1. How a Skunk Makes and Sprays Its Smelly Chemicals
The smell of the striped skunk comes from two glands located on either side of the anus. The main ingredients are chemicals called thiols, which contain sulfur and hydrogen. Specific compounds include (E)-2-buten-1-thiol and 3-methyl-1-butanethiol [3].
Skunks do not attack without warning. Before spraying, a striped skunk raises its tail, stamps its feet, and hisses to warn the threat [4]. If the threat continues, the skunk sprays. The distance varies by source, but it is often cited as about 3 m (about 10 feet), and the aim is precise [4].
Why does the smell return after washing? According to the University of Bristol, the spray contains thiols and thioacetates. Thioacetates smell less strongly than thiols. However, when water slowly breaks down thioacetates, it releases the strong-smelling thiols again. This is why the smell can return days later when the animal or object gets wet [3].
2. Sorting Toxic Animals by How They Deliver Their Toxin
In 2014, Nelsen and colleagues proposed classifying toxic creatures by "how they deliver" the toxin, rather than "how they make" it. They defined three types. Venom is delivered by creating a wound and entering the body. Toxungen is delivered to the body surface without creating a wound. Poison has no delivery mechanism; it works when eaten or absorbed through the skin [1].
In Japanese, it is easier to distinguish them by action: "biting" is venom, "spraying" is toxungen, and "eating" is poison. Note that toxungen is an academic proposal and is not yet widely used in general language.
Where does the skunk fit? The definition of toxungen includes secretions that reach the body surface without biting or stinging, such as sprays or spitting [2]. Since skunk spray reaches the surface without a bite or sting, it is closer to toxungen than venom. Importantly, this classification describes "how it gets there," not "how dangerous it is." The harmfulness of skunk spray itself is not judged by this method [1].
3. How Bombardier Beetles Mix Chemicals to Spray 100°C Liquid
The glands in the abdomen of bombardier beetles are divided into a large storage chamber and a small reaction chamber. The storage chamber holds hydroquinone and hydrogen peroxide. The reaction chamber holds enzymes called catalase and peroxidase [5].
When the beetle feels danger, it mixes the two substances. This produces oxygen and oxidizes the hydroquinone. The oxygen produced also helps push the liquid out. The beetle stores the materials separately and mixes them only when needed [5].
Research reports that the spray from some bombardier beetles reaches 100°C (212°F). The liquid contains p-benzoquinone, a known irritant. One beetle can spray more than 20 times before its glands are empty [5]. Japanese ground beetles, such as the *Miyadera* beetle (also called "farting beetle"), have similar weapons. However, the specific numbers cited here come from studies on bombardier beetles, not measurements of the Japanese species themselves [5].
Because the spray goes to the body surface without causing a wound, it fits the "spraying" type, similar to the skunk [5].
When threatened, the stored chemicals mix. Mixing them produces oxygen, and the enzymes help oxidize hydroquinone [5].
4. Why Poison Dart Frogs Get Their Poison From the Food They Eat
The poison of poison dart frogs is made of alkaloids. They do not create these alkaloids themselves. Instead, they acquire them from eating arthropods like ants and mites [6]. In captivity, groups fed only fruit flies lost their poison. However, this report is a preprint (not yet peer-reviewed), so it should be read alongside other sources [6].
A 2007 study by Saporito and others found more than 80 types of alkaloids in wild mites. Of these, 41 types were also found in the skin glands of strawberry poison dart frogs. About half of the mite alkaloids were also found in the frog [7]. This suggests that mites are a main source of the frog's poison.
There is no mechanism to deliver the poison. It does not bite or spray. It works only when an enemy eats it or touches the skin. This fits the definition of poison in the three-part classification [1]. Making poison and delivering poison are separate issues.
5. How the Keelback Snake Borrows Frog Poison for Its Neck Gland
The keelback snake has an organ called the "neck gland" under the skin on the back of its neck. It uses this to protect itself from predators. The main component of the poison is bufadienolide, a cardiac steroid. A study by Kyoto University shows this poison comes from the toads the snake eats [8].
When the diet changes, the source of the poison changes. The *Itsuuroko* keelback snake in southwestern China eats earthworms. Even though it does not eat toads, its neck glands still contain bufadienolide. The material for this poison comes from fireflies. Research by Akira Mori, Naoki Mori, and colleagues at Kyoto University, published in PNAS on February 25, 2020, suggests that as the snake's diet shifted from frogs to earthworms, researchers suggest the source shifted from toads to fireflies [8].
The sources listed here do not explain how the poison in the neck gland is delivered to an enemy. Therefore, we cannot decide which of the three categories it fits into [8].
6. Try Sorting Animal Weapons by How They Are Delivered
In encyclopedias or at the zoo, choose an animal with a weapon. Ask: Is it delivered by making a wound (venom), spraying on the surface (toxungen), or being eaten (poison)? Write the reason in your notebook. Also, note separately whether the animal makes the poison itself or borrows it.
It is okay if you cannot decide. This classification was proposed in 2014, and there are many ambiguous cases [1].
If you want to read more, the story of keelback snakes and fireflies is in Kyoto University research news (March 3, 2020) in Japanese. The original text for the three-part classification is the 2014 review by Nelsen et al. A next question to explore is: How much do foods other than mites contribute to poison dart frog poison? Are there other animals that "borrow" poison?