Natural history
- Related Topics:
- ice bug
- phasmid
- Orthoptera
- Dictyoptera
- Exopterygota
Life cycle
General features
Since orthopterans undergo simple metamorphosis and have externally developing wings, they are known as hemimetabolous insects. A typical orthopteran life cycle has three stages: egg, nymph, and adult. Usually eggs are deposited outside the body on the ground or on vegetation. Nymphs resemble adults except for their smaller size and lack of development of reproductive organs and wings; there is no pupa, or resting stage. In most orthopteran groups, the hatching insect that wriggles from the egg is not a fully formed nymph with freely moving legs; actually it is little more than an active embryo and is still enclosed in a thin membrane. This stage is called a vermiform larva; shedding of the enclosing membrane occurs at the intermediate molt. The shapeless skins shed by young grasshoppers crawling from egg pods are examples of such exuviae (cast skins).
The number of nymphal stages between the intermediate molt and adulthood varies from about 4 to 13. Generalizations are approximately as follows:crickets and katydids, 5–9; and grasshoppers, 4–9, most often 5–7.
Egg laying
Egg-laying habits are distinctive in many orthopteran species. Crickets and katydids utilize their ovipositors to insert eggs into soil or plant material. The eggs of tree crickets (Oecanthus), for example, are inserted in rows in the canes of blackberries and various other stems; the eggs of field crickets (Gryllus) are laid in soil; the flattened eggs of certain katydids (Scudderia) are forced between the upper and lower epidermis layers at the margin of tree leaves; and the eggs of other katydids (Microcentrum) are laid in overlapping rows lengthwise on twigs of trees.
Most grasshoppers lay their eggs in soil; a few drill holes in dead wood or place their eggs at the bases of grass clumps or on the surfaces of leaves. Before laying the eggs, the female manipulates the valves of her ovipositor to make a hole in suitable soil (the type varies with the species). During the digging process, the abdomen is greatly extended, and the female manipulates the ovipositor valves to open and close and rotate on the long axis. Then she deposits several dozen eggs in the hole. The eggs are surrounded by a mucilaginous mass (the egg pod) that dries in a cylindrical shape. The number of egg pods laid by one female and the number of eggs in each pod vary according to the species and local conditions. The egg pods are laid over an interval of several weeks.
A few orthopteran species have females only; therefore, reproduction occurs without fertilization (parthenogenesis). Only rarely are species that normally reproduce bisexually parthenogenetic; and when parthenogenesis does occur in bisexual species, it is usually only partially successful because the few nymphs that do hatch often are deformed and fail to reach maturity. In the laboratory, however, there have been a few cases in which several generations have been produced parthenogenetically, proving that there is an inherent capability in these bisexual groups for reproduction without males.