Parasitoid wasps are kind of a nightmarish bug: they lay eggs in their target, usually a caterpillar; the eggs hatch and the larvae grow inside the body of the target, feeding on non essential tissue so not to kill it, then they get out of the body of the caterpillar and make a cocoon in which they mutate into wasps, while the target caterpillar, still alive, has been hacked into protecting the cocoons from any aggressor, renouncing to feeding until the wasps come out and the caterpillar dies of starvation.

The fictional parasitoid wasp I am designing follows the same route, however

  • it is the size of a hornet and target primates, humans included.
  • The eggs are laid in 2-3 rounds, 20-30 eggs per round about 5 days apart form each other, in the same target.
  • An egg hatches in about 5 days and the resulting larva eats and grows for 3 weeks before emerging and building the cocoon, which will then be protected by the target until the adults come out after 2 more weeks.

From the moment the first egg is inoculated, the target starts feeling attracted by water until, when the first egg hatches, it does nothing more than settling around a water source (to prevent dying from dehydration).

The problem I am having is finding a suitable target tissue: I though about adipose deposits, but those are the first to be consumed when food intake stops.

Which tissue in a primate/human body can be consumed by the larvae without affecting the capability of the target in defending the cocoons? Survival of the target at the end of the whole process is not expected.

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    $\begingroup$ One question, how does the wasp track 'the same target' over days? As far as I am aware all parasitic organisms are more or less opportunistic, i.e they infect the suitable host they encounter. If your wasp is going to attack the same person/host two or three days in a row they will would have to be able to track/stalk them wherever they go over that time period. Which is kind of a hard ask for an insect and probably counter survival given any human will do it vastly ups it success rate if it just attacks whoever it can find. $\endgroup$
    – Mon
    Nov 6, 2021 at 2:40
  • $\begingroup$ @Mon changing the odor emitted by the target can make tracking it easier, topped with the push to stay around water sources $\endgroup$
    – L.Dutch
    Nov 6, 2021 at 4:52
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    $\begingroup$ Possibly, but water can be found in a tap, in a house, with lockable doors and windows. Plus humans are sentient, well at least sentient enough to realize they may have been 'impregnated' or whatever the correct term is as the symptoms begin to manifest themselves and therefore go to seek help. Animals won't/cant do that. I still see no reason for for the wasp to focus on an individual. it would be counter evolutionary. $\endgroup$
    – Mon
    Nov 6, 2021 at 9:36
  • $\begingroup$ isn't this just a variation of the bott fly? en.wikipedia.org/wiki/Botfly Similar egg count, parasitises mammals including humans and apes, the only part that isn't already covered by reality is the compulsion to be by water and the tracking of the person for repeated parasitising $\endgroup$ Nov 6, 2021 at 15:44
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    $\begingroup$ You do realize that parasitoid wasps always kill their prey (that's the definition of parasitoid) right? And thus, there is no strategy because you picked on the one species smart enough to fight back. $\endgroup$
    – Joshua
    Nov 6, 2021 at 23:51

6 Answers 6


Humans, as with all primates, are remarkably adept at scratching, self-and-social grooming. Any parasite that can be attacked from the surface, will be.

A parasite needs to either dig deep enough so that normal scratching and grooming cannot dislodge it, or present such a small irritation factor (and be not obviously visible) so as to ensure the parasite's survival.

Typical successful parasites on humans:

  • Fleas: small enough to not be obvious, mobile enough to evade removal, and low enough irritant value to not instigate massive retaliation. Not a god match for your flesh-devouring Wasp larvae.
  • Tapeworm: fully internal thus not reachable by any manipulation. Additionally, it does very little damage to the host, ensuring host survival thus longterm parasite survival. Again, not a very good match for flesheating worms.

Your parasite has to enter via the a skin puncture, as it is deposited by a wasp.
Make the egg and larvae secrete a local anesthetic which nullifies the pain and irritation factor. Maybe some anti-inflammatory and antibiotic secretions too, to massively reduce its visible effect on the host. No pain, no swelling, no itching.

Make the larvae burrow deep into muscle tissue, latch on to an artery, and sip the sweet nectar from their host's bloodstream. This should cause minimal irritation, only very minor muscle damage and not excessively weaken the host, while providing ample nutrition (and waste removal) for the larvae. It also provides a handy pathway to fiddling with the host's internal chemistry, providing all sorts of psycho-control opportunities if your larvae is "smart" enough for that.

