- Written by Nadia O’Carroll
Locusts, grasshoppers, crickets and katydids belong to the Order Orthoptera; these are common insects with over 2,800 species in Australia.Locusts and grasshoppers belong to the Acrididae family, although species vary in colouring, size and shape they share some basic characteristics such as well-developed wings, short antennae and large powerful hind legs designed for jumping. There are over 700 species of Acrididae in Australia, only a small number of locust species are considered major pests.
Locusts and grasshoppers are identical in appearance but different in behaviour. Grasshoppers are essentially solitary insects but locusts can exist in two different states - solitary or gregarious.
When the locust population density is low, locusts behave individually in the same way as grasshoppers, their colours blend in with their surroundings, they have a low metabolic rate and are relatively sluggish and travel short distances at low altitudes during the day. When the population density is high, the crowded conditions cause a number of changes known as phase changes – body shape and size alter, locusts become brightly coloured, metabolic rate increases, their fertility alters and they become active and nervous. Rather than acting as individuals they swarm and migrate collectively.
The trigger for these major changes is the jostling that occurs when locusts crowd together, tactile stimulation of the locust’s back legs produces a sudden spike and increase in the serotonin levels and this causes mutual attraction, physical and behavioural changes. Serotonin is a neurotransmitter hormone which occurs in both plants and animals, it is involved in the transmission of nerve impulses and its production effects many physical aspects of an organism including body temperature, digestion, learning, memory, anxiety, mood, appetite, emotion and sleep. In humans it is associated with a happy feeling and many anti depressant, antipsychotic and psychedelic drugs work by altering or mimicking serotonin levels.
Grasshoppers and locusts have the same life cycle – the female drills a hole in the ground and lays a pod of eggs, they hatch into nymphs which moult through a number of stages or instars until the they become adults. When conditions are unfavourable for survival locust eggs may delay hatching and nymphs may have arrested development, when conditions improve these mechanisms are reversed and population explodes because several generations appear almost simultaneously.
Gregarious nymphs gather into high-density aggregations called bands, which move in fronts as the nymphs march collectively in the same directions. They develop into fledged adults with hard strong wings; they swarm and migrate in nocturnal wind assisted flights and may fly hundreds of kilometres at heights up to 1,000 metres. Locust swarms have been recorded travelling from West Africa to the Caribbean in 10 days a distance of 5,000 kms.