Why do ant eggs/larvae/pupae (brood) taking so long to hatch into adult ants?

The speed of the egg to adult ant life cycle is heavily dependant on their surrounding temperature, but also your habitats humidity and the quality of food available (freshly crushed insects are best). The fastest brood development will take place during the heat of the summer. Brood development can grind to a halt over cold winter periods. Worker ants will move the brood to areas within your habitat that has optimum temperature and humidity. This means that it is good to have both moist and dry areas available so that the ants can choose where to go.