The coqui frog (Eleutherodactylus coqui), a small amphibian native to Puerto Rico, has become a significant invasive species in other regions, particularly Hawaii. While cherished in its homeland for its distinctive nighttime calls, its introduction to new environments has led to a range of ecological and economic challenges. Its adaptability and rapid reproduction allow it to establish dense populations, disrupting local ecosystems.
The Multifaceted Impacts
Coqui frogs create several problems in invaded areas, with noise pollution being immediate and noticeable. The male coqui’s loud “co-qui” call can reach 80 to 100 decibels at 0.5 meters, comparable to a running lawnmower or a table saw. This persistent vocalization, from dusk until dawn, disrupts human sleep, diminishes quality of life, and negatively affects property values. One study indicated a 0.16% loss per transaction within 500 meters of a frog complaint.
Beyond acoustic disruption, coqui frogs cause considerable ecological imbalances. They are nocturnal, generalist predators that consume a wide variety of native insects, spiders, and other invertebrates. Their high population densities, sometimes exceeding 90,000 frogs per hectare in Hawaii, can lead to substantial declines in native invertebrate populations by consuming hundreds of thousands of invertebrates nightly. This intense predation can alter the food web and impact nutrient cycling in forest ecosystems.
Economic consequences extend to various sectors. The decline in property values due to noise pollution is a direct financial burden on homeowners and affects real estate markets. The floriculture and nursery industries face significant challenges, including increased costs for pest control, quarantine procedures, and reduced sales, as frogs or their eggs hinder export. Control efforts also incur substantial costs for government agencies and private landowners. The perceived decline in environmental quality due to pervasive noise and altered ecosystems can negatively affect tourism.
From Native to Invasive: How They Spread
The coqui frog’s journey from its native Puerto Rico to become an invasive species, particularly in Hawaii, primarily occurred through accidental human-mediated transport. The main pathway of introduction has been through the movement of nursery plants, potted plants, and landscaping materials. These small frogs, often less than 2 inches long, can easily hide within vegetation and soil, hitchhiking unnoticed in shipments.
Once introduced, several biological factors contribute to their rapid establishment and spread. Unlike most frogs, coqui frogs do not have a tadpole stage, with eggs developing directly into small froglets. This direct development removes the need for standing water, allowing them to colonize a wider range of terrestrial habitats. They also have a rapid breeding cycle, with females laying clutches of 15 to 40 eggs approximately every eight weeks, allowing for quick population growth. In new environments like Hawaii, the absence of natural predators enables their numbers to explode, often reaching densities significantly higher than in their native range.
Controlling the Invasion
Managing coqui frog populations in invaded areas presents considerable challenges due to their high reproductive rates, nocturnal habits, and widespread distribution. Various methods are employed to control their numbers. Chemical control primarily relies on substances like citric acid, which is approved for use in Hawaii and is effective in killing frogs, eggs, and juveniles upon direct contact. A 16% citric acid solution is commonly used, applied to infested plants at night when frogs are active.
Non-chemical methods include habitat modification, which involves removing dense vegetation, leaf litter, and other moist hiding spots that coqui frogs prefer during the day. Manual removal and trapping, often using PVC pipe traps that exploit their nesting behavior, can also be effective for smaller, localized infestations. Hot water or steam treatments are used for plant shipments to kill frogs and eggs. While biological control research is ongoing, introducing new predators poses risks of unintended ecological consequences. Preventing further spread through vigilant inspection of plants and materials remains a primary strategy.