Frequently asked questions about locusts
What is a locust?
Are locusts native to Australia?
Why are locusts pests?
Why do plagues occur?
Where do plagues occur in Australia?
When was the first plague in Australia?
Did plagues occur in Australia before European settlement?
Has clearing vegetation increased the incidence of plagues?
Has global warming increased the incidence of plagues?
Are locust numbers associated with El Nino or La Nina events?
How many locusts are there in a swarm?
Where do locusts go when there are no plagues?
What do locusts eat?
How much does a locust eat?
Do locusts eat everything in their path?
Do locusts eat anything green?
What is the role of the APLC?
Why doesn't the APLC control in WA?
Why doesn't the APLC control all grasshopper pests?
What is the economic impact of locusts?
How does the APLC control locusts
What control strategy does the APLC use?
Are locust control agents harmful?
What risks do locust control agents pose?
Does the APLC use natural methods of control?
Why not collect locusts for animal feed?
How far can a locust fly in a day?
How many eggs does a locust lay?
How long does a locust take to develop?
What species of locusts are pests?
Do people eat locusts?
1. What is a locust and how do they differ from grasshoppers? A locust is a type of insect belonging to the same order as grasshoppers, kaytdids and crickets - the Orthoptera (derived from the Greek words orthos meaning straight or rigid and ptera meaning wing). Locusts are identical in appearance to grasshoppers with which they share the family Acrididae. The only difference between the two types of insects is that locusts can exist in two different behavioural states (solitary and gregarious) whereas grasshoppers do not. When the population density is low locusts behave as individuals, much like grasshoppers. However, when the population density is high, locusts form highly mobile gregariously* behaving bands of nymphs or swarms of adults.
[*living in flocks or communities; growing in clusters]
2. Are locusts native to Australia? Yes. Of the three main pest species in Australia, only the Australian plague locust (Chortoicetes terminifera) is confined in distribution to Australia. The spur-throated locust (Austracris guttulosa) is also found in Indonesia, the Philippines, Papua New Guinea and offshore islands. Various subspecies of the migratory locust (Locusta migratoria) are found virtually throughout the warmer regions of the Old World.
3. 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. Also, 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.
4. Why do locust plagues occur? In general, major outbreaks or plagues occur when widespread rain falls throughout the year allowing successive generations of locusts to breed in high numbers. For a more detailed explanation see the About Locusts page.
5. Where do locust plagues occur? Locust plagues can occur anywhere in mainland Australia. The area affected by a plague is largely dependent on where significant rain has fallen and which way the wind displaces migrating swarms. Outbreaks of the Australian plague locust are particularly frequent in inland areas of Queensland (Qld), New South Wales (NSW) and South Australia (SA). In some years swarms of the Australian plague locust reach cropping areas of Victoria (Vic) or eastern Queensland. Outbreaks in Western Australia (WA) are infrequent but plagues do occur. The Great Dividing Range acts as a natural barrier to migrating locusts, protecting coastal areas of eastern Australia from invasion, although populations occasionally establish in cleared valleys, such as the Hunter Valley in NSW. Areas of higher rainfall also have fewer locust problems because parasites and diseases are able to keep their numbers in check. For more information see the About Locusts page.
6. When was the first recorded locust plague in Australia? 1844 is the earliest written record found. An unidentified species of locust was reported invading Adelaide and it is most likely that these were Australian plague locusts. Other outbreaks recorded in NSW and SA throughout the late 1800s were a mixture of the Australian plague locust and the small plague grasshopper (Austoicetes cruciata). For more information on the history of locust plagues in Australia see About Locusts.7. Did locust plagues occur in Australia before European settlement? Locusts and their ancestors have been present in Australia for millions of years. In that time they have evolved the best strategies for living in the harsh Australian environment. Locust plagues are a natural phenomenon which occur when conditions are ideal for breeding over successive generations (see FAQ 4). It wasn't until the introduction of the European system of agriculture in the late 1800s that locusts became an economic issue and a threat to peoples' livelihood.
8. Has the clearing of native vegetation increased the frequency of locust and grasshopper outbreaks in Australia? In the case of the migratory locust, Locusta migratoria in eastern Queensland, clearing of natural forest and woodland and establishment of introduced pastures and crops may have increased outbreak frequency. Plagues of this species were not recorded before the 1970s. Widespread clearing of brigalow scrub from the 1950s onwards has increased the area of suitable habitat for locust breeding. Also, the severity of outbreaks of the wingless grasshopper have increased over the last five decades due to the expansion of improved pastures on the western slopes and tablelands of NSW.
