As the bees start to emerge in spring, it’s not unusual to find a tired out bumblebee in the garden. Bees need to warm up in the sunshine before they can fly, so keep an eye on your bee if it is in a safe place, because it might simply be recharging in the sun.
If your bumblebee is on a path or somewhere that it could be injured, or worse, then gently coax it onto a leaf and move it somewhere safe. Have a look around and see what plants are in flower. Find something that has nectar rich flowers and place the bee onto the flowers.
It’s pretty likely that you’ve found a Queen bumblebee at this time of year and if you can save her and give her an energy boost she should be able to continue on her way. By saving one bee you are potentially saving a generation or more of that species, because your queen bee will go on to make a nest and raise new queen bees and workers and males later in the season.
If you can’t find anything in flower to help your bee, then you can administer Bee Rescue Remedy. You need to make this by mixing equal parts white sugar with warm water to make a syrup. It must be cool before you feed it to your bee.
You can read a bit more about this here at Bee Rescue.