1. Why Was a Japanese Squirrel Seen Eating a Poisonous Amanita Mushroom?
In the forest, a Japanese squirrel was seen nibbling on a mushroom. This mushroom was a poisonous one from the Amanita family. Associate Professor Kenji Suejima from Kobe University and photographer Koichi Gomi observed this behavior in Nagano and reported it in an academic journal in December 2021 [1]. It did not seem to be a one-time accident, because the same squirrel returned to eat the Amanita mushroom several days later [1]. Mr. Gomi later confirmed that the squirrel also ate other poisonous types, such as the red fly agaric, the yellow fly agaric, and Russula emetica [2]. The research team concluded that it is highly likely this squirrel could eat these poisonous mushrooms safely [1]. However, the report does not explain the mechanism of why the squirrel is unaffected. This does not mean it is safe for humans to do the same thing, so people must not eat wild mushrooms.
The research team also offered a guess. If the spores of the poisonous mushroom survive digestion and are passed out with the squirrel’s droppings, the squirrel’s movement might benefit the mushroom [1]. But is the mushroom the squirrel’s usual main food? [1]
2. Are Mushrooms Just a Dessert for Japanese Squirrels, and What Is Their Main Food?
Mr. Gomi, who observed the mushrooms, stated that the Japanese squirrel’s main food is walnuts and chestnuts, and that they enjoy mushrooms like a dessert [2]. The phrase "like a dessert" reflects the observer’s impression and is not an academic conclusion. Looking at research reports, a similar picture emerges. The Japanese squirrel is one of the few diurnal animals in Japan, and it tends to rely heavily on a very small number of main foods, such as pine nuts and Japanese walnuts, depending on its habitat [3]. The Ministry of the Environment explains that they also eat acorns, mushrooms, and insects [4]. What they choose as main food seems to change based on what grows in the local forest. However, relying on few types of food means they face difficulties when those foods do not bear fruit.
3. How Do Japanese Squirrels Survive Seasons Without Walnuts and Pine Nuts?
Main foods like walnuts and pine nuts only bear fruit during limited times of the year. Therefore, reports state that Japanese squirrels use various foods, such as tree flowers, buds, grass, and mushrooms [3]. Another preparation is food storage. According to the Ministry of the Environment, Japanese squirrels do not hibernate [4]. They have a habit of burying food underground to prepare for winter [4]. Research reports also state that they cope with seasons when food is scarce through this food storage habit [3]. Since they do not hibernate, they need food even in winter. They use flowers, buds, and grass during periods when main foods are unavailable, and they rely on stored nuts to get through the cold months. Thinking about this, eating poisonous mushrooms appears to be one way the squirrel makes broad use of available food sources.
4. What Happens to Walnuts That Japanese Squirrels Bury and Never Retrieve?
Japanese squirrels store Japanese walnuts one by one in separate locations, a behavior called dispersed storage. Besides burying them in the ground, they sometimes wedge them into tree forks. In tracking studies, most were moved to nearby places within 15 m (about 50 feet), but some were carried as far as 168 m (about 550 feet), which is farther than the long side of a soccer field [5]. In one survey, 156 walnuts fitted with transmitters were tracked until spring [5]. 65 were eaten immediately, and the remaining 91 (44 in trees, 47 on the ground) were stored. Of those 91, 19 were eaten by red-backed voles, 61 were retrieved by the squirrel, and 11 remained unretrieved until spring [5]. Calculating these 11, they represent about 7% of the total 156, and about 12% of the 91 stored [5]. It is explained that these 11 had a chance to germinate [5]. This does not mean they all germinated, and since these are numbers from one survey, the results may not be the same in every forest. As another example, though not about squirrels alone, there is an explanation that acorns are hard to sprout if they just fall naturally, but those shallowly buried by birds or animals can sprout [6]. Still, the numbers suggest that squirrel leftovers can lead to new trees in the forest.
5. How Can You Check the Numbers and Find the Main Food in Your Area?
Try this: check the numbers in this article yourself. Add 65 and 91 to see if they equal 156. Add 19, 61, and 11 to see if they equal 91. You can use a calculator to divide 11 by the total to see if it matches the "about 7%" mentioned in the article. Another thing to try is to find out what the main food is for squirrels in the area where you live. Since main food changes by environment, local nature observation materials or museum explanations might list the main food for that specific land [3]. If you see a squirrel in a forest or park, please watch it quietly from a distance without approaching. Do not eat wild mushrooms.