Venoms, poisons and chemical weapons: the invisible battle

How marine animals defend themselves and capture prey

A scorpionfish stays hidden until prey comes within reach. A brightly coloured nudibranch may be conspicuous enough to warn a predator away. An anemone can catch food without leaving its patch of seabed. To understand the role of chemistry in each encounter, start with how the substance reaches the other animal.

By DIVE.EXPLO360.FR · 11/11/2026

The scorpionfish in ambush

Camouflage lets a scorpionfish wait for prey without being seen. The spines associated with venom glands mainly serve in defence. If an attacker is pricked, venom can enter through the puncture.

A scorpionfish lying in wait beneath small silver fish. — A motionless scorpionfish can ambush prey once it comes within reach. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

A silvery pufferfish above sand. — Some puffers contain poisonous substances that can reach a predator when swallowed. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

Stinging or being swallowed

A scorpionfish spine delivers venom through a wound. In some pufferfish, tetrodotoxin can act after ingestion. It blocks certain sodium channels and disrupts signalling in nerves and muscles. Toxicity varies among species and among individuals.

Three ways an encounter can end

Defend

A scorpionfish spine can interrupt an attack.

Catch

An anemone brings prey towards its mouth.

Deter

Unpleasant prey may be spat out.

How nudibranchs defend themselves

Nudibranchs may obtain defensive molecules through food or make them themselves. Research on Dendrodoris limbata showed that this sea slug could produce a defensive compound itself. Contrasting colours sometimes act as warnings, depending on what the predator can perceive.