A
parasite is an
organism that lives in or on the living tissue of a
host organism at the expense of that host. The
biological interaction between the host and the parasite is called
parasitism. Parasitism is a type of
symbiosis, by one definition, although another definition of symbiosis excludes parasitism, since it requires that the host benefit from the interaction as well as the parasite.
Parasites are generally smaller than their hosts, absorbing nutrients from the host's body fluids, but this is far from a universal strategy.
Organisms whose life cycle guarantees the death of the host are not called parasites, but are
parasitoids.
A few parasites have hosts which are themselves parasites. These are called
hyperparasites.
Examples
- Ectoparasites (''ecto'' = outside; parasites that live on but not within their hosts, for example, attached to their skin)
- * Plants
- ** Cuscuta
- ** Mistletoe
- ** Toothwort
- ** The woodrose, Dactylanthus taylorii
- * Animals
- ** Hirudinea (some leeches)
- ** Phthiraptera (Lice)
- ** Siphonaptera (Fleas)
- ** Acarina (Ticks)
- ** Tantulocarida
Many lifeforms are parasitic only during a part of their lifecycle. Many
cuckoos, for example, are
brood parasites: their young are parasitic on the host species, but adult cuckoos fend for themselves. In some cases, it may even be useful to view an embryo as a parasite of its mother (see
parent-offspring conflict). This usage is controversial when applied to humans because it affects the perceived morality of
abortion.
http://www.l4l.org/library/notparas.html
The term parasite is also used for people who benefit from a relationship, society or system without contributing significantly to it, although they could; however this usage of the term is highly controversial because of its association with
Nazism and its various extermination programs.
See also
References
Category:Parasitology
Category:Ecology
da:Snylter
es:Parásito
eo:Parazito
fr:Parasite
he:טפיל
nl:Parasiet
ja:寄生虫
pl:Pasożyt
pt:Parasita