UPSC Prelims 2024 Q29: Poisonous Butterflies, Fish and Frogs Explained
Consider the following:
1. Butterflies
2. Fish
3. Frogs
How many of the above have poisonous species among them?
- Only one
- Only two
- All three
- None
Answer: (c) All three
Statement-wise explanation
- 1: correct — Several butterflies are poisonous to eat. Monarch caterpillars feed on milkweed and store its cardenolides (cardiac glycosides) in their bodies, and the adults keep these toxins. In feeding experiments, birds that ate monarchs vomited. Indian milkweed butterflies such as the Plain Tiger and the Common Crow also store plant toxins, and their bright colours warn predators.
- 2: correct — Pufferfish carry tetrodotoxin, a nerve poison found mostly in the liver and ovaries. It blocks sodium channels in nerves and muscles and can cause paralysis. Cooking does not destroy it. In Japan, where puffer (fugu) is eaten, only licensed chefs may prepare it, and pufferfish poisoning still kills a few people each year.
- 3: correct — Poison frogs (family Dendrobatidae) of Central and South America secrete toxins through their skin. The golden poison frog (Phyllobates terribilis) of Colombia's Pacific coast carries batrachotoxin, one of the strongest nerve poisons known. Indigenous hunters rubbed dart tips on these frogs, which gave them the name poison-dart frogs.
How to eliminate
There is no reliable shortcut here. You either know that each group has toxic members or you don't. Two of the groups are well known: pufferfish (tetrodotoxin) and poison-dart frogs (batrachotoxin) are textbook examples. That rules out 'None' and 'Only one' and leaves 'Only two' or 'All three'. Butterflies decide it. Remember the monarch: it stores milkweed toxins and warns birds with its bright orange colour. Another clue: the question asks whether the groups have poisonous species 'among them', not whether every member is poisonous. Large groups like fish, frogs and butterflies, with thousands of species, almost always include at least one toxic species.
Know more
Poisonous vs venomous
A poisonous animal harms you when you eat or touch it. The toxin is passive and sits in its skin or tissues. A venomous animal injects toxin through fangs, stings or spines. Pufferfish are poisonous. Stonefish and cobras are venomous.
Where the toxin comes from
Many poisonous animals do not make their own toxin. They take it from their food, which is called sequestration:
| Group | Example | Toxin | Source |
|---|---|---|---|
| Butterflies | Monarch, Plain Tiger, Common Crow | Cardenolides (cardiac glycosides) | Milkweed and related plants eaten by the caterpillar |
| Fish | Pufferfish (fugu) | Tetrodotoxin | Marine bacteria, built up through the food chain |
| Frogs | Golden poison frog | Batrachotoxin | Diet of small arthropods. Captive-bred frogs lose their toxicity |
Warning colours (aposematism)
Toxic species often have bright colours, such as orange monarchs and yellow or blue poison frogs. Predators learn to avoid them.
Mimicry
- Batesian: a harmless species copies a toxic one. Some female Danaid Eggfly butterflies look like the Plain Tiger.
- Müllerian: two toxic species look alike and share the protection.
How toxins work
Tetrodotoxin and batrachotoxin both act on sodium channels in nerves. Tetrodotoxin blocks them and batrachotoxin forces them to stay open. Either way, the result is numbness, paralysis and, in severe cases, death. Cardenolides block the Na⁺/K⁺-ATPase pump. Monarchs have evolved changes in this pump that make them resistant to the toxin.
Exam angle: UPSC likes questions of the form 'how many of these have X'. Check each group on its own and remember that a single species is enough to make the statement true.