noun
parasite; parasitic organism
Technical biological term for an organism that lives on or in another organism and benefits at the host's expense.
活物寄生は宿主なしでは生きられない。
A parasite cannot live without a host.
寄生虫 is the common everyday word for 'parasite', while 活物寄生 is a more formal, technical term used mainly in biology.
Compound of 活物 (living thing) and 寄生 (parasitism). The exact historical derivation is uncertain; the term is used in modern biological contexts.