Bumble bee success in diverse thermal environments, from the tropics to the poles and from sea level to the highest mountaintops, depends in part on their heterothermic lifestyle. They endogenously regulate high temperatures for flight, foraging, and incubation, but can also shut down to save energy via ectothermy. Maintaining cellular function at different temperatures often requires membrane remodeling, such that fluidity and the myriad cellular processes that depend on it stays in an optimal range. Shifts in fatty acid (FA) composition are often a primary mechanism for maintaining membrane fluidity in changing temperatures, with shifts from saturated to unsaturated FA as organisms move from hot to cold, respectively. This homeoviscous adaptation may, however, be constrained by diet. To address the link between diet and lipid composition in bumble bees, we used two complementary approaches. First, we compared FA composition of flight muscle of bees reared in the lab (Bombus impatiens) with FA composition of their pollen diet (both determined by GC-FID). Second, we compared FA composition of wild-caught worker bees (B. huntii and B. griseocollis) with FA composition of their pollen baskets. Both lab-reared and wild-caught bees were enriched in longer chain, unsaturated FA relative to their pollen diet, likely reflective of enzymatic pathways described in other insects (elongases, desaturases). Despite carrying pollen with similar FA composition, wild species differed in FA composition. Combining diet experiments with thermal challenges will help us better elucidate the influence of diet on membrane remodeling in response to temperature fluctuations these widespread pollinators must often face.