Despite practically one year’s worth of posts about parasite ecology, this blog has never characterized the term ‘parasite.’ D’oh! You can think, “Pft, the definition is obvious!” yet actually, that isn’t, and it no without controversy, either. I’m going come talk around a bunch of varieties of natural enemy, and then I’ll present a really good dichotomous vital at the end.

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Let’s begin with predators. Prefer parasites, predators space organisms that acquire power by acquisition that power from other organisms. Therefore, we have a connection that positive affects one organism (the predator) and also negatively influence the various other organism (the prey). Predators have actually these necessary characteristics:

1) One predator eats lot of prey throughout the predator’s lifetime.

2) Predators have tendency to be bigger than their prey.

3) Predators often tend to death their prey.


You’ll an alert that I said that predators “tend to” be bigger 보다 their prey and “tend to” death their prey. They don’t always! A very an excellent example of this is a vampire bat the takes blood meals indigenous cows. A solitary vampire bat will take blood meals from multiple cows throughout its lifetime. That is eating multiple prey, therefore, the is a predator. Yet it doesn’t kill the cows, and also it no bigger 보다 them. That a micropredator.


Parasites are different from predators due to the fact that parasites just take resources from one host, conversely, predators eat countless prey. A great example the this is the trematode parasite Schistosoma mansoni. An adult schistosome parasite stays inside of just one human being host. That is never going come crawl out and go epidemic a various human.

You could be thinking, “Waaaaait… Schistosoma mansoni has a facility life cycle! it infects humans and also snails! That’s two hosts!” Yep. Yet the rule is the parasites only infect one hold during each stage that the life cycle. One human. One snail.

Here are some various other common features of parasites:

1) castle are smaller sized than their hosts.

2) they don’t normally kill your hosts.*

Ok, so, the killing little bit is confusing and also wishywashy. Okay come earlier to it below.


Like a parasite, a parasitoid infects simply one host per life stage. But parasitoids constantly kill your hosts.

Parasite vs. Parasitoid:

So, those the difference in between a parasite and a parasitoid? If you’re about to take it an exam or something and also you want a rapid answer, say that parasitoids always kill their hosts and parasites don’t generally kill your hosts. You’ll uncover that in many introductory ecology textbooks.

In practice, us don’t really usage that definition. The term parasitoid is usually used to specific insects that have actually free-living adult stages that lay eggs within a host, and the eggs walk on come parasitize and also eventually death the host.

There are countless “parasites” that always kill your hosts, and also we still speak to them parasites and not parasitoids. Why, Scientists? Why execute you do this thing? Well, it just doesn’t make feeling to have actually a preeminence that states that parasites don’t death their hosts. For instance, if a parasite (say an acanthocephalan) in an intermediate hold (a pillbug) renders the host an ext likely to get consumed by the next host (a bird) in the life cycle, then the parasite is regularly the reason of the host’s death. Those kinds of helminth are referred to as trophically-transmitted parasites.

A really Nice Dichotomous Guide:

Lafferty and also Kuris (2002) came up with a really nice dichotomous crucial for classifying organic enemies. Lock used 4 dichotomies, however I’m only going to usage the very first three:

1. “Does the opponent attack an ext than one victim?”

2. “Does the enemy remove victim fitness?” (‘Eliminating fitness’ could be killing the victim or sterilizing the victim so the it cannot reproduce.)

3. “Does the opponent require the fatality of the victim?”

Figure adapted from Lafferty and also Kuris (2002) – link below.

See more: What Does Sub Mean In Medical Terms ? Sub Definition & Meaning

You might remember from one of my previous write-ups that we have tendency to division parasites into microparasites and macroparasites. Together I explained in the post, because that microparasites, we care about presence/absence the infection, and for macroparasites, us care about intensity the infection. The fourth dichotomy offered by Lafferty and Kuris (2002) is “does the enemy cause intensity-dependent pathology?” They incorporate the 4th dichotomy in your figure. It’s yes, really useful, but I didn’t incorporate it here to stop confusion. Click the PDF link listed below to check out their version.


Lafferty, K.D., and also A.M. Kuris. 2002. Trophic strategies, animal diversity and body size. TREE 17(11): 507-513. (Direct connect to PDF download)

Britt Koskella top top February 8, 2014 in ~ 8:41 am said:

Very quite post, and you room brave to effort to dichotomise. I tend to prevent it once possible! I regularly refer come bacteriophages together parasites, yet others refer to them as parasitoids (which ns don’t like because they are reproducing quite than simply occurring within their hosts) or predators (which ns don’t like due to the fact that of the one host preeminence you describe above).One question for girlfriend – over there are plenty of bacteria and fungi that develop spores that are just released at host fatality (for example, daphnia parasites) however are no trophically transmitted. Exactly how would friend classify these?

dinoverm ~ above February 8, 2014 at 7:45 pm said:

I found a more recent parasite category scheme by Poulin (2011) in breakthroughs in Parasitology. His category scheme is based upon the variety of hosts supplied per generation (i.e., facility life cycle or not) and also the variety of hosts offered per life stage, the effects on host fitness, and whether the hold dies. He ends up with 6 categories: parasitoid, castrator, directly-transmitted parasite, trophically-transmitted parasite, vectortransfer parasite, and micropredator. He clearly puts Cordyceps in the parasitoid group.