Explainer: Locust Swarms & their history in India
Sai Krishna Muthyanolla
June 2, 2020
Locust swarms were seen to have emerged in many places of Rajasthan & Uttar Pradesh. But what are these locust swarms? Have they caused damage earlier in India? Here is a detailed explainer.
Over the past few days there are reports of emergence of swarms of locusts in India, especially in different places of Rajasthan, Uttar Pradesh, with possible spread to Gujarat and other states.
With the country already reeling due to the impact of COVID-19 and the lockdown, the potential damage that can be caused by locust swarms has added to the apprehension and panic among public.
However, the emergence of locust swarms is not a new phenomenon and India has a history of regular occurrence of the locusts. In this story we take a look at the type of locusts, their emergence and distribution, economic impact and other details relating to the locusts.
Desert Locust is one of the four species found in India
The locust swarms that are currently being reported in India belong to the species of Desert Locust (Scientific Name: Schistocerca gregaria). Locusts are short-horned grasshoppers whose behaviour includes :
In certain circumstances, the locusts are capable of forming swarms i.e. congregation of adults as well as hopper bands (congregation of nymphs/immature insects). This ability to form large swarms and migrate at rapid rates over large areas along with their gregarious feeding habit makes them a threat to crops and other vegetation.
There are 10 important species of locusts, whose details are below.
Out of these, four species are found in India – Desert Locust, Migratory Locust, Bombay Locust & Tree Locust.
Desert locusts in gregarious condition form Swarms.
As highlighted earlier, locusts are a type of grasshoppers. The life cycle of Locusts consists of three stages : (1) Eggs (2) Hopper (3) Adult.
The eggs are laid in pods in moist sandy soil at a depth of 10 cm. The rate of development of eggs depends on soil moisture and temperature. The incubation period is 10-12 days with an optimum temperature between 32-35 °C. No development of egg takes place below 15°C.
In most cases, these grasshoppers are solitary creatures. However, certain circumstances like scarcity of food or drought conditions drive them to form groups.
Once the population of the group increases, they tend to become gregarious i.e. tendency to form large groups to hunt or eat together.  As per experts, Locusts tend to become gregarious when they constantly touch each other on the hind legs and release a chemical called serotonin.
These gregarious locusts start co-ordinating their movements and form swarms.
There are three forms of swarms identified :
There are marked changes observed in the locusts in terms of their behaviour as well as their appearance, once they enter this gregarious phase.
As per UN’s Food and Agriculture Organization (FAO), locusts have the ability to multiply nearly 20-fold in span of 3 months when the conditions become favourable, like good rains.
In general, there are three breeding seasons for locusts:
India has only one breeding season i.e. Summer breeding, meanwhile Pakistan has both spring and summer.
Desert Locusts are transboundary pests ranging from Northwest Africa to Indian Subcontinent
As per government information, parts of around 64 countries come under the area covered by desert locusts i.e. around 30 million sq. kms. The Geographical extent includes:
They inhabit a broad range belt of Arid and Semi-arid region from Atlantic Ocean to North West India, during their quiet period.
The Scheduled Desert Area in India encompasses 16 districts across the states of Rajasthan, Gujarat and Haryana. This covers a total area of around 2.05 lakh sq. kms.
Current Locust Swarming has its origins in East Africa
The size of the locust swarms being seen in India currently are larger compared to recent years. The locusts generally arrive in India during their Summer breeding season i.e. July-October.  The current swarm of locusts entering India is attributed to the spate of heavy cyclones and rainfall over the past two years due to  climate change.
The arid regions of Arabian Peninsula and East Africa are among the typical regions where the desert locusts reside. The Horn of Africa region experienced heavy rains in 2018, which followed a phase of severe drought in previous years. This resulted in severe floods in countries like Kenya, Somalia and Ethiopia. The resultant wet climate created conditions favourable for breeding of the locust. Even the hitherto, dormant eggs were re-awakened, and this has resulted in near 8,000-fold increase in the locust numbers and reaching swarm levels by early 2019.
