Essentially, all animals face parasites, but little data are available on the rate of parasitism in wild animals, particularly in insects. Here, we report observations of more than 400 bumblebee workers collected at an Alpine site, including the parasites observed (Crithidia bombi, Nosema bombi, conopid parasitoid fly larvae and tracheal mites), as well as date of collection, bumblebee species and body variables (size, fat content, egg development and antibacterial activity). Among the 14 bumblebee species collected, C. bombi and tracheal mites reached a prevalence of approximately 10 and 6%, respectively, while conopids and N. bombi were almost absent. Correlations among the measured parameters suggest that larger workers are more likely to develop eggs and contain more tracheal mites. Across the season, we found a decrease in fat content but an increase in C. bombi and mite prevalence. Mites’ fitness was higher in fatter bees and lower in bees with more tracheal mites. Antibacterial activity was found in approximately 10% of the workers, suggesting at least sporadic infection with bacteria.