Royal Jelly

According to Wikipedia:

Royal jelly is a honey bee secretion that is used in the nutrition of the larvae. It is secreted from the hypopharyngeal glands in the heads of young workers and used (among other substances) to feed all of the larvae in the colony, including those destined to become workers. If a queen is needed, a larva is chosen and will receive only royal jelly — and in large quantities — as its food source for the first four days of its growth, and this rapid, early feeding triggers the development of queen morphology, including the fully developed ovaries needed to lay eggs.