Dandelions are one of the last flowers standing in the fall. Spray one with roundup and you're spraying every bumblebee queen that visits, just as she's preparing to hibernate. The flower doesn't die on contact. It takes days, and it keeps getting visited the entire time. Bumblebee queens are feeding hard right now, building the fat reserves that have to carry them through months underground with no colony and no food. Every queen that doesn't fatten up is a colony that doesn't start next spring. Research from Finland found glyphosate-exposed bumblebees lost the ability to tell flowers apart by color, and lost their sensitivity to the ultraviolet patterns bees use to find nectar. Late solitary bees, hoverflies, and butterflies are working the same flowers too. If the dandelions genuinely bother you, dig them out. A weeding fork gets the taproot. Or leave them. The first hard frost takes care of it.