CCAP is responsible for activation of the ecdysis motor program. Fasting is sometimes an indication of an upcoming ecdysis (moult). Growth is accomplished by periodic shedding of the exoskeleton (ecdysis). Scientists suspect that these differences are associated with the colouration of the 4th larval ecdysis. Sensitivity to drought varies from species to species and increases during ecdysis. It follows the final ecdysis of the immature instars. The Ecdysozoa are protostomes, named after their shared trait of ecdysis, growth by moulting. Note that despite being internal, the tracheae of arthropods are shed during moulting (ecdysis). Development proceeds in repeated stages of growth and ecdysis (moulting); these stages are called instars. This shedding event occurs four times throughout development in a process called ecdysis. After hatching, the nymphs feed and undergo a series of 13 moultings (or ecdysis). Moulting is known as "ecdysis". Reptiles shed their skin through a process called ecdysis which occurs continuously throughout their lifetime. Although the process of ecdysis is metabolically risky and expensive, it does have some advantages. The exocuticle and epicuticle resist digestion and are hence shed at ecdysis.