1. Toads Suddenly Appear Near a School in Tokyo's Chuo Ward
In Chuo Ward, Tokyo, the surroundings are mostly buildings and apartments. There are no fields, riverbeds, or forests. In front of a school in this urban area sits a pond the size of a bathtub. It is a simple puddle with water plants and goldfish, cared for by someone. Usually, it is a quiet pool of water. However, from late February to early March, a change occurs. Japanese common toads gather, croaking with low voices in the water and laying long, string-like eggs.
After a while, the adult toads disappear. Only the eggs remain, which eventually become tadpoles. Two mysteries arise here. First, where did they come from when there are no natural water bodies nearby? Second, if they are not in the pond most of the time, where do they spend the rest of the year? We tend to think of frogs as creatures of the water, but the answers to these questions lie in a place very different from that image.
2. What Is the Japanese Common Toad?
First, let us know our subject. The Japanese common toad is widely distributed in eastern Japan. Large individuals can reach about 15 cm (6 inches) in length. They have a stout body, warty skin, and are brown or gray. They are what people often call "gama-gaeru" (toad). Unlike tree frogs, they do not jump; they walk heavily and slowly. This makes them easy to catch, yet they have survived for a reason.
Instead of running away, they have poison. Behind their eyes are swollen areas called parotoid glands. When attacked, they secrete a white fluid, which is toxic. It is common to hear stories of dogs foaming at the mouth after biting them. While slight contact by humans is rarely a major issue, follow these rules: do not rub your eyes or mouth after touching them, always wash your hands, and keep pets away. If a dog or cat bites or licks them, wash their mouth with water and see a vet if they act strangely. The old "toad oil" sold in Japan has a name related to the secretions of this toad family, showing how this poison has appeared in Japanese culture.
They are nocturnal. Toads are active at night and hide under stones, fallen leaves, or in soil depressions during the day. That is why you rarely see them in parks during the day. They are not absent; they are hiding.
3. Where Toads Spend Most of the Year: On and in the Soil
Answering the first question: where are they usually? The conclusion is surprising. They are not in the water, but on or in the soil. Toads are relatively resistant to drying out among frog species. Therefore, outside of the breeding season, they rarely approach water bodies and can live in small green spaces in urban homes or temple grounds [2]. In the city, this means under trees at temples or shrines where leaves pile up, in school or apartment plantings, in home gardens, or in park thickets. They eat earthworms and insects there, staying still under soil or leaves during the day. By late autumn, they burrow into the soil to hibernate.
This is why they seem to "disappear" from the city. It is because they live in a way that is hard to see. They are active at night, hide in the soil during the day, and only visit water bodies for a few days to weeks each year. The few days they gather at the pond are the most visible time of the year. The rest of the time, they may be sitting quietly in the soil of a planting bed right next to the path you walk on.
4. Why Toads Walk to Ponds All at Once in February
In late winter, when cold days continue, this happens on nights with warm rain. Toads hibernating in the soil wake up and start walking toward ponds all at once. In Tokyo’s flatlands, this period is from mid-February to early March [1]. In mountainous parts of the same prefecture, it happens slightly later.
According to the story, males arrive at the pond first and wait. When females arrive, males swarm them, sometimes forming a ball around one female. People in the past called this scene "frog battle" [3]. For a few days, the pond is busy. Males croak with a low "kukukuku" sound. Unlike the loud image of frog calls, toad calls are surprisingly quiet and easy to miss.
The eggs laid by females are not round clumps but long, thin strings. Black dots line up inside transparent strings, and they lay thousands at once [4]. Large females can lay over 10,000. They attach these strings to water plants or branches. After laying eggs, adult toads leave the pond and return to land life. Only the eggs remain. Tadpoles hatch and become small toads in early summer, moving to land en masse.
Why do eggs survive in a pond with goldfish? Usually, fish eat eggs and tadpoles. However, toad eggs and tadpoles are thought to have poison, similar to the adult’s secretion. Because of this, many fish spit them out if they try to eat them. The survival of eggs in goldfish ponds may be due to this property. Water plants also help, as toads need something to attach their strings to. Why lay thousands? Because most do not become adults. Eggs and tadpoles are eaten by fish, insects, and birds. Only a very small number grow up enough to lay eggs. Winning by numbers is their survival strategy.
6. Why Urban Japanese Common Toads Are Decreasing
Unfortunately, urban Japanese common toads are decreasing. They are listed in the Tokyo Red Data Book [2]. Reasons include suburban housing development, green space reduction in central wards, traffic accidents during migration, and the loss of water bodies.
There is another hidden problem. In wards and other areas, toads brought by humans from other regions (Japanese toads) are mixing with the local population, causing concern about genetic disruption [2]. Even if they look similar, local populations have developed unique traits over long periods. Releasing individuals from elsewhere erases this history. "Letting them go because they look cute" can actually create problems.
Because toads return to the same pond every year, the small school pond is significant. It is one of the few places left in the concrete city where eggs can be laid. Even if small, if there is water, soil, and leaves, creatures can live there.
7. What to Do and Not Do When You Find Toads or Eggs
If you find toads or eggs at a pond, here is what to do. It is good to observe quietly, take photos or sketches, and record the date, location, and number. If you touch them, wash your hands. If you find a toad crossing a road, and you can do so safely, move it to the side it was heading toward. Do not take them home, release them in a different pond or river, pull or move the egg strings, or rub your eyes or mouth after touching them.
8. How to Investigate Your Nearby Pond Yourself
The next time it rains, looking at a pond might make you see it as a passage left in the city. Try checking a nearby pond the day after a warm rain in late February. If you find string-like eggs, that pond may be a breeding ground. Record the date, weather, and number of egg masses. If you record this every year, you can compare changes in the number of egg masses.
On a map of your neighborhood, mark places with soil and trees, such as parks, temples, schools, and large plantings. This becomes a map of creature habitats. Check if large roads lie between these marked places. Those roads are the "uncrossable rivers" for creatures. Toads are active at night. If you go outside at night to look, always go with an adult.