Newly emerged bees are smaller than older bees. This has been observed since Huber's time at least. Huber thought there were two different sized bees based on their job. He didn't realize that their jobs changed by age.
"Two kinds of workers in the hive
"The following observations may also furnish indications of the presence of honey in the flowers. They are based upon a remarkable fact which was unknown to my precursors; it is that there are two kinds of workers in the hive; the ones which may attain a considerable size when they have filled themselves with all the honey that their stomach may contain, are in general destined to the elaboration of wax; the others whose abdomen does not perceptibly change in appearance, retain only the quantity of honey which is necessary for their sustenance and immediately hand out to others that which they have harvested; they are not in charge of the provisioning of the hive, their particular function being to care for the young: we will call them nurse bees, or small bees, in opposition to those whose abdomen may be dilated and which deserve the name of wax-workers.
"Although the external difference by which the two sorts may be recognized be inconsiderable, this distinction is not imaginary. Anatomical observations have taught us that there is a real difference in the capacity of their stomach. We have also ascertained that the bees of one sort cannot fulfill all the functions shared among the workers of a hive. In one of these tests we painted with different colors the bees of each class, to observe their behavior, and we did not see any interchange. In another test, we gave the bees of a queen-less colony both brood and pollen and we at once saw the small bees busy themselves with the food of the larvae, while those of the wax-working class paid no attention to them."-- Huber's New Observations Upon Bees, Bicentennial edition pg 219
"Two kinds of workers in the hive
"The following observations may also furnish indications of the presence of honey in the flowers. They are based upon a remarkable fact which was unknown to my precursors; it is that there are two kinds of workers in the hive; the ones which may attain a considerable size when they have filled themselves with all the honey that their stomach may contain, are in general destined to the elaboration of wax; the others whose abdomen does not perceptibly change in appearance, retain only the quantity of honey which is necessary for their sustenance and immediately hand out to others that which they have harvested; they are not in charge of the provisioning of the hive, their particular function being to care for the young: we will call them nurse bees, or small bees, in opposition to those whose abdomen may be dilated and which deserve the name of wax-workers.
"Although the external difference by which the two sorts may be recognized be inconsiderable, this distinction is not imaginary. Anatomical observations have taught us that there is a real difference in the capacity of their stomach. We have also ascertained that the bees of one sort cannot fulfill all the functions shared among the workers of a hive. In one of these tests we painted with different colors the bees of each class, to observe their behavior, and we did not see any interchange. In another test, we gave the bees of a queen-less colony both brood and pollen and we at once saw the small bees busy themselves with the food of the larvae, while those of the wax-working class paid no attention to them."-- Huber's New Observations Upon Bees, Bicentennial edition pg 219
