Maryland is home to no brightly colored poison dart frogs, but it does harbor native amphibians that produce genuinely toxic skin secretions. The pickerel frog is the standout, widely considered the only truly poisonous frog native to eastern North America, and it lives in cool streams and wetlands throughout the state. Several toad species round out the picture, secreting potent chemicals from specialized glands that can sicken pets and deter predators. The story of toxic amphibians in Maryland is quieter and less dramatic than the neon-colored frogs of Central American rainforests, but it is real and worth understanding, especially if you have curious dogs or handle amphibians outdoors.
The Pickerel Frog, Maryland’s Only Toxic Frog
The pickerel frog (Lithobates palustris, still sometimes called Rana palustris in older literature) is found across Maryland in cool, clear streams, springs, and the wooded edges of ponds. It is a medium-sized frog, typically two to three inches long, with distinctive rows of roughly rectangular dark spots running down its back on a tan or light brown background. The underside of its hind legs shows a bright yellow or orange wash, a subtle warning flag that most people never notice.
What makes the pickerel frog unusual among eastern frogs is that its skin secretions are genuinely toxic. Researchers who have analyzed these secretions found they contain a complex cocktail of antimicrobial peptides, at least 22 distinct peptides with activity against bacteria and yeast. Some of these peptides, belonging to families called esculentins and palustrins, are potent enough to inhibit the growth of E. coli at very low concentrations.1PubMed. Multiple antimicrobial peptides and peptides related to bradykinin and neuromedin N isolated from skin secretions of the pickerel frog, Rana palustris Beyond fighting microbes, these secretions are noxious enough to kill or repel other frogs housed in the same container, which is something herpetologists learn the hard way when they accidentally mix pickerel frogs with other species during fieldwork.
For humans, the risk is minor but real. Handling a pickerel frog and then touching your eyes, mouth, or a cut can cause irritation and a burning sensation. The secretions are not life-threatening to people, but they are unpleasant enough that you will want to wash your hands after picking one up. If you spend time flipping rocks along Maryland streams looking for salamanders or crayfish, the pickerel frog is the one amphibian you should handle with a bit of respect.
Toads in Maryland and Their Parotoid Gland Toxins
While the pickerel frog is Maryland’s only truly toxic frog, the state’s toads carry their own chemical arsenal. Two species are common across the state: the American toad (Anaxyrus americanus), found in forests, gardens, and suburban yards statewide, and Fowler’s toad (Anaxyrus fowleri), which prefers sandier soils and is more common on the coastal plain and along river valleys. Both belong to the family Bufonidae, the “true toads,” and both produce toxins.
The primary weapons are the parotoid glands, the large swollen bumps located just behind each eye. These glands, along with smaller granular glands scattered across the skin, secrete a mix of chemicals that can include cardiac glycosides like bufadienolides, alkaloids, and biogenic amines such as bufotenine.2Oxford Academic. Transcriptomic Analysis Reveals Potential Candidate Pathways and Genes Involved in Toxin Biosynthesis in True Toads Unlike tropical poison frogs that acquire their toxins from their diet, true toads synthesize these chemicals themselves, which means a toad raised in captivity on a bland diet of crickets is still toxic.
The effects on predators range from unpleasant to lethal. At the mild end, any animal that mouths a toad gets an immediate lesson in bad taste: the secretions are intensely bitter and cause nausea. At the severe end, the cardiac glycosides in toad venom can interfere with heart function and, in small animals, cause cardiac arrest.3Oxford Academic. Transcriptomic Analysis Reveals Potential Candidate Pathways and Genes Involved in Toxin Biosynthesis in True Toads For a human, squeezing an American toad and getting secretions on your skin is not dangerous, but getting it in your eyes or mucous membranes will hurt. The old myth that touching a toad gives you warts is baseless. The old observation that toads are foul-tasting to predators is entirely accurate.
Poison, Venom, and Why the Language Matters
People often use “poisonous” and “venomous” interchangeably, but the distinction is straightforward and helps clarify the actual risk from Maryland’s amphibians. A poison is a toxic substance that causes harm when ingested, inhaled, or absorbed through the skin. A venom is a toxic substance delivered through a wound, like a snakebite or a bee sting. Researchers have formalized this by categorizing biological toxins into three groups: poisons that lack a delivery mechanism and must be eaten or absorbed, venoms that are injected through a wound, and a third category called “toxungens” that are delivered to the body surface without a wound.4PubMed. Poisons, toxungens, and venoms: redefining and classifying toxic biological secretions and the organisms that employ them
By this framework, Maryland’s frogs and toads are genuinely poisonous, not venomous. They have no fangs, stingers, or spines. Their toxins sit passively on the skin and do their work only when a predator bites or mouths them, or when the secretions contact mucous membranes. A toad secretion that lands on a dog’s tongue and gets absorbed through the gums is acting as a poison. This is why calling these animals “poisonous” is correct even though casual conversation tends to reserve that word for things you eat. The frog or toad is a passive carrier; the predator does all the delivering.
