The desert locust is a type of grasshopper that can change morphology and behavior under specific environmental conditions. Normally, grasshopper behavior is characterized by a preference for solitude and hopping around. When conditions are good and vegetation becomes more plentiful, locusts transform from loner hoppers to swarming menaces. These two different phases are referred to as solitarius and gregarious and are accompanied by a striking physical change. The image below shows an example of physical change in both the final larval instar developmental phase and in an adult desert locust.

Image courtesy of Burrows et al.

The cause of behavioral and morphological changes in locusts has been widely studied and is the quintessential biology textbook example of phenotypic plasticity or the ability for an organism to have more than one phenotype resulting from the same gene. A phenotype is an observable characteristic of an organism that results from genetic and environmental interactions. The desert locust phenotype changes from brown and solitary to yellow and swarming. Researchers have shown that the protein that is responsible for color change in one species of locust is beta carotene. They propose that this shift to a more striking color — bright yellow — serves as a signal to other locusts to assist swarming behavior.

Locusts go through this transformation due to an increased density of locusts. An increased presence of locusts in the surrounding area triggers the stimulation of a locusts’ legs, which causes a release of serotonin. This serotonin causes a cascade of changes to trigger the color change, higher daytime activity and increased attraction between locusts to group together. Densities of locusts increase when there are plentiful resources and they have consequently evolved to take advantage of those resources at the optimal time. The change in environment triggers a genetic regulation difference which manifests in morphology, behavior and group dynamics.

Once these animals alter their behavior and physiology to suit the environment, they eat everything in sight. This makes them excellent at exploiting good conditions. Just as farmers have a plentiful crop season due to moderate to heavy rain, the locusts come along and eat all the produce before harvesting time. This is proving to be devastating in Kenya, Ethiopia and Somalia, where food security is already a concern due to instability. The locusts go through different breeding cycles as they move to find more food –– increasing numbers threaten Uganda, Tanzania and South Sudan among the at least 20 countries the UN has qualified as being at risk. Hundreds to millions of locusts in a swarm can cover an area the size of Manhattan and can eat as much food as all of Kenya’s population in a single day.

In countries that are already struggling to provide food for their human populations, this pest is wreaking havoc on both the ecosystem and social systems. Local and international organizations like the UN are devoting increased attention to the impact that these swarms have on crop production in the region. People need food urgently and the UN has requested 76 million USD in aid to offset the effects of the unexpected invasion. 10 million people in the region are at risk of hunger directly caused by the locust invasions.

While much attention has been focused on food availability, the environmental impact of these locust swarms also needs careful monitoring. The locusts are eating all the vegetation in already arid regions which can spell disaster for local species that need these plants for food. Moreover, the main effort that is in place to contain the problem is large-scale pesticide sprays. The Ugandan government is responding to the swarms by enlisting its military to conduct pesticide spraying on the ground. The impact of these pesticides will undoubtedly have an impact on local insect species and community dynamics. Pesticides were famously targeted as the main cause for decreases in bird populations and ecological disruption in Rachel Carson’s 1962 book, Silent Spring. Since then, many pesticides have been banned from different countries due to their unintended effects on local flora and fauna. We will not know the effect of the heavy pesticide use in these countries until after the immediate threat to food security has passed.

This problem may seem like a whole ocean away, but is much closer to home than you think. Locusts usually thrive in the deserts of the Arabian Peninsula without becoming swarms. Unnaturally heavy rains due to climate change caused them to flourish this season and migrate from Yemen to mainland Africa, where cyclones in Somalia allowed the locusts to have yet another breeding season before spreading further. This is the worst locust season that most of East Africa has seen in 25 years and worse than the infamous season in Kenya 70 years ago. In February 2019, there were swarms of locusts that threatened Abu Dhabi’s crops. There have not been problems with locusts this year in the UAE, but perhaps this may be detrimental to some food availability because the locust is considered a Bedouin delicacy.

Despite the remarkable biology of the locust and its potential for foodstuffs, the insect endangers the security of millions of people.