Young females will only produce one clutch of three to sixteen eggs, while a large female can produce up to four. The eggs take approximately ten weeks to hatch and emerge near the end of summer. The young lizards grow quickly and are able to reproduce the next year. Unfavorable nesting conditions can cause females to retain their eggs longer than they would have otherwise. This phenomenon is referred to as egg retention. Egg retention in the eastern fence lizard produces heavier eggs with more advanced embryos and with higher posthatching survival rate, but does not influence phenotype. Greater reproductive energy allocated to first clutches is common at higher latitudes, whereas more energy is dedicated to later clutches in lower latitudes. Embryonic development After the eggs are laid by a female, the development of the embryo and yolk within differ from that of birds, which has long been assumed to be identical. Instead, the process is more similar to snakes. Strands form a vascularized network within the yolk sac cavity. The embryo and yolk sac cavity then progress through three distinct developmental stages. In the first stage, endodermal cells develop and invade the nourishing yolk in order to digest it. They may clump within and begin filling the cavity. In the second stage, the vasculature of the yolk sac produces blood vessels that expand throughout the cavity. In the third stage, the cells organize themselves around the blood vessels. They can now more quickly and easily digest yolk. The products of digestion reach the embryo via release into blood vessels. Escape response to fire ants The pressures of predation can select for a variety of escape tactics. In their natural habitat, these lizards encounter invasive ants, red imported fire ants (Solenopsis invicta), the bites of which threaten the lizards with envenomation and, possibly, reduced growth in juveniles. Fire ants also compete with eastern fence lizards for their nesting habitats and predate on their eggs. These encounters can be dangerous and even lethal to the lizards. When attacked by these stinging fire ants, fence lizards twitch their bodies to throw off the attacking ants before fleeing. The learning of these lizards after repeated exposure to fire ants has also been studied. Lizards that were more familiar or exposed to attacking fire ants tend to twitch more and flee sooner compared to lizards that were not exposed. This may also be an