Another parasite of ants tells a similar story. In the tropical forests of South America, there lives a quite remarkable fungus. If a Carpenter ant (Camponotini) is unfortunate enough to eat spores of the fungus Ophiocordyceps unilateralis, those spores release chemicals into its brain altering its behaviour. The infected ant gives up its normal day-to-day activities and becomes a zombie. Defenseless against the fungus� tricks, the zombie ant leaves its nest, climbs the nearest plant and finds a suitable leaf, clamping its jaws down onto the stem. Here it remains, immobile, and completely powerless. Over the following hours and days, the fungus begins to sprout from the ant�s head, growing a tall stalk that, at its tip, eventually produces spores. These spores are carried away on the wind, ready to infect more innocent ants.
The zombie-ant fungus, as it�s affectionately known, was first discovered in 1865, but we now know there are at least ten closely related species of fungus, which infect different species of carpenter ant the world over. Eight new species have been discovered in the last decade4,5, and there may be many more yet undiscovered. However, researchers believe that one fungus species, Ophiocordyceps camponoti-novogranadensis, may not be zombifying ants for much longer. Found at high elevations, this fungus is under threat from climate change, which scientists believe the ants will be able to survive but the fungus may not4. Good news for the ants, perhaps, but for us yet more evidence of how climatic changes are disrupting species interactions.
All parasites must get from one host to another, but some species have highly complex life cycles with multiple hosts, magnifying the challenge of transmission. One of the most convoluted parasite lifecycles is seen in the lancet fluke (Dicrocoelium dendriticum), and this lifecycle calls for sophisticated host manipulation. During its life, the lancet fluke must move from its primary host (where it reproduces) in a cow (Bos taurus), through a snail (Cochlicopa lubrica) and finally an ant (Formica fusca). This amazing parasite has therefore evolved to infect three different hosts, and find a way from one to another.
Getting from the cow to the snail is quite easy; lancet fluke eggs exit the cow in its dung � a tasty snack if you�re a snail. Inside the snail, the flukes make their way to its respiratory system where they are eventually coughed up in a large ball of phlegm. This ball of fluke-infected mucus is just irresistible to the ants, which enthusiastically carry it back to their nest and consume it. But once infected with the lancet fluke, the ants start to act a little strangely. The following evening they leave the nest, climb to the top of a blade of grass and bite down. Here the ants remain, unflinching, until sunrise, when they return to the nest and act as though nothing ever happened. This ritual continues daily until one night, the selected blade of grass is eaten, completing the cycle and returning the flukes to their cow-shaped home, where they can reproduce once more.