Patterns of Estimated Prevalence of Bot Fly Larvae in Harvested Squirrels in Pennsylvania

Joshua B. Johnson^1,*, Emily S. Boyd¹, Melanie Weaver¹, and Justin D. Brown²

¹Pennsylvania Game Commission, 2001 Elmerton Avenue, Harrisburg, PA 17110. ²Department of Veterinary and Biomedical Sciences, 115 Henning Building, Pennsylvania State University, University Park, PA 16802. *Corresponding author.

Northeastern Naturalist, Volume 31, Issue 1 (2024): 110–119

First published early online: 26 March 2024

Abstract
From 2020 to 2023, we used diaries from squirrel hunters to estimate the prevalence of Cuterebra emasculator (Squirrel Bot Fly), which parasitize and burrow under the skin of chipmunks and tree squirrels and form bulges called “warbles”, among 3 tree squirrel species in Pennsylvania. We received diaries from 1222 squirrel hunters who harvested 7356 squirrels, of which 249 (3.4%) were reported to have subcutaneous swellings consistent with warbles. Annual prevalence rates varied from 2.5% to 3.9%, were consistently highest during the first week of the hunting season (mid-September), and declined to near zero by December. Overall, warbles were more prevalent in Sciurus carolinensis (Eastern Gray Squirrel; 3.6%) than in S. niger (Eastern Fox Squirrel; 1.3%) and Tamiasciurus hudsonicus (American Red Squirrel; 0.0%). During the first 5 weeks of the squirrel-hunting season, squirrels harvested in southern latitudes had higher warble prevalence rates (6.4%) than in northern latitudes (4.1%), but no associations were observed between prevalence and physiographic province. Providing earlier hunting-season opportunities increased the likelihood that hunters would encounter squirrels with warbles than they did historically. Communications efforts should focus on educating hunters on the occurrence of warbles in squirrels in Pennsylvania, particularly during the early season, and on the lack of public health impacts of this disease on squirrel meat.

Download Full-text pdf (Accessible only to subscribers. To subscribe click here.)