Parasites exist at the expense of the host: by living on (ectoparasites) or in (endoparasites) the host and deriving nourishment from it. Examples of parasites include tapeworms, flukes, roundworms, pentastomes, fleas, lice and ticks.

Parasitic creatures fascinate people, especially parasites that live inside domestic animals and humans. There are also livestock parasites that impact on our food safety and security and wildlife parasites that affect our native animal populations.

Parasitic animals are broadly grouped into the single-celled (protists), the worms (helminths) and those with hard external skeletons (arthropods). Most people will have had a personal encounter with a parasite, although many people choose to have a selective memory about such events. These experiences may include:

• malaria or giardia infections (protists) — causing stomach upsets;

• pinworms (helminths) and head lice (arthropods) in children;

• impressively large intestinal worms (helminths) — from accidentally consuming parasite eggs or infected meat while travelling in tropical countries overseas.

If you have a dog or a cat, you may have encountered a parasitic menagerie at some time including:

• roundworms or tapeworms (helminths); or

• fleas or ticks (arthropods).

The Museum's Parasitology Collection is entirely worm- or helminth-based.

What makes parasites so interesting?

It is estimated that more than 50% of all animal species are parasitic at some stage in their life history. That makes parasitism one of the most dominant ecological interactions in biology. There are many parasitic relationships to study. For every parasite species we know something about, countless others remain unknown.

Some parasites have very complex lifecycles and must infect several different animal and/or plant species before the parasite can mature and reproduce. An example is a human tapeworm that could be acquired by eating infected meat such as pork or beef. Other parasites have direct lifecycles and infect only one animal species on which it matures and reproduces, like the head louse.

Parasites provide parasitologists with many exciting and interesting challenges, for example:

• what is their lifecycle?

• what impact does the parasite have on its host(s)?

• if harmful, what are the control options?

• how is an organism adapted for life as a parasite?

• how do parasites evolve?