Locust infestation fallout of climate change?
Arunima Sen Gupta
The swarm that is currently attacking India and other nations has its roots in heavy cyclones and rainfall over the past two years, a trend that has been attributed to climate change. Favourable conditions have been present for the growth of locusts since the beginning of this year. Having arrived in India through Iran and Pakistan, the desert locusts have not just registered their presence in the border states of Rajasthan and Gujarat, but in the interiors of Maharashtra, Uttar Pradesh and Madhya Pradesh as well. The UN Food & Agriculture Organisation (FAO) has associated much of their movements to strong westerly winds from Cyclone Amphan in the Bay of Bengal. The large scale breeding is a consequence of unusual rainfall which turned into many hoppers and immature adult groups. As the cyclon Amphan hit the shores, it caused changes in the wind, drawing the swarms of locusts into the central parts of the country. Therefore, main reasons behind the locust infestation can be attributed to the unseasonal heavy rains during their breeding season and strong westerly winds. Another aspect is that the swarms are full of immature locusts which feed on the vegetations voraciously. These insects can eat equivalent to their own weight, that too on fresh food. Also, the corona-led lockdown of the world aided their growth and movement.
What makes locusts swarm?
Locusts are grasshoppers, different from their peers in their ability to change behaviour, habits and migrate over large distances. Grasshoppers, or hoppers, are solitary creatures that don’t live in groups. But if driven by hunger caused by drought or food scarcity, they start to gather together while foraging for food. As their population increases in an area, they start becoming “gregarious”. In ecology, gregariousness is the tendency of animals to form social groups to hunt or eat together. It tends to induce hoppers to start coordinating their movements and form swarms. Gregarious hoppers are referred to as locusts. There are three forms of swarms: Small pockets confined to certain areas, called outbreaks; slightly larger groups, called an upsurge, that are still geographically confined; and mega groups, called plagues, of locusts that are separated by breeding locations but gather together in swarms. Locusts are believed to become gregarious when they constantly touch each other on their hind legs. The touching and tickling of hind legs release a large amount of serotonin, a ‘happy hormone’ also found in humans and released in the body during exercise. Experiments have shown that this can occur in as few as 10 locusts if they are tightly packed. The process of gregariousness also induces changes in appearance, turning them from green to a shade of yellow-brown, and strengthening their muscles. When locusts swarm, they adopt aligned movement and fly or march together. Nymphs, which are the flightless young of the locusts, march, and fly when their wings sprout. Desert locusts can fly over 130 km a day, and stay in the air for a long time. An FAO explainer states they have been known to cross the Red Sea, a distance of 300 km. A swarm is said to have flown a distance of over 5,000 km, from West Africa to the Caribbean, in 10 days in 1988. There can be as many as 40 million to 80 million locusts in a 1 square kilometre swarm. Female locusts can lay eggs at least thrice in their lifetime (roughly three to five months), at intervals of 6-11 days. Populations are said to have the capacity to multiply up to 20-fold in three months.
Not a new enemy
The swarms that have been attacking India in the recent past are unique in their strength and nature, but India frequently battles desert locust onslaughts. They usually arrive in July-October. India has not witnessed any full-blown locust cycle since 1962, except for a few surges in 1978 and 1993. In the 2019-20 cropping season, around 3.75 lakh hectares of crops were devoured by locust attacks in India with a loss of over Rs 100 crore, Ministry of Agriculture estimates suggest. Locusts have destroyed over 2 lakh hectares of crops in India since the beginning of May, and threaten another 6 lakh hectares of crop, an agriculture ministry official informed on condition of anonymity. Experts attribute the current deep invasion of locusts to the fact that while Rabi crops have been harvested, kharif sowing is yet to begin. The low availability of crops is leading the swarms to devour leaves on trees, and vegetable, fruit and cotton crops, and move deeper into India in search of fodder.
Where do they breed?
The desert locust typically lives in the Arabian Peninsula, in the arid regions of east Africa. Heavy rains in 2018 in the Horn of Africa region led many countries like Kenya, Somalia, and Ethiopia to flood, right after a very severe drought the previous year. For the locusts in the region, the wet conditions proved favourable. With even dormant eggs “reawakened”, they bred through three generations, leading to an 8,000-fold increase in locust numbers. By early 2019, the locust population in Africa had already reached swarm levels. From Africa, they moved to Iran, Yemen, and Saudi Arabia. Newer swarms formed and spread to Pakistan, where they devastated the cotton economy. The FAO said in January that the ongoing locust outbreak “is the worst to strike Ethiopia and Somalia for 25 years and the worst infestation that Kenya had experienced in 70 years”. They even flew back to Africa in the spring of 2019. Finally, this year, they landed in Rajasthan, swiftly moving into the country within a week. In 2019, the Thar Desert received unexpected rainfall that proved favourable for locusts to breed. According to the latest locust watch bulletin from the FAO, spring breeding continues in Iran and Pakistan where control operations are in progress. As vegetation dries out because of the summer season, more swarms will move from these areas to the summer breeding areas along both sides of the Indo-Pakistan border in several waves until at least early July.
Why do locusts ‘migrate’?
After the eggs hatch, they need to feed on green vegetation for growth and turn into an adult moth from nymph. Since deserts do not provide leafy cover, they venture out to the plains so that the large locust population can grow.
Are locusts dangerous?
These crop-devouring insects are not dangerous when they are roaming alone or in a small isolated group. It becomes a problem when they grow in a huge number. In such scenarios, there is a behavioural change and some transformation into forming swarms. A single swarm can include up to 40-80 million adults that too in one square km. Also, swarm size this big has the ability to travel up to 150 km in a day. This usually happens when conditions are favorable to them- a desert area and some vegetation nearby.
