They aren’t as sexy as vampires, but roughly 40 percent of species on Earth live on the flesh, blood, and brains of other species. They’re parasites, and where vampires have a monotonous penchant for making their victims wander around with hollow eyes and prominent canines, parasites are highly imaginative in the ways they turn their hosts into instruments of their will.
The classic example is a parasitic fluke that infects a land snail, causing the snail to cough up slime balls, which deliver the fluke to an ant. But the ant is a way station en route to the fluke’s ultimate destination inside a sheep. So the fluke induces the ant to climb up on the tip of a blade of grass—the opposite of its normal instinct for self-preservation—and wait till a grazing sheep comes along to gobble it up along with the grass. The parasite then reaches its adult life as a fluke in the sheep’s liver. After it mates there, its eggs find their way back to other snails by way of the sheep’s droppings.
This is the strange circle of life, and since the discovery of that bizarre strategy in the 1950s, researchers have documented hundreds of other such parasite-host associations, in every animal phylum. For instance, a South American ant, normally black, sometimes develops a bulbous, bright red abdomen and then climbs up to assume the position, abdomen skyward, among the similarly colored fruit on a berry bush. The ant is mimicking a berry under orders from a nematode parasite, which is intent on achieving its destiny in the gut of a berry-eating bird.
Biologists are of course fascinated and regularly reveal intricate new parasite career plans. Thus a new study in Animal Behaviour describes a solitary fly in Virginia that ambushes a worker bumblebee as it forages among the flowers. Both fall to the ground. The fly (a conopid fly also known as “the thick-headed fly”) then uses can opener–like extrusions on its abdomen to shove apart the segments of the bee’s carapace and fire an egg into its abdomen. The bee soon recovers and Read the rest of this entry »