pesticide used against insects
An insecticide is a poison made to kill insects and spiders.
Insects are very tough animals that have adapted to a great variety of settings. Therefore, the poison used to kill them is also deadly to humans. There can be great danger of eating pesticide when you have vegetables. This is why often people will rub an apple on their jumper before eating it. This adds a nice shine to the apple and rubs away some of the pesticides. If you do not clean the jumper there is a risk pesticide might build up.