Land clearing in the woodlands of western NSW and Qld has also increased the area of available breeding habitat for the Australian plague locust, but it is difficult to determine if this has affected the frequency of outbreaks, through a feedback of larger spring populations. Infestations were not recorded in the central west of NSW, or in the Hunter Valley until after woodlands were cleared in the late 1890s. Conversely, it is believed that changes in land use may have decreased the frequency of outbreaks of other species of locusts and grasshoppers such as the plague grasshopper in Western Australia and the yellow-winged locust in Queensland.
9. Has global warming increased the frequency of locust plagues around the world? There is no strong evidence for this. Recent outbreaks of locusts in many parts of the world are more likely to be linked to above average rainfall associated with normal, but largely unpredictable climatic cycles.
10. Are fluctuations in locust numbers in Australia associated with El Ni?o or La Ni?a events? In Australia, strong El Ni?o* and La Ni?a* events have some influence on locust numbers but cannot entirely explain the incidence of plagues. Locust plagues sometimes do, but not always, occur when there is a strong La Ni?a event as this is associated with above average rainfall. However, above average rainfall may not necessarily lead to a locust outbreak, as the critical factor in the development of a plague is the timing of rainfall events in relation to breeding (see FAQ 4).
[*for a definition of El Ni?o and La Ni?a events see the Australian Bureau of Meteorology Climate Glossary]
12. Where do locusts go when there are no plagues? When conditions are dry, locusts persist in low numbers but are rarely noticed. At low densities locusts behave as individuals, like normal grasshoppers, and do not form into dense aggregations. There is always a background population remaining somewhere in Australia, even during the driest of years, from which numbers can rapidly rebound when conditions improve. The eggs of the Australian plague locust can survive in the soil for many months until rain falls.
13. What do locusts eat? Most species of locust feed mainly on gramineous plants (plants belonging to the grass family). The Australian plague locust in particular prefers to feed on grasses and/or cereal crops such as wheat. However, they will eat a wide range of plants including grapevines and trees, especially when there is very little green grass available.
14. How much does a locust eat in a day? An Australian plague locust eats approximately one third to one half of its body weight per day throughout its life. Therefore, a mature adult Australian plague locust may eat about 0.2 grams (g) of vegetation per day on average. Densities of adult Australian plague locusts in settled swarms usually range from about 4 to 50 metres (m)2. Therefore, a swarm covering an area of 1km2 would eat between 0.8 and 10 tonnes of vegetation in one day, depending on locust density.
Larger species of locusts can consume much greater volumes of vegetation; for example the Desert locust (Schistocera gregaria) of Africa and Asia may eat about 1.5 g of vegetation per day. This species also occurs in much denser swarms than the Australian plague locust. A high density swarm of Desert locusts covering an area of 1km2 could eat about 200 tonnes of vegetation in one day.
15. Do locusts eat everything in their path? Locusts when in plague proportions are often depicted as ravaging vast areas of countryside eating everything in their path. However, devastation on such a large scale and intensity is extremely rare. Bands of hoppers can do extensive damage to pasture and young cereal crops in spring (see photo) but as the locusts cannot fly at this stage damage is limited to the immediate area. Swarms of adult locusts are highly mobile and they will often do severe damage to part of a crop (particularly along the edge) before moving on elsewhere. The behaviour of a swarm is highly unpredictable and sometimes they will fly over apparently suitable crops without inflicting damage. Damage to crops is often worse when conditions are very dry and they are the only green vegetation remaining. When there is an abundance of green grass, the threat of damage to crops is often reduced (see also FAQ 20).
16. Is it true that locusts will eat anything green? Stories of locusts stripping green paint off walls or water tanks, eating green clothes hanging on a washing line or destroying green shade-cloth have been circulating for a number of years but their incidence and severity are often greatly exaggerated. Colour is only one of many cues that locusts use to identify suitable sources of food. When a swarm passes over an area, locusts may land and settle on any object in their path. Normally, if they do not land on palatable vegetation they will move on to seek a suitable source of food. However, under very dry conditions, when green vegetation is unavailable and the locusts face starvation, they may temporarily feed on any green object but the level of damage is rarely of significance.17. What is the role of the Australian Plague Locust Commission (APLC)? The Australian Plague Locust Commission (APLC) was established in 1974 to overcome past difficulties in organising the control of an insect that migrates over long distances and poses an interstate threat to agricultural industries. The Commission is jointly funded by the Commonwealth (50%), New South Wales (32.5%), Victorian (10%), South Australian (5%) and Queensland (2.5%) governments. Our role is to: a) manage outbreaks of the Australian plague locust, spur-throated locust and migratory locust that are considered to be an interstate threat; b) assist States to manage locust outbreaks in their area of responsibility and c) seek to improve the effectiveness and safety of locust field operations.
