Venenoso vs. ponzoñoso
Both venenoso and ponzoñoso translate to poisonous or venomous in English, but they have subtle biological and usage differences in Spanish. While venenoso is a broad, everyday term for anything containing toxins, ponzoñoso specifically refers to organisms that actively inject venom, or is used to describe deeply malicious figurative situations.
Venenoso
B1The word venenoso is a general term used to describe plants, animals, or substances that contain poison and are harmful if ingested, inhaled, or touched. In everyday conversation, it is the most common word used to describe any toxic creature, whether it bites or is eaten, as well as figurative toxic behaviors.
No debes comer esa seta porque es muy venenosa.
(You should not eat that mushroom because it is very poisonous.)
El gas emitido por la fábrica abandonada es altamente venenoso.
(The gas emitted by the abandoned factory is highly poisonous.)
Me alejé lentamente de la rana venenosa en la selva.
(I slowly walked away from the poisonous frog in the jungle.)
El zoológico tiene un terrario especial para la serpiente venenosa.
(The zoo has a special terrarium for the venomous snake.)
Su actitud venenosa destruyó nuestro grupo de amigos.
(Her poisonous attitude destroyed our group of friends.)
Ponzoñoso
C1The word ponzoñoso specifically refers to animals that have a specialized apparatus, like a stinger or fangs, to actively inject venom into their prey or attackers. It is frequently used in medical and biological contexts to describe venomous bites or stings, and figuratively to describe extremely malicious, destructive, or spiteful intentions.
Tuvimos mucho cuidado con los escorpiones ponzoñosos en el desierto.
(We were very careful with the venomous scorpions in the desert.)
El hospital municipal cuenta con suero para la picadura de animales ponzoñosos.
(The municipal hospital has antivenom for the sting of venomous animals.)
La mantarraya usa su cola ponzoñosa para defenderse de los depredadores.
(The stingray uses its venomous tail to defend itself against predators.)
Se difundió un chisme ponzoñoso por toda la oficina esta mañana.
(A malicious gossip spread throughout the office this morning.)
Lanzó una mirada ponzoñosa antes de salir dando un portazo.
(He shot a venomous glare before storming out and slamming the door.)
Summary
In short, use venenoso as the general everyday term for anything that contains poison, whether inhaled, consumed, or touched. Use ponzoñoso when you want to be biologically precise about animals that actively inject venom through a bite or sting, or when describing exceptionally malicious words and actions.