The Danger to Dogs and Cats
The most practical concern about toxic amphibians in Maryland has four legs. Dogs, especially young and curious ones, frequently grab toads in their mouths, and the results can be alarming. Because toad toxins are rapidly absorbed through the mucous membranes of the mouth and digestive tract, symptoms appear quickly after contact.5Journal of Venomous Animals and Toxins including Tropical Diseases. Toad poisoning in three dogs: case reports
The clinical picture depends on how much toxin the dog was exposed to and which species of toad was involved. In mild to moderate cases, you will see heavy drooling, pawing at the mouth, vomiting, and sometimes diarrhea. More concerning signs include an abnormal heart rhythm, uncoordinated walking, depression, and neurological disturbances like circling. In severe cases, seizures, pulmonary edema, and even death can follow.6Journal of Venomous Animals and Toxins including Tropical Diseases. Toad poisoning in three dogs: case reports
Maryland’s American toads and Fowler’s toads are less dangerous than the much larger cane toads (Rhinella marina) found in the southern United States and tropics, which produce vastly more toxin due to their size. Still, a small dog mouthing an American toad can end up at the emergency vet. If you see your dog grab a toad, the standard first-aid advice is to rinse the dog’s mouth with water (pointing the head downward so the rinse water flows out rather than down the throat) and watch for any of the symptoms listed above. If you see heart irregularities, neurological signs, or seizures, that is a veterinary emergency.
Cats are generally less likely to mouth toads than dogs are, but they are not immune. A cat that bats at a toad and then licks its paw can get a dose of toxin. The same signs apply: drooling, vomiting, and in rare cases, cardiac or neurological effects.
Why You Will Never Find a Dart Frog in a Maryland Stream
When most people search for “poisonous frogs,” the mental image is a tiny, brilliantly colored frog from a nature documentary, the kind found in the rainforests of Central and South America. Those are poison dart frogs (family Dendrobatidae), and they are fundamentally different from Maryland’s toxic amphibians in several ways that go beyond geography.
Dart frogs get their toxins from their diet, primarily from ants, mites, and beetles that themselves produce alkaloid compounds. A dart frog raised in captivity on fruit flies loses its toxicity within a generation. Maryland’s toads, by contrast, manufacture their own toxins internally regardless of what they eat. This dietary dependence means dart frogs are locked into tropical ecosystems with the specific arthropod prey that supplies their chemical defenses. Maryland’s climate, insect fauna, and habitat simply cannot support them.
The vivid coloration of dart frogs serves as a warning signal to predators, a strategy called aposematism. Research on strawberry poison frogs has shown that the brightness and conspicuousness of a frog’s coloration correlates with how frequently birds attack frog-shaped models across different populations, suggesting that conspicuousness honestly signals toxicity to avian predators.7PLOS ONE. An Analysis of Predator Selection to Affect Aposematic Coloration in a Poison Frog Species Maryland’s pickerel frog takes a much subtler approach: its drab brown patterning provides camouflage rather than a warning, and its yellow-orange leg coloring is only visible when the frog jumps. American toads are similarly camouflaged, relying on their foul secretions as a backup plan rather than broadcasting their toxicity to every passing hawk.
Occasionally, someone in Maryland keeps exotic dart frogs as pets, which is legal with appropriate permits depending on the species. These captive-bred frogs are almost universally non-toxic because they are raised on diets that do not include the alkaloid-producing invertebrates of their native habitat. A captive blue poison dart frog in a terrarium in Baltimore is essentially a harmless, very pretty animal.
How Pollution Weakens Frog Chemical Defenses
An angle that rarely comes up in conversations about toxic frogs is that the chemical defenses of amphibians are themselves vulnerable to environmental contamination. The antimicrobial peptides that protect frogs from skin infections and help deter predators can be disrupted by agricultural runoff and wastewater.
