Migratory Locust (Locusta migratoria)

Description

The migratory locust displays polyphenism, having two phases, solitary and gregarious. The size and color vary according to their stages. The color of the solitary locusts varies from brown to green with the intensity of the green varying as per the color of the foliage they thrive in.

In the gregarious phase, which they may reach at any point in their lives, the locusts appear brownish with tinges of yellow. In fact, the yellow coloration becomes more intense with maturation. Some gregarious locusts also have a bluish body and yellow head and legs.

These heavily built locusts have a blocky stature. There is a central ridge running past the thorax, more prominent during the solitary phase. However, during the gregarious phase, the ridge becomes lost partially. The dark forewings have thin and light marking, while, the hindwings are either clear or marked with a faint shade of smoky blue or green.

The gregarious adults vary in size according to the sexes, the females appearing larger, at 40-65 mm, than their male counterparts, who measure 35 – 45 mm. However, the solitary locusts are bigger.

Distribution: Africa, Australia, New Zealand, Asia and Europe (once common but now rare)  

Habitat: Mainly grasslands

Do they bite: No

Lifespan: About two months  

Predator: Birds of prey

Behavior and Characteristics  

Social

The migratory locust goes transitions between the solitary and gregarious phase and vice versa, depending upon the population density.  A solitary locust becomes a gregarious locust when there is an increase in the density of population. When the population is less dense the reverse happens, the gregarious entering into a solitary phase.

The DNA methylation in the brain plays a significant role in influencing the transition between the solitary and gregarious phases. The Dnmt3 enzyme appears high in the gregarious locust’s brain, but decreases when they move to an isolated environment. Reversely, it is low in the solitary locust’s brain but increases when they become gregarious, swarming together.

Migratory

Like all other locust species, the migratory locust travels at 115-20 km ph. In fact swarms can travel between 5 and 130 km in one day. When in the gregarious phase, they migrate for long distances in a huge swarm. During their solitary phase, they migrate too, but most of it takes place at night.

Feeding

They commonly feed on crops, capable of eating the amount of food equivalent to its own weight each day. When millions of locusts have gathered together they would feed on food weighing one ton.

Life Cycle

1. Egg Stage

The eggs are mostly laid by the females after rains. However, their eggs barely survive when the temperatures are dry. There are around 50-60 eggs in a single egg pod. A females lays around 3-5 egg pod in her lifetime. The eggs develop in around 11-15 days, the temperature playing an important in their maturation.

2. Nymph Stage

Under normal temperature, the nymphs hatch from the eggs in around 30 days, going through 5-6 molts before reaching the adult phase. The presence of a congregation of nymphs makes them gregarious, displaying a marching movement. Bands of locusts can partake a journey of 500 m per day that however, depends on the condition of the surrounding vegetation.

The color pattern of the larvae also differs according to their phase. The gregarious larvae are yellow or orange with black spots, while the solitary larvae have a green or brown body.

3. Adult Stage

They reach sexual maturity in fourteen days from development, having a shirt lifespan though.

Impact on Humans

The African migratory locust caused severe damage in Africa between 1928 and 1942. Since then several conservation methods have been adopted to keep a check on their increasing population. The Malagasy migratory locust known to swarm at least two times in a ten year span is even considered a threat. These locusts are edible, with the European Food Safety Agency approving the dried, frozen, and grounded form of this insect safe for human consumption.