parasite
https://gyazo.com/c850804095b3933f2fc8bf2c67ad887d
noun
1. an organism that lives in or on an organism of another species (its host) and benefits by deriving nutrients at the other's expense:
«…への» 寄生動物, 寄生虫; 寄生植物 «on, of» .
e.g. the parasite attaches itself to the mouths of fishes
e.g. an intestinal parasite of cattle.
Parasites exist in huge variety, including animals, plants, and microorganisms. They may live as ectoparasites on the surface of the host (e.g., arthropods such as ticks, mites, lice, fleas, and many insects infesting plants) or as endoparasites in the gut or tissues (e.g., many kinds of worm), and cause varying degrees of damage or disease to the host.
2. derogatory a person who habitually relies on or exploits others and gives nothing in return:
«…の» 居候（いそうろう）, 寄食者, 食客; 【人に】たかる人(sponger) «on»
e.g. the capitalist is really a parasite on the workers.
ORIGIN
mid 16th century: via Latin from Greek parasitos ‘(person) eating at another's table’, from para- ‘alongside’ + sitos ‘food’.