Phasmatodea
Life cycle

The life cycle of the stick insect begins when the female deposits her eggs through one of these methods of oviposition: she will either flick her egg to the ground by a movement of the ovipositor or her entire abdomen, carefully place the eggs in the axils of the host plant, bury them in small pits in the soil, or stick the eggs to a substrate, usually a stem or leaf of the food plant. A single female lays from 100 to 1,200 eggs after mating, depending on the species.

Many species of phasmids are parthenogenic, meaning the females lay eggs without needing to mate with males to produce offspring. Eggs from virgin mothers are entirely female and hatch into nymphs that are exact copies of their mothers. Stick insect species that are the product of hybridisation are usually obligate parthenogens, but non-hybrids are facultative parthenogens, meaning they retain the ability to mate and their sexual behavior depends on the presence and abundance of males.

Phasmatodea eggs resemble seeds in shape and size and have hard shells. They have a lid-like structure called an operculum at the anterior pole, from which the nymph emerges during hatching. The eggs vary in the length of time before they hatch which varies from 13 to more than 70 days, with the average around 20 to 30 days. Some species, particularly those from temperate regions, undergo diapause, where development is delayed during the winter months. Diapause is initiated by the effect of short day lengths on the egg-laying adults or can be genetically determined. Diapause is broken by exposure to the cold of winter, causing the eggs to hatch during the following spring. Among species of economic importance such as Diapheromera femorata, diapause results in the development of two-year cycles of outbreaks.

Many species' eggs bear a fatty, knoblike capitulum that caps the operculum. This structure attracts ants because of its resemblance to the elaiosome of some plant seeds that are sought-after food sources for ant larvae, and usually contribute to ensuring seed dispersal by ants, a form of ant-plant mutualism called myrmecochory. The ants take the egg into their nest underground and can remove the capitulum to feed to their larvae without harming the phasmid embryo. There, the egg hatches and the young nymph, which initially resembles an ant (another instance of mimicry among Phasmatodea), eventually emerges from the nest and climbs the nearest tree to safety in the foliage. The eggs of stick insects have a coating of calcium oxalate which makes them survive unscathed in the digestive tract of birds. It has been suggested that birds may have a role in the dispersal of parthenogenetic stick insect species, especially to islands.

The Phasmatodea life cycle is hemimetabolous, proceeding through a series of several nymphal instars. Once emerged, a nymph will eat its cast skin. Adulthood is reached for most species after several months and many molts. The lifespan of Phasmatodea varies by species, but ranges from a few months to up to three years.
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