History of damage
Locusts have been known throughout history. They’ve been recorded in ancient Egypt through depictions on tombs dating back to 2500 BCE. The Bible records swarms from 1450 BCE. They’re also mentioned in the Quran and several other holy books. They’ve been recorded in ancient China, Greece, Rome, Syria, and other parts of the world. More recently, in the 19th century, a species of hopper known as the Rocky Mountain locust, now extinct, devastated large parts of the US. In 1875, a giant swarm reportedly consisting of over 12 trillion insects, spanning an estimated area of 5.1 lakh sq km — that is, bigger than Maharashtra and Karnataka put together — blacked out the sky over multiple states, like Colorado and Nebraska. They ate everything green, and more, including wool off sheep’s backs, harnesses off horses’ backs, and even the clothes people were wearing. This swarm was the largest gathering of any animal ever recorded. To curb the damage, desperate governments started introducing bounties for killed locusts, and farmers dug up pits and burnt them with flamethrowers. People even resorted to eating them. Grasshoppers and locusts are said to be among the most nutritious edible insects, with thrice the amount of protein than other kinds of meat. They’re a delicacy in many parts of the world, although this is changing with increased pesticide use. The Rocky Mountain locust population slowly started dwindling with changing farming activity. Ploughing, irrigation and mining are thought to have killed thousands of nests of eggs in the soil, bringing down their numbers. Within 20 years, this species disappeared off the face of the earth. The Rocky Mountain locust was last seen in 1902 and is now extinct. Its extinction is considered to be one of the biggest ecological mysteries. Today, North America and Antarctica are the only continents in the world to not have locusts.
India has ways to mitigate trouble
However, humans have a distinct advantage in fighting locusts now as compared to their ancestors — deeper knowledge and technology. Farmers have switched to crops that can be harvested much before swarming season, and the locusts themselves can be controlled and killed with pesticides. Monitoring for locust breeding is essential as it is much easier to destroy eggs than fully grown locusts. At present, the primary method of controlling desert locust swarms is through organophosphate chemicals (the prime ingredient in herbicide and pesticide) applied in small concentrated doses by vehicle-mounted and aerial sprayers along with knapsack- and hand-held sprayers. In rural areas of India, farmers have been known to beat steel utensils during late afternoons and evenings, and play loud music at night and create wood-fire, to ward off locust swarms from farms, albeit temporarily. Additionally, newer technology in the form of serotonin inhibition has shown promise in laboratory settings. As the current locust swarms attacking crops in India have bred and matured in Iran and Pakistan, New Delhi has offered assistance to both the countries to jointly combat the locust menace. However, only Iran has accepted the offer so far. The External Affairs Ministry has approached state-owned HIL for the manufacture and supply of the pesticide Malathion Technical to Iran. India also has a locust warning and control organisation (LWO), formed in 1939 and overseen by the Indian Council of Agricultural Research. The LWO monitors locust scenarios over desert areas. It has two headquarters, one in Faridabad (near New Delhi) for administrative duties and one in Jodhpur (Rajasthan) for technical operations. Strident efforts are underway to control the current ‘plague’. But how the swarms are finally arrested remains to be seen.
Facts about locusts you didn’t know
A desert locust lives a total of about three to five months. This is variable and depends mostly on weather and ecological conditions. The life cycle of a desert locust comprises of three stages - egg, hopper, and adult. Eggs hatch in about two weeks (the range is 10-65 days), hoppers develop in five to six stages over a period of about 30-40 days, and adults mature in about three weeks to nine months but more frequently from two to four months. A female desert locust lays eggs in an egg pod primarily in sandy soils at a depth of 10-15 centimeters below the surface. A solitary female lays about 95-158 eggs whereas a gregarious female usually lays less than 80 eggs in an egg pod. Females can lay at least three times in their lifetime usually at intervals of about 6-11 days. Up to 1,000 egg pods have been found in one square meter. Desert locusts usually fly with the wind at a speed of about 16-19 km/h depending on the wind. Locust swarms can travel about 5-130 kilometers or more in a day. They can stay in their air for long periods of time. Example: (a) Locusts regularly cross the Red Sea, a distance of 300 kilometers. (b) Travelled from North-West Africa to the British Isles in 1954 (c) Travelled from West Africa to the Caribbean, a distance of 5000 km in about 10 days in 1988A solitary desert locust usually flies at night whereas gregarious adults (swarms) fly during the day. Locust swarms can vary from less than one square kilometre to several hundred square kilometers. There can be at least 40 million and sometimes as many as 80 million locust adults in each square kilometre of swarm. A Desert Locust adult can consume roughly its own weight in fresh food per day that is about two grams every day. A 1 km2 size swarm contains about 40 million locusts, which eat the same amount of food in one day as about 35,000 people. This is based on a person eating an average of 2.3 kg of food per day. A swarm the size of Niamey (Niger) or Bamako (Mali) eats the same amount of food in one day as half the respective country. A swarm the size of Paris eats the same amount of food in one day as half the population of France; the size of New York City eats in one day the same as everyone in New York and California; the size of Rome eats the same of everyone in Kenya; the size of Sydney (Australia) eats the same amount of food in one day as Australia eats in 1.5 hours. Locusts do not attack people or animals. There is no evidence that suggests that locusts carry diseases that could harm humans. People in several countries collect locusts using large nets, or by other means. Locusts are usually stir-fried, roasted or boiled and eaten immediately or dried and eaten. 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.