Grasshoppers are herbivorous insects of the suborder Caelifera in the order Orthoptera. Twenty four hundred valid Caeliferan genera and about 11,000 valid species are known as Caelifera. Still, many undefined species exist especially in tropical wet forest. To distinguish them from the suborder Ensifera (bush crickets or katydids) which looks almost the same, they are sometimes referred to as short-horned grasshoppers. Locusts are the species that change colors and behaviors at high population densities. Most grasshoppers are green, brown, or olive-green. Females are usually larger than males, with short ovipositors which is an organ where sperm is deposited. While the size of grasshoppers ranges from 5mm to 100mm, the largest are about 11.5 cm long.
The Caelifera suborder is distinguished from Ensifera by following things.
- The structure of the ovipositor is reduced to 4 functional valves with transverse musculature from the original 6 valves.
- Antennae are composed of less than 30 segments.
- The auditory organs are on the first segment of the abdomen.
- The sperm are thin and elongate, with an acrosome inserted on the nucleus by means of two lateral processes.
- Males produce their love song to females by lateral part of their forewings.
Like all insects, the grasshoppers have a three-part body (head, thorax and abdomen), three pairs of jointed legs, two pairs of wings, and one pair of sensory antennae. Their hind legs, which are good for jumping, are highly developed, much stronger and larger than the other four legs. Tegmina, the front wings, which are tough and narrow compared to the hind wings cover and protect the hind wings. But flight is mainly achieved by the hind wings and the tegmina give only little help. Most grasshoppers have antennae that are shorter than their body, and short ovipositor which is an organ at the end of the abdomen, by which eggs are deposited. Since the grasshoppers don’t have vertebral column or backbone, their body is covered with a hard exoskeleton. Grasshoppers breathe through spiracles; a series of holes located along the lateral sides of the body. 
Grasshopper reproduction depends mostly on quality and quantity of food. Protein seems to be most important for insect survival, growth and reproduction.  When mating begins, the male grasshopper passes sperm into the vagina through its aedeagus which is a reproductive organ, and inserts its spermatophore, a package containing the sperm, into the female's ovipositor. The sperm enter the eggs by passing through fine ways called micropyles. Then the female lays the fertilized egg pods by using her ovipositor and abdomen. Although she can lay egg pods in plant roots or even manure, she inserts the eggs about one to two inches underground. Several dozens of tightly-packed eggs that are contained in the egg pods look like thin rice grains. The eggs stay where they are laid throughout the winter, and hatch when the weather has warmed up sufficiently. Many grasshoppers spend most of their life as eggs (up to 9 months) and only spend a short part of their life in active states (up to 3 months). The first nymph to hatch digs up through the ground, and the nymphs that hatch later follow. When young grasshoppers grow, they develop through stages progressively by getting larger in body and wing size. Since the young are similar to the adult, grasshoppers are referred as hemimetabolous or incomplete development.
Grasshoppers play an important role in grassland ecosystems; being food for wildlife and contributing to the food chain. Grasshoppers live in non-marine habitats where plants can live (including deserts, water surfaces, grasslands, underground, or the crowns of forest trees). They usually consume a wide range of plants such as mosses, algae and leaves. Grasshopper outbreak can cause much damage to crops and forage. But out of 400 species, only fewer than 2 dozen cause significant economic damage to crops and forage. Their predators are birds, beetles, rodents, reptiles, and spiders. Grasshopper eggs are food for some flies.
Locusts are the short-horned grasshoppers of the family Acrididae. Locusts exhibit two different lifestyle behaviors (solitary and gregarious). When the population density is low, locusts behave as individuals. However, when the population density is high, they form into outgoing behaving bands of nymphs or swarms of adults. This change of behaviors is known as phase change which can be also accompanied with change in colors. They are the insects that spread devastating pests and are critical to agriculture due to the phase change. 
- Grasshopper by Wikipedia
- Grasshopper characteristic by Tree of Life
- Grasshopper anatomy by Geosociety
- Grasshopper anatomy by Enchantlearning
- Grasshopper reproduction by Grasshopper Biology
- Locusts by Australian Government
- Grasshopper Identification Guides / Fact Sheets / Field Guides by the USDA & ARS