A “plague of frogs” describes an ecological event where a frog population experiences an unsustainable and massive boom, exceeding the environment’s natural carrying capacity. While amphibians are a foundational part of healthy ecosystems, integrating aquatic and terrestrial food webs, an overpopulation creates an extreme imbalance. This overabundance stresses the local habitat and resources, fundamentally changing the ecosystem’s structure. The sheer biomass of frogs and their larvae can trigger a series of negative effects, impacting everything from insect populations to the transmission of deadly pathogens.
Severe Depletion of Local Insect Populations
The most immediate ecological damage from a frog plague is the hyper-predation of local invertebrate communities. Adult frogs are generalist predators with high metabolic demands, consuming vast quantities of insects, spiders, and other arthropods. This intense predation pressure rapidly depletes the local insect biomass, leading to a profound trophic cascade throughout the ecosystem.
The decline in insect populations includes both pests and beneficial species, such as pollinators. When frogs consume arthropod predators, a phenomenon known as intraguild predation occurs, which can lead to an unexpected rise in crop pests because their natural enemies have been suppressed. The loss of insect diversity and abundance also creates a resource bottleneck for other insectivores, including shrews, bats, and nesting birds, forcing them to compete with the overwhelming frog population. This competition reduces the reproductive success and survival rates of these insect-dependent vertebrates, further destabilizing the food web.
Habitat Stress and Resource Competition
A frog plague places immense physical and chemical stress on the shared aquatic and terrestrial environments. The high concentration of frogs and their tadpoles leads to intense competition not just for food, but also for resources like shelter, clean water, and breeding sites. Larval amphibians exist in such high densities that they significantly alter the water chemistry and plant life in their breeding ponds and streams.
Dense tadpole populations can dramatically reduce the abundance and biomass of aquatic macrophytes (water plants) through intense grazing. The continuous activity of numerous tadpoles also transfers nutrients from the bottom sediments into the water column, altering the balance of nitrogen and phosphorus. This nutrient shift stimulates the growth of certain types of algae, leading to changes in water quality and oxygen levels that stress other aquatic life, such as fish and aquatic invertebrates. On land, the sheer number of adult frogs competing for limited terrestrial refuges can displace other small vertebrates, including salamanders, turtles, and small mammals that rely on the same physical habitat.
Rapid Spread of Pathogens and Disease
High population density is the greatest accelerator for the transmission and virulence of infectious pathogens within a wildlife community. A frog plague creates ideal conditions for turning the environment into a massive disease reservoir, primarily for fungal diseases like chytridiomycosis. This lethal skin infection is caused by the fungus Batrachochytrium dendrobatidis (Bd), which thrives in dense amphibian populations.
In an overcrowded habitat, the fungal pathogen is rapidly spread through direct contact and the aquatic environment, where the motile infectious spores, called zoospores, are shed. The high density of hosts allows for an accelerated transmission rate, quickly increasing the infection intensity on individual frogs until it reaches a lethal threshold. This density-dependent transmission means that the infection prevalence can quickly reach 100% within a localized population. The massive frog population acts as a “super-spreader” event, increasing the environmental load of zoospores in the water, which poses a higher risk to other, more sensitive amphibian species.
The Cycle of Ecological Instability
The ecological consequence of a frog plague is a boom-and-bust cycle that prevents the ecosystem from maintaining long-term balance. The initial population boom is followed by an inevitable crash once the high density leads to widespread resource depletion and pathogen amplification. This rapid fluctuation from extreme abundance to near-absence is far more damaging to ecological resilience than a stable, moderate population would be.
The bust phase, triggered by mass starvation and disease mortality, leaves the ecosystem severely damaged. Insect populations are decimated, the aquatic habitat is chemically and physically altered, and the entire amphibian community is weakened by disease exposure. The subsequent crash removes a significant food source for secondary predators, such as snakes and wading birds, which suffer population declines in response. The ecosystem is left in a state of reduced biodiversity and lowered functional capacity, vulnerable to further disturbance.