Fungus spores attach themselves to an insect, disorientate it so it walks up a branch, and then a mushroom grows out of the back of it's head. Each fungus specialises in just one species. It is noted that they effectively control the growth of insect colonies, so none get too large. A species of ant has adapted, and the workers will take any infected ant far away from the colony (the mushroom explosion sprays spores everywhere). Should a variant begin to specialise in humans, perhaps we could modify La Princesse to carry people away from densely populated areas.
I guess Shyamalan has also been watching Planet Earth. Although he missed a trick not having a big mushroom explode out the back of Mark Wahlberg's head.