**Locusts** are a group of certain species of short-horned grasshoppers (family Acrididae) that have the ability to change their behavior, morphology, and color in response to high population density. This dramatic shift is known as **phase transition** (from solitary to gregarious). When gregarious, they form massive, dense, migratory **swarms** that consume virtually all vegetation in their path. Locusts are arguably the most historically devastating insect pest, causing catastrophic famine and agricultural destruction across Africa, the Middle East, and Asia.
Taxonomy and Classification
Locusts belong to the order Orthoptera. They undergo incomplete metamorphosis. The key species causing major outbreaks worldwide is the **Desert Locust** (*Schistocerca gregaria*). The change in phase is triggered by environmental conditions, particularly high rainfall followed by a period of crowding, which activates specific hormones related to serotonin, causing the insects to become social and migratory.
Physical Description
Adult Locusts are 1 to 3 inches long.
- **Solitary Phase (Key ID):** Cryptically colored (green or brown), isolated, and sedentary, behaving like a typical grasshopper.
- **Gregarious Phase (Key ID):** The body form changes (wings get longer, body color changes to bright yellow/pink/black), they become highly active, and their behavior shifts to strong mutual attraction, leading to the formation of massive, dense, coordinated swarms.
- **Damage Sign:** Complete and rapid **defoliation** of all crops and natural vegetation in the swarm’s path. Swarms can contain billions of individuals and cover hundreds of square miles.
Distribution and Habitat
Locusts are primarily pests in arid and semi-arid regions of the Old World (Africa, the Arabian Peninsula, and Southwest Asia). Their outbreak area (where they transition to gregarious phase) is the vast desert and semi-desert fringes that receive sporadic rainfall. Their swarms migrate hundreds of miles, crossing international borders.
Behavior and Conflict
The conflict is catastrophic, regional-scale food security risk.
- **Devastation:** A single small swarm can consume the amount of food necessary to feed thousands of people in one day.
- **Mobility:** Swarms move rapidly and can fly for hours, making their control a massive logistical challenge, especially in remote regions.
- **Rapid Reproduction:** Their ability to reproduce quickly following optimal rain events means populations can explode from insignificant numbers to massive swarm levels in weeks.
Management and Prevention
Control is global, cooperative effort focused on early detection and eradication of the pre-swarm stage.
- Monitoring teams constantly survey remote outbreak areas for small, dense bands of flightless nymphs (hoppers) or newly formed adult groups.
- When groups are found, they are aggressively treated with **insecticides** (usually Ultra-Low Volume aerial spraying) to kill the population before they become large, mobile swarms.
- **Biopesticides** (based on entomopathogenic fungi like *Metarhizium acridum*) are used, especially in ecologically sensitive areas, as they are specific to grasshoppers/locusts.
Conservation and Research
Locusts are managed as a global plague and a high-priority target for international agencies (FAO). Research focuses on understanding the molecular basis of the phase shift, improving satellite monitoring for green vegetation in outbreak areas, and developing more environmentally friendly biopesticides.