Poison Ivy, the poison dart frog, and the substance that Joffrey from Game of Thrones ingested are all examples of things that are poisonous.
Venomous – refers to an organism that that can inject a toxin into another organism. You've probably heard someone say “poisonous snake” in reference to a rattlesnake. A rattlesnake is venomous, not poisonous. Eating it will not poison you.
Spiders, bees, snakes, and scorpions can all be venomous.