It makes me wonder how the bees collect it. As it ends up in the corbicula (pollen basket) it must be gathered in a way similar to pollen but it is amazing the bee doesn't end up covered in it. The bee in the photo above does have a drop of resin under the base of her wing. The bee below has propolis on her wings.
All the propolis loads I have seen hang over the edge of the corbicula on the tibia and end up half way down the basitarsus.
Propolis collection is a very specialised activity for honey bees. Here are two propolis carriers greeting each other.
Propolis is not stored in the hive but is used immediately. It is only collected on warm days because it is hard and brittle at lower temperatures. I read that bees are unable to unload it themselves, as they do with pollen, but have to be unloaded by house bees although I haven't seen that happening. Propolis can be reused within the hive if it is soft and pliable but not once it has hardened.
My next task is to take a photo of a bee collecting propolis. If you have any idea how I might achieve this please leave a comment.