There have been recent news reports of billions of locusts swarming across regions of eastern Africa. We have had our grasshopper populations increasing in Manitoba over the last couple of years, but in perspective, our levels pale in comparison to what is happening in eastern Africa. The distinction between a locust and a grasshopper may not be clear to many. Are locusts the same as grasshoppers? Or is there something different that makes them behave differently than other grasshoppers. In this month’s Incredible Creatures we will explore the interesting world of locusts, look at the locust situation in eastern Africa, and examine whether locusts are, or have been, a potential threat in Canada.
Locust vs. Grasshopper: What’s the Difference
All locusts are grasshoppers, but not all grasshoppers are locusts; the term locust only applies to about a dozen species. There are lots of species of grasshoppers, including a group referred to as short-horned grasshoppers, of which there are 129 species in Canada, and more than 6,700 species worldwide. The term locust refers to certain species of short-horned grasshoppers that have a swarming phase. They are usually solitary (acting as individuals), but under certain circumstances they become more abundant and change their behaviour and habits, becoming gregarious (acting as a group). The appearance of the locust also changes. For example, solitary adults of the desert locust are brown whereas gregarious adults are pink (when younger) and yellow (when older). Until 1921, it was thought that the Desert Locust was actually two different species of locusts.
Normally these locusts occur at low levels, and they do not pose a major economic threat to agriculture. However, under suitable conditions of drought followed by rapid vegetation growth (such as can happen after heavy rains), numbers will rise. When it later becomes drier, and food gets less abundant, they will be forced closer together. They will then see, smell and touch each other more. This results in an increase in a chemical in the brain called serotonin (the same neurotransmitter that controls mood in humans) triggering a dramatic set of changes. They start to breed abundantly and become gregarious and nomadic (sometimes referred to as migratory) when their populations become dense enough. When they are young the wings are not developed and they form bands of flightless nymphs, which later become swarms of winged adults. Both the bands and the swarms move around and can rapidly strip fields and cause damage to crops. The adults are powerful fliers. They can travel great distances, consuming most of the green vegetation wherever the swarm settles. Researchers found that tickling locusts back legs for a couple of hours could induce the locusts to make more serotonin because they interpreted that stimulus as the jostling of other insects. In another interesting experiment, if locusts species of grasshoppers were given serotonin blockers, they stayed solitary even in swarm-inducing conditions.
We do not currently have any species of locusts in North America. There are several species that can be of great concern in other parts of the world though. The desert locust is one of the better-known species and occurs across North Africa, the Middle East, and the Indian subcontinent. But there are other species as well. Some of these, and the regions they occur in are the migratory locust (Africa and Southeast Asia), the red locust (Eastern Africa), the brown locust (Southern Africa), the Moroccan locust (Northwest Africa to Asia), the Bombay locust (Southwest to Southeast Asia), the Italian locust (from Western Europe to Central Asia), and Australia has the Australian plague locust.
Africa’s Current Locust Issues
There have been many news reports in recent weeks about billions of desert locusts, swarming across eastern Africa. These have mainly affected Kenya, Somalia, and Ethiopia but continue to spread. Some of the “Locust Watch” reports of the United Nations’ Food and Agriculture Organization (FAO) in late-February describe swarms moving from Kenya into Uganda. The swarms described in these news reports are massive; one of the largest in Kenya is about 60 kilometers long and 40 kilometers wide. Desert locusts consume an amount roughly equal to their body weight each day, which is about two grams. Each square kilometer of the swarm can include about 40 million locusts and eat as much food in one day as about 35,000 people (based on a person eating an average of 2.3 kg of food per day) according to the FAO. To manage the insects, Kenya and Ethiopia are spraying insecticides from airplanes. The countries have about five airplanes each, but as the locusts spread, there are more of them than the local systems can handle. Somalia has declared the swarms an emergency, but can’t deploy insecticide-spraying planes because of security concerns in the country, where some areas are controlled by the al-Qaida-linked group al-Shabab.
So what is the cause of these swarms? According to Keith Cressman, the FAO’s senior locust forecasting officer, the swarms are reaching such an unusual size now because of cyclones that rained on the deserts of Oman last year. In the past 10 years, there’s been an increase in the frequency of cyclones in the Indian Ocean. Eight cyclones occurred in 2019. “Normally there’s none, or maybe one. So this is very unusual,” Cressman says. He also states “if this trend of increased frequency of cyclones in the Indian Ocean continues, then certainly that’s going to translate to an increase in locust swarms in the Horn of Africa.”
The Rocky Mountain Locusts
You may have noticed that earlier in the article I mentioned “We do not currently have any species of locusts in Canada”, and you may have wondered what does he mean by currently. We used to have a species of locust known as the Rocky Mountain locust, but it went extinct.
The Rocky Mountain locust was formerly one of the most significant insect pests in North America before it became extinct. An entomologist from Manitoba, Norman Criddle, collected the last live specimens of the Rocky Mountain locust in 1902. In the 1930s, during the Dust Bowl, the second species of North American locust, the High Plains locust (Dissosteira longipennis) reached plague proportions in the American Midwest. Today, the High Plains locust is a rare species, leaving North America with no regularly swarming locusts.
The extinction of the Rocky Mountain locust has been a source of puzzlement. It had swarmed throughout the west of the United States and parts of Canada in the 19th century. There are several theories to attempt to explain extinction. One theory was that the ecology of the locust was somehow linked to the great herds of bison and that the extermination of the bison from most of its range brought about the extinction of the Rocky Mountain locust. These two major and competing grazers had coexisted on the plains for thousands of years, so it was proposed that the bison somehow altered the ecology of the grasslands to favor reproduction and survival of the locust. Another theory is that cattle grazing and homesteaders’ cultivation of the breeding grounds of the insect during a population recession of the locust in the 1880s may have irreversibly disrupted locust reproduction. This is the only instance of a major pest insect being eradicated.
Locusts as Food
If you can’t beat’em, eat’em. Reference to people eating locusts goes back a long way. The Bible records that John the Baptist ate locusts and wild honey while living in the wilderness. The Islamic prophet, Muhammad, was reported to have eaten locusts, and eating locusts is considered halal.
Locusts are considered a delicacy and eaten in many African, Middle Eastern, and Asian countries.
People in several countries collect locusts using large nets and by other means. Locusts are usually stir-fried, roasted or boiled and eaten immediately or dried and eaten later (the FAO website actually includes some locust recipes). Locusts are rich in protein. During periods of increased locust activity, piles of dead locusts can be found in the market places of many locust affected countries.
During the years of the Rocky Mountain locust in North America, Charles Riley, an entomologist from Missouri, came up with a recipe for locusts seasoned with salt and pepper and pan-fried in butter. The recipe sold, but some stated that they “would just as soon starve as eat those horrible creatures”. So not all were big fans to this approach of turning a crop pest into a meal.
With their change in appearance and ability to create massive swarms, locusts are not just your average grasshopper. It is a bit ironic though that the only major insect pest to go extinct was a type of locust.