After hatching from eggs, bed bugs go through several stages of growth as juveniles, called nymphs.
There are five nymphal stages before a bed bug becomes a fully grown adult. Each stage requires molting or shedding of the shell to enter the next stage. Each stage is called an instar so that the stages can be termed first instar nymph, second instar nymph, etc.
Nymphs feed on blood
After hatching from the egg which is approximately 1/32” long, the first instar nymph is nearly as long as the egg and almost clear in color so that they are nearly invisible due to their size and color. In order to move to the next instar, the nymph must feed on blood, preferably human blood. Each nymph may feed multiple times before they move to the next instar stage. Usually, bed bugs will feed from three to ten minutes to repletion. They can also feed a few seconds and move to feed at another location on the host.
Later stages of development
As the nymphs reach later stages, they can be seen. Early instar nymphs will be the color of blood after feeding since they have no color of their own. Later instars may appear to be a brownish color even before feeding. Late stage instars resemble adult bed bugs. It is important to note that nymphs do in fact feed on blood and they are difficult to find in an infestation. It is also important to understand that bed bugs feed on nothing other than blood so infestations are possible anywhere humans are from homes to hotels to libraries to movie theaters.