A bagworm begins to build its case as soon as it hatches. Once the case is built, only adult males ever leave the case, never to return, when they take flight to find a mate. Bagworms add material to the front of the case as they grow, excreting waste materials through the opening in the back of the case. When satiated with leaves, a bagworm caterpillar secures its case and pupates. The adult female, which is wingless, either emerges from the case long enough for breeding or remains in the case while the male extends his abdomen into the female's case to breed. Females lay their eggs in their case and die. The female evergreen bagworm ("Thyridopteryx ephemeraeformis") dies without laying eggs, and the larval bagworm offspring emerge from the parent's body. Some bagworm species are parthenogenetic, meaning their eggs develop without male fertilization. Each bagworm generation lives just long enough as adults to mate and reproduce in their annual cycle.