18. Why doesn't the APLC control locusts in Western Australia? WA elected not to become a member State as locust plagues in WA are infrequent and do not pose an interstate threat to agriculture. Control of locust plagues in WA falls under the responsibility of landholders and WA Department of Agriculture and Food.
19. Why doesn't the APLC control all pest species of locusts and grasshoppers? Other pest species of locusts and grasshoppers in Australia have a very low or no migratory capacity and do not therefore pose an interstate threat to agriculture. Usually landholders are responsible for the control of these non-migratory species but State governments may assist when infestations are widespread. The APLC may assist in the control of other locust pests, both within and outside Australia, when help is requested but only if staff are available. Research & development conducted by the APLC is transferred to other State and overseas organisations involved in locust and grasshopper control. Notable APLC successes include a significant reduction in the rate of insecticide needed to control locust infestations, the development of a Decision Support System to help monitor and control locusts and the development of a biological control agent called Metarhizium. For further details see APLC Research and APLC Extension.
20. What is the economic impact of locusts in Australia? The economic impact of locusts depends on many factors including: the size of the outbreak, the intensity of agricultural production in the outbreak area, the timing of the outbreak in relation to the stage of crop development and seasonal weather. The very severe 1934 locust plague caused an estimated loss of ?3.6 million in NSW alone (equivalent to over A$60 million). In contrast, during the large 1973 plague, locusts caused comparatively little economic damage as rain maintained lush green pastures well into the summer. During the 1984 plague, crop losses were limited to A$5.1 million due to an intensive locust control campaign that was estimated to give a net benefit of A$94 million or approximately 29 times the cost of control. An economic analysis of locust control by ABARE covering the period 2000-04 concluded net benefits of 8:1.
22. What strategy does the APLC use to minimise the development of locust plagues? Within the IPM framework (see FAQ 21), the APLC uses the strategy of preventive control to limit the development of locust plagues. The aim of preventive control is to delay a potential plague by limiting population increase until normal dry conditions intervene. A significant part (1/3 - 2/3) of the locust population is controlled whenever bands and swarms are present. The aim of preventive control is not to control all of the locusts but to reduce the rate of increase until dry conditions return and populations decline. This has been successful in limiting most outbreaks of the three locust pest species in eastern Australia (Australian plague locust, spur-throated locust and migratory locust), but when rains are particularly widespread or continue for a long period, populations can still reach plague proportions as they did during the 1999/2000 season.
23. Are the insecticides used to control locusts harmful to the environment? The insecticides used for controlling locusts are toxins and must be handled carefully. There is no evidence that APLC control operations have had any major or long-term impact on the environment. The APLC operates in an environmentally responsible manner and is pro-active in conducting research to monitor any possible effects on non-target organisms. The APLC maintains a strict 1.5 kilometre buffer zone between a sprayed target and any sensitive areas downwind. Research on the effect of fenitrothion on non-target grassland invertebrates showed that while the insecticide significantly reduced the density of some insect species immediately after spraying, populations recovered rapidly and there was no detectable effect on community structure. Currently, APLC environmental research is focussed at looking at the effect of locust control agents on vertebrates (birds, mammals and reptiles) and invertebrates (ants, springtails and termites). For further details see APLC Environmental Research.
24. Do the insecticides used by the APLC persist in the environment or pose a residue risk to stock or grain? If used correctly, as is ensured by APLC operating procedures, these risks are very low. The APLC applies very low doses of insecticide that degrade rapidly in the environment. To safeguard against the risk of insecticide residues in grain or stock in areas where locust control agents have been applied, strict withholding periods and/or slaughter intervals of 1 to 2 weeks are imposed. This allows ample time for the insecticides to break down to undetectable levels. For further information about withholding periods for locust control agents see the SAFEMEAT brochure on Locust control agents and livestock residues.
25. Why doesn't the APLC use a more natural method of control than chemical pesticides? The APLC uses a naturally occurring fungus called Metarhizium. Developed in collaboration with CSIRO Entomology, it was used operationally for the first time in the spring 2000 locust outbreak. Metarhizium is sprayed onto locusts (usually when they are in the hopper or nymph stage) as spores suspended in a mineral or vegetable oil using normal aerial spraying equipment. The fungus takes at least one week to kill the hoppers and is therefore not recommended for crop protection. At the moment, Metarhizium is more expensive than conventional insecticides and is being reserved for situations where insecticides cannot be used to control locusts (such as certified organic pastoral properties or environmentally sensitive areas). For further details see APLC Metarhizium.
