Diet and digestion Most grasshoppers are
polyphagous, eating vegetation from multiple plant sources e.g pea plant leaves , but some are
omnivorous and also eat animal tissue and animal meat. They also like to eat other insects. In general their preference is for grasses, including many
cereals grown as crops. The digestive system is typical of insects, with Malpighian tubules discharging into the midgut. Carbohydrates are digested mainly in the crop, while proteins are digested in the ceca of the midgut. Saliva is abundant but largely free of enzymes, helping to move food and Malpighian secretions along the gut. Some grasshoppers possess
cellulase, which by softening plant cell walls makes plant cell contents accessible to other digestive enzymes. Grasshoppers can also be
cannibalistic when swarming.
Sensory organs '') showing the
compound eyes, tiny
ocelli and numerous
setae Grasshoppers have a typical insect nervous system, and have an extensive set of external sense organs. On the side of the head are a pair of large
compound eyes which give a broad field of vision and can detect movement, shape, colour and distance. There are also three simple eyes (
ocelli) on the forehead which can detect light intensity, a pair of antennae containing olfactory (smell) and touch receptors, and mouthparts containing gustatory (taste) receptors. At the front end of the abdomen there is a pair of tympanal organs for sound reception. There are numerous fine hairs (
setae) covering the whole body that act as mechanoreceptors (touch and wind sensors), and these are most dense on the antennae, the
palps (part of the mouth), and on the cerci at the tip of the abdomen. There are special receptors (
campaniform sensillae) embedded in the cuticle of the legs that sense pressure and cuticle distortion. There are internal "chordotonal" sense organs specialized to detect position and movement about the joints of the exoskeleton. The receptors convey information to the central nervous system through sensory neurons, and most of these have their cell bodies located in the periphery near the receptor site itself. Respiration is performed using
tracheae, air-filled tubes, which open at the surfaces of the thorax and abdomen through pairs of valved
spiracles. Larger insects may need to actively ventilate their bodies by opening some spiracles while others remain closed, using abdominal muscles to expand and contract the body and pump air through the system.
Jumping for a jump, overcoming the limitations of
muscle which cannot
contract powerfully and quickly at the same time. Representations of structure are diagrammatic. Grasshoppers jump by extending their large back legs and pushing against the substrate (the ground, a twig, a blade of grass or whatever else they are standing on); the reaction force propels them into the air. A large grasshopper, such as a locust, can jump about a metre (20 body lengths) without using its wings; the acceleration peaks at about 20 g. They jump for several reasons; to escape from a predator, to launch themselves into flight, or simply to move from place to place. For the escape jump in particular there is strong selective pressure to maximize take-off velocity, since this determines the range. This means that the legs must thrust against the ground with both high force and a high velocity of movement. A fundamental property of muscle is that it cannot
contract with high force and high velocity at the same time. Grasshoppers overcome this by using a
catapult mechanism to amplify the
mechanical power produced by their muscles. The jump is a three-stage process. First, the grasshopper fully flexes the lower part of the leg (tibia) against the upper part (femur) by activating the flexor tibiae muscle (the back legs of the grasshopper in the top photograph are in this preparatory position). Second, there is a period of co-contraction in which force builds up in the large,
pennate extensor tibiae muscle, but the tibia is kept flexed by the simultaneous contraction of the flexor tibiae muscle. The extensor muscle is much stronger than the flexor muscle, but the latter is aided by specialisations in the joint that give it a large effective mechanical advantage over the former when the tibia is fully flexed. Co-contraction can last for up to half a second, and during this period the extensor muscle shortens and stores elastic strain energy by distorting stiff cuticular structures in the leg. The extensor muscle contraction is quite slow (almost isometric), which allows it to develop high force (up to 14 N in the desert locust), but because it is slow only low power is needed. The third stage of the jump is the trigger relaxation of the flexor muscle, which releases the tibia from the flexed position. The subsequent rapid tibial extension is driven mainly by the relaxation of the elastic structures, rather than by further shortening of the extensor muscle. In this way the stiff cuticle acts like the elastic of a
catapult, or the bow of a bow-and-arrow. Energy is put into the store at low power by slow but strong muscle contraction, and retrieved from the store at high power by rapid relaxation of the mechanical elastic structures.
Stridulation Male grasshoppers spend much of the day
stridulating, singing more actively under optimal conditions and being more subdued when conditions are adverse; females also stridulate, but their efforts are insignificant when compared to the males. Late-stage male nymphs can sometimes be seen making stridulatory movements, although they lack the equipment to make sounds, demonstrating the importance of this behavioural trait. The songs are a means of communication; the male stridulation seems to express reproductive maturity, the desire for social cohesion and individual well-being. Social cohesion becomes necessary among grasshoppers because of their ability to jump or fly large distances, and the song can serve to limit dispersal and guide others to favourable habitat. The generalised song can vary in phraseology and intensity, and is modified in the presence of a rival male, and changes again to a courtship song when a female is nearby. In male grasshoppers of the family Pneumoridae, the enlarged abdomen amplifies stridulation. Female grasshoppers of the species
Chorthippus biguttulus appear to be able to integrate information from male calling songs. An unattractive song subunit far outweighs an attractive song subunit, and this asymmetrical integration is consistent with theories of
sexual selection because it helps females avoid potentially costly interaction with unsuitable mating partners if the song belongs to another species or indicates a low-quality male. The eggs in the pod are glued together with a froth in some species. After a few weeks of development, the eggs of most species in temperate climates go into
diapause, and pass the winter in this state. Diapause is broken by a sufficiently low ground temperature, with development resuming as soon as the ground warms above a certain threshold temperature. The embryos in a pod generally all hatch out within a few minutes of each other. They soon shed their membranes and their exoskeletons harden. These first
instar nymphs can then jump away from predators. Grasshoppers undergo
incomplete metamorphosis: they
repeatedly moult, each instar becoming larger and more like an adult, with the wing-buds increasing in size at each stage. The number of instars varies between species but is often six. After the final moult, the wings are inflated and become fully functional. The migratory grasshopper,
Melanoplus sanguinipes, spends about 25 to 30 days as a nymph, depending on sex and temperature, and lives for about 51 days as an adult. This causes the grasshopper to change colour, feed more and breed faster. The transformation of a solitary individual into a swarming one is induced by several contacts per minute over a short period. Following this transformation, under suitable conditions dense nomadic bands of flightless nymphs known as "hoppers" can occur, producing
pheromones which attract the insects to each other. With several generations in a year, the locust population can build up from localised groups into vast accumulations of flying insects known as plagues, devouring all the vegetation they encounter. The
largest recorded locust swarm was one formed by the now-extinct
Rocky Mountain locust in 1875; the swarm was long and wide, and one estimate puts the number of locusts involved at 3.5 trillion. An adult
desert locust can eat about of plant material each day, so the billions of insects in a large swarm can be very destructive, stripping all the foliage from plants in an affected area and consuming stems, flowers, fruits, seeds and bark. ==Predators, parasites, and pathogens==