Why you should care about parasites

Why you should care about parasites


Parasites don’t make the cut on most of
our favorite creature lists but maybe that’s because we simply don’t know the
crucial and surprising roles they play in the ecosystems all around us. These
endangered Japanese trout rely on an unlikely ally to survive: Tiny parasitic
worms that need to make their way from land to water in order to mate. To get
there, the worm infects crickets and prompts them to fling themselves into
streams. The sacrifice delivers the worm to water, and the unlucky crickets
provide up to sixty percent of the endangered fishes food supply. Parasites
like this one may be critical to the functioning of many ecosystems, but they
have historically been left out of the maps scientists create to help understand
the flow of energy through a habitat. Ecologists have built hundreds of food webs and they
haven’t put parasites in them — and what we’ve lost from that is the ability to even
think about parasites and their roles in ecology. Take the African Savanna where
— almost any child will tell you — lions are king. Normally we think the lions are untouchable, but in
fact they have all these ticks, fleas, protozoans, 31 species of tapeworms and
nematodes and trematodes and on and on. And, in fact, there’s more things
eating lions than things that lions eat. Though we rarely see them, parasites may
make up as many as half of all known species. The roles they play are not
always what you’d expect. In the salt marshes of Southern California, for
example, a trematode worm moves from one host to another as it develops, living in
snails as larvae, and reproducing only in the gut of shorebirds. It makes the
transition through an unusual route: The brain of a fish. Fish with parasites on
the brain are more likely to flash their silvery bellies toward the sky — a beacon
to hungry birds overhead. The result: Infected fish are up to 30 times more
likely to get caught, delivering the parasite to its final avian home.
Parasites may regulate population numbers by feeding on their host species
and competing with others for food. In the few cases where parasites have been
added to food webs, the enhanced complexity is obvious. This is a food web
that we constructed for Estero de Punta Banda, which is an estuary in Baja
California, Mexico. Here each ball represents a species and each gray line
connects a consumer to the species that it eats. The species down at the bottom
are the plants, and they’re in green, and then all the free living animals are in
red. We can also see that there are trophic levels so we go from plants to herbivores and then to different levels of predation as we move from the
bottom to the top. The next step, then, is to add parasites and see what changes.
You can see that food web is a lot taller now with the parasites, because of
the additional trophic levels that parasites provide. As scientists work to
understand how parasites fit into ecology, some have even begun to talk
about parasite conservation, arguing that losing certain parasites might have
ramifications we are just beginning to understand. Some parasites even benefit
humans directly. If you’re into eating organic foods,
you can thank lots of parasites that take out some of the insect pests that
reduce crop yields, and we use those instead of pesticides arguably to our better health.
Parasites may also be worth preserving because they’re just really cool. We may
never love the nine meter worm that infects sperm whales as much as we love its
hosts, but you can’t deny that it’s an impressive specimen.
And it’s hard not to be left speechless by the marine louse that gobbles up a
fish’s tongue, only to replace the organ with its own body. A lot of them are
just fascinating examples of evolutionary strategies, some of which
are sort of, you know, disgusting perhaps but certainly sinister and fascinating
all the same.

1 thought on “Why you should care about parasites”

Leave a Reply

Your email address will not be published. Required fields are marked *