On your head be it



Robert Adlard at the Queensland Museum in Brisbane, Australia, calls parasites "intimate aliens". "They are horrific when you find out what they do, but they have a bizarre and miniature beauty that is stunning," he says. According to Adlard, 30 to 50 per cent of life on Earth is parasitic.



Pediculus capitis (left) is a parasitic louse found only on humans. The heat from our scalp allows its eggs to hatch in about a week, and the lice then live for just over a month.



Infestation from P. capitis is the most prevalent external parasitic infestation in humans worldwide. Unlike body lice, head lice do not transmit diseases, and their infestation symptoms are relatively mild.



Journal reference: Pesticide Biochemistry and Physiology, DOI: 10.1016/j.pestbp.2009.04.017).



(Image: Cath Covacin/Stephen Barker/Rick Webb/The University of Queensland, Australia)

Lousy feather



This small pigeon louse, Campanulotes bidentatus, was spotted on the feather of a pigeon. There are over 5000 louse species, at least five of which live on pigeons.



Feather lice have claws that enable them to grasp onto feathers. They live their entire life on a bird's body. Unlike other parasites – such as malaria, which uses mosquitoes to get into humans – the pigeon louse relies on direct contact between birds to spread to new hosts.



Campanulotes bidentatus is part of the order Phthiraptera, and has a flattened body and three pairs of legs. The body length of adults ranges from 0.3 to 12 millimetres, and their antennae are short, with four segments.



(Image: Cath Covacin/Stephen Barker/Rick Webb/The University of Queensland)

Gutting work



Tapeworms are an ancient group of intestinal parasites that live in the guts of a wide range of animals including mammals, birds and reptiles. Living in the intestine means they must battle with constant muscular contractions. To allow for this, they have adapted suckers and hooks on their heads, shown in extreme close-up here.



"Many parasites have lost the ability live independently of their host," says Malcolm Jones at the University of Queensland. The tapeworm, for example, does not have an intestinal canal and relies on its host to break down and digest food. "They then feed through their skin," says Jones.



(Image: Mal Jones/Queensland Institute of Medical Research/The University of Queensland, Australia) Advertisement

Swimming squirmer



Amidst the beauty of the Great Barrier Reef off the coast of Queensland, Australia, are serranid fish, and deep inside them squirms this Trypanorhynch tapeworm. This image shows part of the tapeworm's head with four tentacles poking out.



This parasite patiently waits for its host to be eaten by a shark. And once inside the shark, it will use the hooks from its tentacles to grab the shark's stomach lining. There, it will settle in and lay its eggs.



Adlard says the parasite is unlikely to harm the fish or shark, as it doesn't reproduce in high enough numbers.



(Image: Rob Adlard, Queensland Museum, Australia)