These then moved to Iran, Yemen, Saudi Arabia and into Pakistan. Here, newer swarms were formed. Eventually they landed in India. The unexpected rainfall during November 2019 in Thar desert has created favourable conditions for breeding of locusts. As per FAO’s bulletin, the spring breeding is continuing in Iran and Pakistan. The availability of less vegetation due to summer in these countries has resulted in the swarms moving out from these areas and enter their breeding areas along Indo-Pakistan borders.
The strong westerly winds from Cyclone Amphan has driven the swarm further east.
Last upsurge of locust swarms was observed in 1997
India has a history of locust plagues and upsurges. The most recent significant upsurge was in 1997, where in there was incursion of 4 swarms. The number of recorded swarm incursions has varied earlier. The highest upsurge was observed in 1993, where in there were 172 swarms.
Post 1997, there have only been small and isolated instances of locust swarms until 2010, with relatively silent periods in the ensuing years.
Prior to 1962, there have been multiple instances of Locust Plague inflicted on India. This used to occur in phases of plague cycles i.e. a period of more than two years of wide-spread breeding, swarm production and damage of crops (Plague Period) followed by a period of 1-8 years of very little locust activity (recession), again followed by Plague period.
Since 1812, there have been multiple Plague periods observed. The last recorded plague cycle was during 1959-62 post which there have been instances of only Locust upsurges as indicated earlier.
Economic Loss due to Locust swarms
One of the major effects of a locust invasion is the economic loss, especially due to the damage caused by them to crops.
For the current year, the harvest for Rabi season is already completed, therefore the country has escaped from any major potential loss which could have occurred due the current locust swarming. Over the previous years as well, the conclusion of Rabi season prior to the Summer breeding season of locusts has helped the country from incurring major crop losses.
The locust swarms used to subside mostly by the Kharif season there by keeping the losses a minimum. However, with the potential size of the swarms increasing and favourable weather encouraging the breeding, it is yet to be seen if there would be any impact on the Kharif season.
Locust Warning Organization plays a key role in identifying & controlling locust invasion
The impact and damage of locusts swarming has gradually reduced over the years. As highlighted in this story earlier, there has been no instance of Locust plague since 1962 and no major locust upsurge was recorded since 1997. This success can be majorly attributed to the efforts put in by Locust Warning Organization (LWO) under the Ministry of Agriculture.
The origins of this organization can be traced back to the British Era, where in concerted efforts were made during 1930s to address the challenge posed by Locust invasions. This led to the establishment of Central Locust Bureau on 1930, a precursor to Locus Warning Organization, established in 1939.
In 1946, this was amalgamated into Directorate of Plant Protection Quarantine and Storage (PPQS) of Ministry of Agriculture. The Central Headquarters of LWO is located in Faridabad. Its Field headquarters, which handles the technical aspects and mentoring is located in Jodhpur, Rajasthan.  It has 10 Circle offices in different locations.
The main objective of LWO is to protect the standing crops and other vegetation from the damage caused by Desert Locusts.
The LWO performs various functions in line with these objectives.
The LWO runs its operation in line with the guidelines of Food & Agriculture Organization (FAO).  The fortnightly bulletin published by LWO is key to understanding the current situation relating to locusts.  Latest Locust Bulletin is issued for the period 1 -15 May, 2020.
Government takes cognizance of the Locust situation in India
Recent news reports suggest a wider spread over the last fortnight. As per a press release by Ministry of Agriculture on 27May 2020, the government confirmed that locust swarms have swept over North India and responsive action is initiated in affected areas in Rajasthan, Punjab, Gujarat and Madhya Pradesh.
It also stated that :
The press release also highlights the effort put in previous year i.e. 2019-20 in controlling the massive locust attack.
On 28 May 2020, the Union Agriculture Minister conducted a high-level meeting to review the Locust Control Operations. As per a press release made after the meeting,
Featured Image: History of Locust Swarms in India