Research on amphibians exposed to agricultural runoff and treated wastewater effluent found that these exposures altered both the amount and the effectiveness of protective skin peptides. Even when exposure increased the total protein content of skin secretions, the biological activity of those secretions against pathogens decreased.8PubMed. Effects of atrazine, agricultural runoff, and selected effluents on antimicrobial activity of skin peptides in Xenopus laevis In other words, a frog living downstream of farmland or a sewage treatment plant may produce skin secretions that look normal in quantity but are functionally impaired, leaving the animal more vulnerable to the chytrid fungus and other skin pathogens that are devastating amphibian populations worldwide.
Maryland is a state with significant agriculture, particularly on the Eastern Shore and in the Piedmont, and its waterways receive substantial agricultural and municipal runoff. For species like the pickerel frog, whose skin chemistry doubles as both a microbial defense and a predator deterrent, this kind of environmental degradation could erode both functions simultaneously. The frog’s chemical shield gets weaker at the same time that environmental stressors are increasing.
Biomedical Interest in Frog Skin Chemistry
The same skin secretions that make Maryland’s pickerel frog unpleasant to handle have drawn the attention of biomedical researchers looking for new antimicrobial compounds. With antibiotic-resistant bacteria becoming a growing clinical problem, natural peptides that kill bacteria through different mechanisms than conventional antibiotics are valuable leads for drug development.
The pickerel frog’s secretions are a particularly rich source. The 22 antimicrobial peptides isolated from its skin span multiple structural families, and some show both high potency and a broad spectrum of activity against different types of bacteria and yeast.9PubMed. Multiple antimicrobial peptides and peptides related to bradykinin and neuromedin N isolated from skin secretions of the pickerel frog, Rana palustris Beyond the antimicrobials, researchers also found peptides structurally related to bradykinin, a molecule involved in blood pressure regulation and inflammation in humans. The presence of a bradykinin molecule identical to the human version in a frog’s skin is a striking example of how conserved some of these chemical pathways are across vertebrates.
None of this has yet produced a drug you can buy at a pharmacy, and the gap between “interesting peptide isolated from frog skin” and “approved therapeutic” is enormous. But it does mean that the unassuming brown frog sitting on a rock in a Maryland creek is carrying a small pharmacy of bioactive molecules on its back, molecules that researchers are actively studying for potential applications against drug-resistant infections.
Identifying Maryland’s Toxic Amphibians in the Field
If you spend time outdoors in Maryland and want to know which amphibians to handle carefully, here is what to look for:
- Pickerel frog: Tan or light brown with two parallel rows of roughly rectangular dark spots down the back. The inner thighs and groin area show a distinctive yellow or orange color. Found near cool, clear streams, springs, and shaded ponds. Often confused with the similar-looking leopard frog, which has rounder spots and lacks the yellow-orange on the legs.
- American toad: Warty brown or reddish-brown skin with one or two large warts per dark spot on the back. Large parotoid glands behind the eyes that do not touch the cranial ridges. Found almost everywhere, from forests to suburban gardens. The most common toad across most of Maryland.
- Fowler’s toad: Similar to the American toad but with three or more small warts per dark spot, and parotoid glands that touch the cranial ridges. More common in sandy, open habitats and the coastal plain. Often found near river floodplains and beaches.
Every other frog species in Maryland, including green frogs, bullfrogs, wood frogs, spring peepers, gray tree frogs, and the various chorus frogs, produces skin secretions that may taste bad to a predator but are not meaningfully toxic to humans or pets. You do not need to worry about handling them beyond the general advice to wash your hands afterward, which protects the frog from chemicals on your skin as much as it protects you from anything on theirs.
One common point of confusion involves the Eastern spadefoot, sometimes found in sandy soils of Maryland’s coastal plain. Spadefoots are sometimes reported to cause skin irritation when handled, and their skin secretions can indeed cause a mild allergic-type reaction in some people, including sneezing and watery eyes. They are not in the same league as pickerel frogs or toads in terms of toxicity, but they are worth mentioning because the reaction can be surprising if you are not expecting it.
Handling Amphibians Safely
Whether you are a hiker, a gardener who finds toads under flowerpots, or a parent whose child just caught something at the creek, a few habits go a long way. Do not rub your eyes or touch your face after handling any frog or toad. If you handle a pickerel frog or a toad, wash your hands with soap and water. If your dog grabs a toad and starts drooling heavily, rinse its mouth and call your vet.
For the amphibians themselves, the bigger risk in most encounters is going the other direction: human skin oils, sunscreen, and insect repellent are harmful to frogs and toads, whose permeable skin absorbs chemicals readily. If you want to pick up a frog for a closer look, wetting your hands first helps. Keeping the interaction brief and putting the animal back where you found it is the kindest approach for both parties. The frog would rather you did not pick it up at all, and its skin chemistry is its way of saying so.