eclosion
noun
eclo·sion i-ˈklō-zhən 
of an insect
: the act of emerging from the pupal case or hatching from the egg
Word History
Etymology
borrowed from French éclosion, from éclos-, variant stem of éclore "to hatch (from an egg), emerge (from a cocoon)" (going back to Old French esclore, going back to Vulgar Latin *exclaudere, re-formation of Latin exclūdere "to bring out from its container, hatch from an egg") + -ion -ion — more at exclude
First Known Use
circa 1889, in the meaning defined above