Peculiar Parasites

Disclaimer: this is not a review of a recent Oscar-winning film.

The natural world is home to many amazing and often frankly bizarre organisms and I would like to take some time to highlight what I believe to be rather astonishing techniques used by parasites to aid their survival. A parasite is an organism which lives in or on another host organism in order to derive a benefit - e.g. nutrient resources to the detriment of the host organism.

(1/4) THE ZOMBIE DEATH GRIP - Ophiocordyceps unilateralis and the carpenter ant.

This parasite is a fungus which infects the carpenter ant. When the ants are exposed to the fungal spores they can penetrate the exoskeleton (outer layer) entering the body of the ant. From here, the fungus releases chemicals in order to hijack the brain and nervous system and control the muscles. This manipulation of the ant causes it to leave the comfort of its own nest and climb the forest vegetation to a height that is optimal for the spread of the fungus. From here the fungus takes control of the mandibular (bite) muscles of the ant, causing it to clamp onto the underside of the leaf. The ant hangs there with this ‘death grip’ as the fungus digests the ant from the inside. Upon completion the fruiting body (stalk structure) of the fungus sprouts out of the ant's head, ready to release new spores to infect more ants.

Image - Fruiting body forms out of the head of the ant to release spores into the air.

(2/4) DISCO EYES - Leucochloridium paradoxum and the land snail.

A parasitic worm which has two different hosts, a snail and a bird, Leucochloridium has evolved an extremely cunning way of ensuring it completes its life cycle. Upon parasitising the snail, the worm invades the eyestalks, where it pulsates, causing the eyestalks of the snails to look like caterpillars. Influencing the snail’s behaviour, the worm causes the snail to crawl out into the open, where those wriggling eyestalks appear too tempting for a passing bird. When the bird eats the snail, the worm enters the bird and produces eggs which are released in the bird's faeces ready to be eaten by another snail, completing the cycle.

Image - Parasite causes snail's eyestalks to look like wriggling caterpillars.

(3/4) INTERNAL WATERBOARDING - Spinochordodes tellini and the grasshopper.

Initially infecting and developing in a grasshopper or cricket as a host, this parasitic worm has the problem of needing to find water, as the adult stage of its life cycle is one of an aquatic existence. As a result, the parasite manipulates the grasshopper's behaviour to seek water and plunge into it, drowning itself in the process. As this happens the adult worm, which can be four times larger than the host, slowly undulates out of the former carrier into the water to seek a mate.

Image - the parasitic worm leaving the host to live the adult life cycle stage in the water.

(4/4) MALE MANIPULATION - Sacculina and the crab.

Sacculina is a barnacle that uses crabs as a host. As larvae, the barnacles are free-swimming but as adults if the females manage to land on a host crab, they inject their soft body into the crab as they free themselves from their shell. The parasite then develops, forming a sac on the underside of the crab, in a position where the crab's eggs are usually incubated. Whereas this effectively sterilises the crab, it still grooms and ventilates the barnacle's fertilised eggs as if they were their own. In addition, the crab can no longer moult it's shell but focuses on eating, obtaining resources for itself and the parasites. What’s stranger still is that if the barnacle has infected a male crab, then chemical changes occur which alter the crab physically and behaviourally to more reflect the female sex. Thus increasing the chances of survival of the fertilised eggs of the barnacle.

Image - the sac formed from the barnacle can be seen on the underside of the crab where it's own eggs would usually develop.