Words often get used in casual ways in everyday conversation. However, many words that we use interchangeably in casual speaking often have very different meanings. A good example of this is the words poisonous and venomous. Frequently, you hear people talk about “poisonous” snakes or spiders, but this is really not correct—snakes and spiders are not poisonous.
“Wait,” I hear you say, “I know that snake bites can be dangerous!”
Yes, that is true, but it is because some snakes are venomous. Venom is a toxin that is injected, often through biting or stinging. A poison is something that is ingested through eating or inhaling. So the bite of a dangerous snake can inject venom into your tissues, but if you eat that same snake it will not hurt you. On the other hand, mushrooms are not venomous—they do not bite or sting and inject venom, but they can be deadly poisonous if you eat them.
Many interesting and dangerous animals are venomous. Venom is used throughout the animal kingdom in diverse ways. For example, it can be used to secure food, as in spiders and snakes, and certain wasps that inject venom into their prey to lay eggs upon for their larva to eat (this is like in the movie Aliens where humans were food for juvenile creatures from outer space—nature did it first before Hollywood. Check this out for more interesting science facts).
Venom is also used for defense. Honey bees do not need venom to secure their food, but rather will defend their food and colony through stinging. And vemon can be used to fight with individuals of the same species. Male duckbilled platypuses have spines on their back legs that they use to inject venom into would-be rivals for female attention.
So, now you know the difference, and when someone at a yard party hollers out “Don’t sit there! There’s a poisonous black widow right there,” You can give a knowing smile as you sit and say “Actually, the spider is venomous. Let me tell you all about it.”