About Locusts

Locusts are a type of insect that can be devastating pests of agriculture due to their ability to develop very large populations and to form dense and highly mobile swarms.

In Australia there are three main pest species of locust

All three species are native to Australia. Locusts belong to the same order of insects as grasshoppers, katydids and crickets - the Orthoptera.

Graphic: Adult Australian plague locust.

Many insects belonging to the order the Orthoptera can be readily identified
by their large back legs which enable them to hop or jump.

What is the difference between a locust and a grasshopper?

Locusts and grasshoppers are the same in appearance - how they differ is largely in their behaviour. Locusts can exist in two different behavioural states (solitary and gregarious) whereas grasshoppers generally do not. When the population density is low, locusts behave as individuals, much like grasshoppers. However, when locust population density is high, individuals undergo physiological and behavioural changes, known as phase polyphenism, and they form into gregariously behaving bands of nymphs or swarms of adults.

In addition to changes in behaviour, phase change may be accompanied by changes in body shape and colour, and in fertility, physiology, survival and migratory behaviour. These changes are so dramatic in some species that the swarming and non-swarming forms were once considered to be different species.

The distinction between locusts and grasshoppers is not clear-cut, as the extent to which different species exhibit gregarious phase characters is graded. The migratory locust has all of the features associated with phase change - differences in body shapes and colour, fertility and gregarious behaviour in both the nymphal and adult life stages, forming dense bands and swarms. The Australian plague locust has strong gregarious behaviour and forms dense bands and swarms, but does not exhibit changes in body colour. Spur-throated locust nymphs do not form bands and the adults do not lay eggs gregariously, but they do form dense swarms.

Some species that are called grasshoppers, such as Austroicetes cruciata, Oedaleus australis and Peakesia spp. can form loose swarms at high densities, but do not generally migrate long distances as locusts do.