Rain chills the flight muscles that bees need to fly, so while they can fly in the rain for a limited amount of time, they tend to avoid it. Bees will stay in their hives if barometric pressure indicates rain is on the way.
Bees are able to sense when a rain storm is coming due to pressure in the atmosphere. Some bees may fly back to their hives when a rain starts, but most bees will not leave their hives when it is raining. If the rain is too heavy, they are unable to fly. Some scientists also believe that since bees use the sun to navigate, they are unable to when it is raining due to the clouds.
Part of the natural instinct for bees to avoid the rain is because they are not fast at flying like other insects. Instead, their flight speed average is about 15 miles per hour, compared to 36 miles per hour like some dragonflies.