26. When there is a locust plague, why doesn't the APLC catch them and use them as animal feed? Many people have suggested ways of catching large numbers of locusts such as using giant fluorescent lights mounted on trucks or giant vacuum cleaners. Unfortunately, none of the methods suggested so far would ever be economical, practical or as effective at controlling locust populations as aerial spraying currently is. When a locust outbreak occurs it is essential to control the infestation as quickly as possible (to restrict migration into agricultural areas) and in the most cost-effective way.27. How far can a locust travel in a single day? Locusts can travel over large distances during the night by being carried on strong warm winds associated with fronts or low pressure weather systems. Locusts that have enough fat reserves for migration take-off at sunset if the temperature is above 20oC flying to several hundred metres altitude and are carried by upper level winds. The locusts may move up to 500 kilometres or more in a single night, depending on wind speed and the number of hours they stay aloft. If no green vegetation is encountered after migration they will continue to move whenever weather conditions are suitable or until their fat reserves are depleted. Shorter distances (rarely exceeding more than 20 km per day) can also be covered by day-time flights. Not all long distance migrations are successful and during plague years large numbers of locusts have been found washed-up along the beaches of southern Australia or stranded in the middle of dry salt lakes.
28. How many eggs does a female locust produce? Locusts lay their eggs in the soil in pods at a depth of about 10 centimetres (picture). The female bores a hole in the ground with the tip of her abdomen, deposits 30-50 eggs and fills the remainder of the hole with a froth plug. This froth plug provides an escape route to the surface for nymphs when they hatch. Females can potentially lay up to 4 egg pods, at 5-7 day intervals under ideal conditions but few survive to lay a third time.
29. How long does it take for locusts to complete a generation? The life cycle of a locust comprises three stages: egg, nymph and adult (picture). When it is warm and the soil is moist, eggs hatch in 2-3 weeks. If conditions are dry or cool, development of eggs is delayed. Eggs of the Australian plague locust can remain dormant for many months. The nymphs or hoppers develop in five to six stages (instars) and when conditions are ideal they take about 25-30 days to reach the adult stage. Adult Australian plague locusts and migratory locusts take about two weeks to become sexually mature. They can live for several months and lay up to three or four times. Under ideal conditions these species can complete a generation in 6-8 weeks and have up to three or four generations per year depending on rainfall. In contrast, the spur-throated locust only has one generation per year as the adults of this species remain sexually immature during the winter dry season. For more details on the biology and life-cycle of locusts see the About Locusts section.
30. What species of locusts are important in other parts of the world? The most famous species of locust in the world is the Desert locust (Schistocerca gregaria). Plagues of this species were documented by the ancient Egyptians and it is this species that is referred to in the Bible. The Desert locust breeds in the semi-arid and arid deserts of Africa, the Near East and South-West Asia. It is considered to be the most important species of locust in the world as it has the potential to affect the livelihood of a tenth of the world's population during a major plague. For more information see the FAO Desert Locust Information Service website. There are several other important species of locusts throughout the world including:
- African migratory locust (Locusta migratoria migratoriodes) in Africa;
- Oriental migratory locust (Locusta migratoria manilensis) in south-east Asia;
- Red locust (Nomadacris septemfasciata) in eastern Africa;
- Brown locust (Locustana pardalina) in southern Africa;
- Moroccan locust (Dociostaurus maroccanus) in north-west Africa and Asia;
- Bombay locust (Nomadacris succincta) in south-west and south-east Asia;
- Tree locusts (Anacridium spp.) in Africa, Mediterranean and Near East;
- South American locust (Schistocera cancellata) in southern South America;
- Central American locust (Schistocera piceifrons) in Central America and northern South America
In North America, the Rocky Mountain locust (Melanoplus spretus) was a devastating pest across the USA during the late 1800s. This species mysteriously became extinct in the early 1900s. Today there are no true species of locusts that are pests in North America but there are many species of grasshoppers of major economic importance, in particular the migratory grasshopper (Melanoplus sanguinipes) - see the University of Wyoming grasshopper website for details. The Mormon cricket (Anabrus simplex), a type of katydid, can also be a serious pest in parts of the USA.
31. Do people eat locusts? People in several countries collect locusts for food particularly during outbreaks. Locusts are rich in protein and can be stir-fried, roasted or boiled. See the FAO Desert Locust Information Service FAQ's page for some delicious recipes.
If you have any questions about locusts that you would like answered send an e-mail to the Australian Plague Locust Commission