Interspecific Relationships - Negative Interactions > Parasitism

Parasitism is an interaction between two species in which one (known as parasite) obtains its food in ready‑made form from the other living organism (said to be host).

1. Ectoparasites vs. Endoparasites

2. Brood Parasitism

• Parasite lays eggs in the host's nest → host raises parasite's young
• Example: Koel (Eudynamys scolopaceus) lays eggs in a crow's nest
• Koel eggs show egg mimicry (match crow eggs in colour & pattern)
• Koel hatches earlier (~12–13 days) than the crow (~16–17 days)

3. Plant Parasitism

• Cuscuta (dodder): Rootless, leafless stem parasite; attaches via haustoria
• Mistletoe: Hemi-parasite; can photosynthesise but takes water from host
• Orobanche: Holoparasite of legumes; no chlorophyll

A-C. Animal ectoparasites: A. mite (ventral view); B. tick (dorsal view); C. bedbug (dorsal view)

A-G. Animal endoparasites: A. Taenia (tapeworm); B. Ascaris (round worm); C. Entamoeba; D. Plasmodium (malarial parasite); E. Schistosoma (blood fluke); F. Wuchereria (filarial worm); G. Trypanosoma

A-E. Parasitic plants: A. Cuscuta; B. Orobanche; C. Balanophora; D. Rafflesia; E. Viscum

• Parasitism is an interaction where one organism (the parasite) derives ready-made nourishment directly from another living organism (the host).
• Ectoparasites (like ticks and lice) live on the host's outer surface and retain functional organs, whereas endoparasites (like tapeworms and Plasmodium) live inside the host with reduced sensory and digestive systems.
• In brood parasitism, a bird lays its eggs in the nest of a host species, often using egg mimicry and earlier hatching times to ensure the host raises its young (e.g., the Koel bird and the crow).
• Plant parasites use specialised structures to extract nutrients; they can be total parasites lacking chlorophyll entirely (like the leafless Cuscuta) or partial parasites that still photosynthesise (like Mistletoe).
• Parasites possess unique survival adaptations, including specialised attachment organs (hooks and suckers), the ability to absorb food directly through their skin, anaerobic respiration, and massive reproductive capacities involving intermediate hosts.