A group of shrimp is called a swarm, a term shared with many other small, densely packed marine and insect species. Shrimp are found in oceans, rivers, and lakes worldwide, and many species gather in large, tightly clustered groups, particularly around food-rich areas like coral reefs, seagrass beds, or nutrient-heavy currents.
Swarming behavior offers shrimp real survival advantages. Moving in large numbers makes it statistically less likely for any individual shrimp to be picked off by a predator, and it can also help shrimp overwhelm feeding opportunities faster than they could alone. Some shrimp species take this further with mass synchronized migrations, moving together across the seafloor in long, snaking lines that can stretch for surprising distances.
Shrimp are also sometimes referred to by other collective nouns depending on species and context, including a troup or simply a school, but “swarm” captures the chaotic, high-density clustering that’s especially common among smaller shrimp species.