Australian Plague Locusts - Frequently Asked Questions
Locust biology
What is an Australian Plague Locust?
A locust is a type of insect similar to grasshoppers, katydids and crickets - the Orthoptera (derived from the Greek words orthos meaning straight or rigid and ptera meaning wing).
The Australian Plague Locust is a native species that occurs naturally in the far north west of New South Wales and adjacent areas of Queensland and South Australia. It is one of many locust species.
Locusts are similar in appearance to grasshoppers.
For more information, read the Identification and Biology of an Australian Plague Locust fact sheet or view the Locust Videos on the DPI website www.dpi.vic.gov.au/locusts
How is a locust different to the common grasshopper?
There has been some difficulty distinguishing the Australian plague locust from the wingless grasshopper and a number of other locust and grasshopper species.
Adults of the Australian plague locust are distinguished from other species by the large dark spot on the tip of the hindwings and distinctive scarlet line on the tibia (2nd segment from the body) on the hind legs.
The hind wings are clear with no other colouration or marking apart from the translucent black area at the tip of the wing.
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| Adult Australian Plague Locust – showing red shank on leg |
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Plague locust adult showing the black spot on the hind wing |
Why are locusts pests?
The ability of locusts to form into dense aggregations as hoppers (bands) or adults (swarms) make them formidable eating machines that can rapidly devastate crops.
The highly mobile nature of swarms and their ability to migrate over large distances means that virtually all agricultural areas are at risk from damage.
What damage can they cause?
Adult locusts and hoppers can cause extensive damage to crops and pasture in a relatively short timeframe. Locusts prefer to feed on tender, green vegetation, but experience shows they are still capable of causing damage to maturing and mature crops. When locusts are present in large numbers, all crops are at risk.
A locust swarm could also severely disrupt outdoor activities like sporting or community events and cause a hazard on our roads.
Where do locusts lay their eggs?
Female locusts can lay up to 200 eggs in pods that contain about 30-40 eggs. Eggs are often laid up to 10 cm beneath the soil in bare ground, generally along roadsides, tracks, fence lines, dry land flats and sparse pastures and paddocks. Usually eggs laid in autumn are dormant over winter and hatch in spring as soil temperatures increase.
What is an egg bed – and how do I recognise it?
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Exposed locust egg bed |
Locusts usually lay eggs on bare damp dirt. Female locusts may crowd together and lay large numbers of eggs in a patch of soil suitable for egg laying. These areas are referred to as egg beds. The eggs are buried below the surface.
Egg beds are most easily detected while the locusts are laying eggs. While female locusts are laying eggs and have their abdomen poked into the soil they do not disturb and fly away as rapidly as normal. If egg laying is not observed it is difficult to know the location of egg beds prior to eggs hatching.
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Adult locusts laying eggs |
The ground where the eggs have been laid looks like a sieve with lots of shallow holes that are very close together. Female locusts will often make test drill holes in the soil without laying any eggs. When looking for egg beds, care needs to be taken to ensure that sites where locusts have been test drilling are not mistaken as egg beds and the actual extent of egg laying is then over-estimated.
People trying to identify locust egg beds should therefore dig up clods of soil where locusts are seen drilling, or where holes are evident and directly inspect the actual density of locust eggs in the soil. Within the short period after egg laying, the holes created during laying may fill with loose dirt from the surface very quickly removing all traces of egg laying within as little as two to three hours after the event.
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Example of a shovel used to dig up egg beds |
Are eggs always laid in egg beds?
No. When the adults are in low density, and in some other situations, egg laying may be scattered across an area.
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Exposed locust egg bed |
How many eggs does a female locust lay?
Each female lays pods of 30 eggs sometimes laying only one pod per life time, but can lay up to five pods.
Pods are laid at five to seven day intervals.
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Adult female laying eggs |
What causes locusts to hatch?
Egg development occurs only in warm moist conditions. Given sufficient moisture and at a daily maximum of 35°C, egg development takes just over two weeks, while with a daily maximum of 25°C, it takes over a month. Egg development does not take place below about 15°C.
Will cooler weather conditions delay locust growth?
Wild weather conditions across the state have had the twin impact of delaying spraying activity but also slowing the development of locusts as temperature has a major effect on both locust development, their feeding and movement.
Cooler temperatures will slow locust development markedly and the time for complete nymphal development can double with a drop in average temperatures of as little as three degrees at the cooler end of the scale, say around 20°C.
There may also be higher mortality of nymphs with cooler temperatures as locusts are slower and may be more easily taken by predators such as birds.
These conditions will have implications for spraying and treatment as development is slower, the aggregation and banding may be delayed thus delaying optimum control timing in some situations.
Monitoring will be more difficult in wet weather and locusts will be less active and therefore less obvious. Landholders could take this opportunity to ensure equipment is prepared and ready for when weather is more favourable.
For further information on temperature for your area, read the joint DPI and Bureau of Meteorology factsheet to help you use the Bureau’s Forecast Explorer Tool.
What happens when they hatch?
From each egg, an immature locust emerges, called a nymph or more commonly a hopper. As the hoppers grow and develop, they pass through five, and in some circumstances six, stages of development called instars.
The hoppers moult between each instar to enable their body to expand. In mid summer, the hoppers take around 20-25 days to complete their development before maturing to become adult locusts that are capable of flight.
Australian plague locusts may disperse either by walking whilst hoppers or by flight as adults. At higher densities, the hoppers may form dense groups known as bands that move across an infested area en masse stripping the vegetation.
Similarly, adult locusts can also form large groups called swarms which may invade and defoliate infested plants.
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Hoppers hatching |
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Hoppers hatching |
Where will they spread?
Flight is the main method by which locusts spread over large distances. This can occur to a limited extent during the day and more commonly, over much larger distances at night. The extent of migration will depend on a number of factors such as the availability of food, density of locusts and weather conditions.
The direction of spread, especially night time long distance migration, depends on prevailing wind directions with the extent of spread determined by the strength and duration of the wind. It is possible for locusts to travel up to several hundred kilometres per night.
What do they eat?
Most species of locust feed mainly on grasses. The Australian Plague Locust in particular prefers to feed on grasses and/or cereal crops such as wheat.
However, when there is little green grass available they will eat a wide range of plants including: horticulture crops, pasture, grapevines and trees.
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Locust band in dry grass |
Will locusts attempt to eat synthetic material including synthetic grass?
Yes, locusts are attracted to the colour green. There is anecdotal evidence that suggests locusts will eat many things including green coloured shadecloth, and it may be possible that they may target synthetic grass.
Locusts would only attack this type of material if green vegetable matter or cereal crops are not available.
If you are concerned about your synthetic grass, i.e. tennis court, you should seek advice from the manufacturer about covering the court when locusts are swarming, for example, a layer of sand might provide some protection.
Will locusts eat gum leaves?
Mature gum leaves are not a preferred feeding option for locusts, but they might still be threatened if alternative food sources are unavailable.
However, young tree seedlings are especially susceptible to attack from locusts, and severe damage could set back the trees growth.
Why is the full extent of their egg-laying unclear?
Egg beds are difficult to detect unless female locusts are observed during egg laying. The full extent of egg laying does not become apparent until the eggs begin hatching and the hoppers, which are more easily detected, emerge and become active.
