Pesticide is a chemical or biological compound or agent (such as a virus, bacterium, or fungus) that deters, incapacitates, kills, or otherwise discourages pests. Target pests includes insects, plant pathogens, weeds, molluscs, mammals, fish, nematodes (roundworms) and microbes that destroy property, cause nuisance, or spread disease, or are disease vectors. Apart from that some pesticides have benefits; some also have drawbacks, such as potential toxicity to humans and other species and living things.