And please tell me what planet you are releasing this terror upon,. so I can move to a galaxy far,far away. It is at the very minimum a horrid incurable wasting disease, and could very easily be the root of a classic Zombie Apocalypse.

  • 5
    $\begingroup$ I thought a larva feeding inside one's body was already a nightmare, and you managed to make it even more nightmarish by merging it with a leech... $\endgroup$
    – L.Dutch
    Nov 5, 2021 at 9:49
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    $\begingroup$ In a way, Bot flies do this. However, they can be very irritating, itchy and painful with plenty of indications that they are there. They are successfully because, once they infect a host, they are fairly difficult to remove safely. It may be difficult for the larva to keep secreting a numbing agent to hide its presence, as its more likely to secrete an anti-coagulant to keep the food coming its way. $\endgroup$
    – Sonvar
    Nov 5, 2021 at 13:52
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    $\begingroup$ @Sonvar I've seen videos of bot flies larvae being removed from humans (f*%k you, YouTube's algorithm) and it's hard for me to 1. believe those things managed to grow to such size prior to any action taken by the "victim" to remove them and 2. imagine how painful, irritating and uncomfortably has to be to have one/some of those things inside $\endgroup$
    – Josh Part
    Nov 5, 2021 at 19:32
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    $\begingroup$ initially, you do not feel them. the more successful flies will attack in areas that the host cant see, such as the butt of animals (they are attracted to urine and feces covered fur). Once they are below the dermis level, you do not have pain receptors that deep, so you do not feel them initially. Once the irritation and pain starts, they are of a size were removal can actually be hazardous to the host. $\endgroup$
    – Sonvar
    Nov 5, 2021 at 19:46
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    $\begingroup$ And please tell me what planet you are releasing this terror upon. I believe that these were first found on LV-426. $\endgroup$
    – dotancohen
    Nov 7, 2021 at 10:51

First things first: half of what you want already exists. There is a condition called myiasis which is caused by some kinds of flies laying eggs in the human skin. From there the larvae hatch in as little time as eight hours and then burrow deeper into subcutaneous issue. The flies that cause this will usually target the buttocks of livestock, but when it comes tohumams they are not picky about specific body parts. They will exploit any sores they can find though. I have personally seen surgery done to remove larvae from a woman's scalp.

Worst thing is, since the flies are able to lay their eggs on an open wound, people may get myiasis without noticing it if they have an untreated wound and are distracted. If your wasp can facultatively do this, it will be that more dangerous.

If the wasp must pierce through, then soft areas will be preferred. Ask any nurse about the best places to innoculate someone with a vaccine, and you may learn that after the arm another common target is the bum. The belly is also a possibility - it used to be that people in risk of rabies would get their shots there. Consider also the armpits, the space between ribs, and a little spot right above the colllarbone.

That said, the preference for damp places is a matter of also injecting some venom along with the eggs. Many kinds of substances will cause a person to feel thirst. If the wasp also injects THC, the active drug in cannabis, the victim may get the munchies which is favourable to keeping them distracted and fed, thus leading to a higher ratio of larvae making it to adulthood. Maybe the wasp feeds on cannabis or other poisonous plants or fungi and hyperconcentrates the dosage in their ovipositor.

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    $\begingroup$ @L.Dutch -- It may not be quite what you're looking for, but the gist is "humans make excellent nurseries, no matter where you lay your eggs". $\endgroup$
    – elemtilas
    Nov 5, 2021 at 12:01
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    $\begingroup$ @TheSquare-CubeLaw -- Between the ribs and the suprasternal notch are the worst places for injections of any kind. At least not without image guidance! A wasp sting, of course, is a different matter! $\endgroup$
    – elemtilas
    Nov 5, 2021 at 12:06
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    $\begingroup$ /The bwlly is also a possibility/ - but only in Wales. $\endgroup$
    – Willk
    Nov 5, 2021 at 19:01
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    $\begingroup$ @L.Dutch There are a number of cases of botflies even burrowing into the scalp to metamorphose, where there is next to no edible tissue. Your wasp can seemingly survive just about anywhere, so long as your parasitoid isn't extremely large. $\endgroup$ Nov 5, 2021 at 20:00
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    $\begingroup$ The flies seem to be opportunistic -- they are always around and looking for good places to lay eggs. Good hygiene can defeat them. The wasps seem meant to be more like predators -- find just any caterpillar, or human, "capture" them, and do their rounds of eggs. $\endgroup$ Nov 5, 2021 at 21:50

The Brain:

And the worms ate into his brain.

