Minnesota is home to a diverse population of native amphibians, but none are dangerously poisonous. Highly toxic species, such as the vibrant poison dart frogs, are only native to tropical regions like Central and South America. While some Minnesota amphibians secrete defensive toxins, these substances pose no serious threat to humans and are considered mild irritants. Understanding the distinctions in how animals use toxins offers a clearer perspective on the local ecosystem.
Defining Toxicity in Amphibians
Defining Poisonous vs. Venomous
The term “poisonous” is distinct from “venomous,” referring to how a toxin is delivered. A venomous animal, such as a rattlesnake, injects its toxin actively through a bite or sting. In contrast, a poisonous animal delivers its toxin passively, meaning the poison must be ingested or absorbed through the skin. Amphibians are generally considered poisonous because they secrete defensive compounds from glands in their skin to deter predators.
Minnesota’s Defensive Secretions
The American Toad, native to Minnesota, produces a milky substance called bufotoxin from glands located behind its eyes. This chemical defense tastes bitter and is highly irritating to the mouth and throat of a predator. While bufotoxin is not lethal to humans, the compounds can cause salivation, discomfort, and vomiting in pets that mouth or ingest them. The Pickerel Frog also secretes a mild toxic irritant that makes it unpalatable to many predators, but the risk to humans is minimal.
Common Amphibians of Minnesota
The majority of frogs and toads found across Minnesota are entirely harmless. Commonly encountered species include the Northern Leopard Frog, the Wood Frog, and the Spring Peeper. These species rely on camouflage and agility to evade detection, not chemical defenses. The Green Frog and the Boreal Chorus Frog are also widespread, inhabiting various aquatic environments from ponds to marshes. These true frogs and small tree frogs do not secrete the bufotoxins associated with toads.
Practical Safety and Handling
Despite the low toxicity risk, general hygiene practices are recommended when interacting with any wild amphibian. Amphibians can be carriers of zoonotic bacteria, most notably Salmonella. These bacteria live naturally on the skin and in the digestive tract of frogs and toads. Transmission to humans occurs primarily through hand-to-mouth contact after handling an animal. To prevent illness, washing hands thoroughly with soap and water immediately after touching any frog or toad is the most effective safety measure.
Pet owners should supervise dogs and cats, as they are likely to mouth an American Toad and suffer from the irritating effects of bufotoxin. If a pet contacts a toad and begins foaming or pawing at its face, immediately flush the mouth with a hose. Point the water forward to avoid swallowing, which helps remove the toxin.