Armillaria mellea in the context of "Parasitic"

Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson characterised parasites' way of feeding as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes.

There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration, directly transmitted parasitism (by contact), trophically-transmitted parasitism (by being eaten), vector-transmitted parasitism, parasitoidism, and micropredation. One major axis of classification concerns invasiveness: an endoparasite lives inside the host's body; an ectoparasite lives outside, on the host's surface.

Armillaria is a genus of fungi that includes the A. mellea species ('honey fungus') that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as A. mellea. Armillaria sp. are long-lived and form the largest living fungi in the world. The largest known specimen (an A. ostoyae) covers more than 3.4 square miles (8.8 km) in Oregon and is estimated to be 2,500 years old. Some species of Armillaria display bioluminescence.

Armillaria can be a destructive forest pathogen. It causes "white rot" root disease. As it feeds on dead plant material, it can kill its host with little negative effect to itself.