During June and July, eggs of the Five-lined Skink (Plestiodon fasciatus) hatch, producing tiny black and white striped offspring with metallic blue tails. These small lizards are often common in yards, on logs in the forest, and on the sides of trees. When approached, they rapidly disappear into leaf litter or under a log. What we often see is just a blur of blue.
The black and white stripes fade as the skinks get older, and just after they reach sexual maturity, their tails fade to match the brown body coloration. Why are the juveniles so brightly colored in the first place, and why do they lose this coloration?
If you watch a young skink for a while, it will go in and out of leaf liter looking for small insects. When its body goes into the leaf litter, it will move the tail back and forth on the leaf litter. If a bird or other predator has been watching the lizard, the blue tail signals that the skink knows a predator is near and that it likely can escape if attacked. If the bird attacks anyway, it may get the tail but the lizard will escape and grow a new tail. Losing a tail doesn’t cost a young skink very much in terms of energy. So this is the answer to the first question. The bright coloration distracts a predator away form the body of the skink to the tail, which can be re-grown if lost.
As these skinks grow and lose their juvenile coloration, they tend to become cryptic. That is, they match the background colors of the forest and are much more difficult to see. They are also more experienced because they are older. Adults store fat in the tail, and that fat is used by males for reproductive related behavior, and by females, to produce eggs. As a result, losing a tail as an adult is expensive energetically and it can affect their ability to reproduce in a given year. They also can grow back their tails if they should lose them, but they might have to skip a year of reproduction. Consequently, the tail in adults is an important fat storage organ, so good reasons exist to not attract attention to it.