Bombus sylvarum

Bombus sylvarum (Linnaeus, 1761) Conservation status CR Distribution Bombus sylvarum has a large distribution in the West Palearctic (Rasmont et al. 2021). In Belgium, the species was extirpated from many localities where it used to thrive, especially in the western part of its distribution. Most of its subsisting locations are now concentrated east of the Sambre and Meuse valley. It can be noted that, even historically, B. sylvarum never seemed abundant in the country (Folschweiller 2020). Although habitat degradation has likely led the Belgian populations to their current status, climate change is expected to further impact the European range of B. sylvarum by the end of the century (Rasmont et al. 2015, Ghisbain et al. 2024). Notes Bombus sylvarum lives in a range of more or less open, flower-rich habitats where it can collect pollen from plants of the Fabaceae and Lamiaceae families (Rasmont et al. 2021, Wood et al. 2021). Notably, of the five individuals collected, only one was foraging on a plant from the Fabaceae family. Two were foraging on Asteraceae, one on Onagraceae, and one on Plantaginaceae. Folschweiller 2020 cite the species as frequently in sympatry with B. humilis and B. veteranus, two strongly-threatened species at the Belgian scale. Diagnosis In Belgium, the females of Bombus sylvarum (Fig. 9) can only be confused with those of B. veteranus. In the latter, the basis of the tergites 3 to 5 always include black hairs, which is not the case in the females of B. sylvarum. Furthermore, the mandibles of B. veteranus are substantially elongated, while those of B. sylvarum have a regular size, comparable to those of other females of free-living bumblebees. The males of B. sylvarum can be differentiated from the males of all other bumblebee species on the basis of the morphology of their genitalia (drawn in Rasmont et al. 2021).