 30 percent prevalence therefore describes this sample of 40 French roe deer rather than a national estimate. The authors present the work primarily as a practical demonstration of how routinely collected wildlife carcasses can be used to record both parasite occurrence and intensity and to build comparable surveillance data over time.

Sources and image credit

  1. Saez-Ventura, Á., Carrasco, A. L., Aleix-Mata, G., Sánchez, A., Faure, E., López-Montoya, A. J., & Pérez, J. M. (2026). Gathering epidemiological information from wildlife fresh carcasses: A case study of Cephenemyia stimulator (Clark, 1815) (Diptera: Oestridae) infestations in French roe deer. Annales de la Société entomologique de France (N.S.), 62(1), 77–83. https://doi.org/10.1080/00379271.2026.2621369

Image: Frank Vassen / Wikimedia Commons — adult roe deer bot fly (Cephenemyia stimulator) on Mont Lozère, France, 17 July 2019; illustrative photograph, not a specimen from the study. · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

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