Risk-averse parenting: bumble bees prioritize metal avoidance over sugar intake to safeguard offspring

Metal pollution poses a growing threat to wildlife, including bees, which play a crucial role in pollination. While the toxic effects of metals on bees are well documented, their ability to avoid contaminated food sources, and whether this behaviour is shaped by social context, remains unclear. Using the buff-tailed bumble bee and two metals, copper (i.e. essential metal) and cadmium (i.e. non-essential metal), we first assessed workers' avoidance of metal-laced 50% sucrose solutions when given the choice of an uncontaminated alternative. We introduced an energetic trade-off situation by reducing sucrose concentration to 20% in the untreated solution. Finally, to test the influence of brood care, workers were kept either with or without larval siblings. When both treated and untreated solutions contained 50% sucrose, workers consistently avoided the metal-contaminated solution, regardless of brood presence. However, when sucrose concentration was reduced in the uncontaminated solution, workers preferred the contaminated option, but only in the absence of brood. In the presence of brood, workers favoured the metal-free but sucrose-poor solution, suggesting adaptive provisioning behaviour to protect larvae. This study provides the first evidence that bumble bee workers not only actively avoid metal-contaminated solutions but also adjust foraging strategies based on social context.