Grasshoppers, crickets, katydids and locusts: Order Orthoptera

Grasshoppers, locusts, crickets and katydids belong to a group of insects known as orthopterans (meaning 'straight wings').

Most people have encountered grasshoppers at some time and seen them hop away or leap into a short low flight. Similarly, most of us have heard the sound of crickets at night as the males call out for mates. Grasshoppers and crickets are related and together with the katydids and locusts, make up the Order Orthoptera (meaning 'straight wings').

One of the most recognisable features of this group is their ability to produce sounds by rubbing together certain parts of their body. This is known as stridulation. Usually only the males sing to attract females but, in a few species, the female also produces sound.

Grasshoppers and locusts have a row of pegs like a comb on their back legs. They scrape these pegs against the hard edges of the front wings to make sounds. Crickets and katydids produce sounds by rubbing their wings together. In order to hear these sounds, orthopterans have a tympanum (ear) on each front leg, just below the knee.

There are about 3,000 species of orthopterans in Australia and they have the following features:

• powerful hind legs for jumping
• metamorphosis from wingless nymph to winged adult
• ability to produce sounds
• antennae that may be long and thin, or short depending on the species
• chewing mouthparts (most species are vegetarian but a few crickets feed on other insects).

Identification

Members of the Orthoptera are usually large bodied insects with the enlarged rear legs adapted for jumping. The rear legs often face backward alongside the body in preparation for a leaping escape from a predator, though some groups have lost the capacity for jumping. Many Orthoptera produce sounds, usually made by males to attract females, by rubbing their forewings together. These sounds can also be made by rubbing their legs against the body or the wings, or by grinding their mandibles (jaws).

The suborder Ensifera, which contains the true crickets, mole crickets, king crickets and katydids, can usually be recognised by the long antennae that may be several times the length of the body. Locusts and short-horned grasshoppers belong in the other suborder, Caelifera, and have shorter and more robust antennae.

Habitat and Biology

Members of the Order Orthoptera display a wide range of food preferences, habitat types, reproductive strategies and behaviours.

Many crickets live in burrows during the day. Raspy crickets (Family Gryllacrididae) construct shelters with material bound together by silk or maintain silk-lined burrows. These crickets often leave their shelters at night to forage. During the day they seal the entrance shut with silk to avoid desiccation (drying out). True crickets (Family Gryllidae) may live in burrows, crevices in the soil, in logs or under leaf litter.

Katydids and tree crickets all belong to the family Tettigoniidae. The family is very large, containing approximately 1000 described species in Australia, with many more undescribed. Its members display a variety of habitat and dietary preferences. Katydids feed on pollen and nectar, vegetation, insects and invertebrates. The family is found throughout Australia.

Locusts and grasshoppers (Suborder Caelifera, Family Acrididae) are very common insects. However, locusts behave differently depending on their numbers. When numbers are low they act as individuals, in the same way as grasshoppers. But when large numbers are present they behave as a group or swarm, causing plagues.

Locusts such as the Australian Plague Locust (Chortoicetes terminifera), the Spur-throated Locust (Austracris guttulosa) and the Migratory Locust (Locusta migratoria migratoriodes) can form plagues that cause massive damage to agricultural crops. Locust plagues usually occur when the right rainfall conditions enable several generations to reproduce in large numbers. The Australian Plague Locust Commission conducts regular surveys and research to combat the outbreak of plagues.

Both locusts and grasshoppers feed on mainly grasses, but many other plants are also eaten. Both are eaten by a wide variety of animals and parasitised by mites, worms and other insects such as the wasps of the genus Scelio, which parasitise the eggs. In some parts of the world locusts are eaten by people.

Mole Crickets (Family Gryllotalpidae) are common in well-watered urban parks and gardens. Using their large forelegs, male mole crickets dig specially constructed burrows which act as amplifying 'horns'. These flightless males can be heard at dusk during the warmer months making a very loud, continuous call using their modified wings. The calls help the flying females locate the males for mating. Mole crickets are the only crickets where the females can also call (but not as loudly as the males).

Sand Gropers (Family Cylindrachetidae) are large burrowing orthopterans, mostly found in Western Australia. One species is an occasional pest of wheat crops. Both sexes are wingless and rarely emerge above ground.

The Dingo or Cooloola Monsters (Family Cooloolidae) are an endemic Australian family found in the sandy coastal parts of Queensland (the first specimens were found around Cooloola). They are burrowing insects that cannot fly. They have been called 'monsters' because of their large robust bodies and strongly clawed forelegs. Only three species have been described so far, as they are rarely found.

Reference

• Rentz, D. 1996. Grasshopper Country. UNSW Press: Sydney