Wasps that enslave other insects are able to perform a simple form of brain surgery on cockroaches to assure they are compliant. If you want to control a mammal's behavior, there's no better target than the central nervous system. While A wasp can't pierce the skull, there's no reason that eggs injected into the blood stream of a primate can't migrate to the brain and do the work directly there.

Anyone who's had a brain tumor can (hopefully) tell you they can take up a large part of the skull and still have a semi-functional person. A primate driven by larvae to perform instinct-like behavior doesn't need to last forever, just long enough to release its hornets.

But as was pointed out, the larvae can subsist perfectly well on blood, so they don't need to eat the entire brain, just make a big enough compartment (similar to a tumor) for the larvae to grow. If the primate survives the initial infection process, they could continue growing larvae as long as their body could survive.

My suggestion is that the hornet crawls into the ear, then injects the primate with eggs. The eggs either migrate through the blood (like encysting tapeworms) or hatch in the ear and burrow into the brain and make a space for larvae to live (ideal, since most insects would need a hole to obtain oxygen for respiration). Larvae in the brain can potentially control any behavior you want - Rabies is known to make people repelled by water, and attraction to water is known for earwigs. Diseases can make animals engage in risky behavior so as to increase the odds of predation (and thus allowing the next step in a life cycle) so the infected might seek out areas where the hornets are prevalent to allow repeated infection. The larvae may even stimulate the pleasure centers, so the primates are deliriously happy about being infected and don't seek treatment or help. The larvae could suppress hunger (allowing the person to support more larvae till the starve) or cause ravenous hunger (so the host does anything to keep eating, allowing them to continue growing larvae). Then they could either seek out other primates to increase the odds of cross-infection, OR avoid other primates to reduce the odds of getting help. These behaviors could be controlled by paranoia or aggression.

The larvae hatch and crawl out of the ear a new hornet.

  • 1
    $\begingroup$ I think they should get to the brain via the eyes rather than the ears (and then via the ocular nerve) for extra squick. The first symptom could be hallucinations. $\endgroup$
    – abligh
    Nov 6, 2021 at 4:45
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    $\begingroup$ @abligh The eyes could work, but primates are super-primed to protect their eyes. A hornet could crawl into an ear and even if the person realized what was happening, the hornet might be protected long enough to lay eggs. Plus a primate losing hearing in one ear is less inconvenienced than one blind in one eye. But yes, hornets crawling out of an open eye socket would be really horrifying. $\endgroup$
    – DWKraus
    Nov 6, 2021 at 22:05
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    $\begingroup$ Parasitic Brain Infections are extraordinarily rare, due to the blood brain barrier. $\endgroup$
    – dotancohen
    Nov 7, 2021 at 10:53
  • $\begingroup$ @dotancohen That's another reason that larvae eating their way in through the ear makes the most sense. $\endgroup$
    – DWKraus
    Nov 7, 2021 at 17:46


nasal bots

enter image description here sinuses

https://www.agric.wa.gov.au/livestock-parasites/nasal-bots-sheep https://teachmeanatomy.info/head/organs/the-nose/

Depicted: nasal botfly maggot in sheep sinus, human sinuses.

The thing about insects: they are not worms. They cannot oxygenate in a liquid environment like helminths. They have to breathe air. That limits where they can live as parasites. The deep tissues do not have free air and larvae will suffocate.

The sinuses work fine. They are aerated. They are vascular and the larvae would have loads of blood and protein rich secretions to eat. This is how sheep botflies do it. Humans can be infected with sinus botflies too.

The sinuses also have access to the CNS via the cribriform plate.



The larvae in the sinuses give off chemicals which diffuse into the brain and reduce motivation and causes these people to sleep by the river.

I think I like about this scenario is that it might not be fatal. The infected would sit and sleep along the river banks with faces swollen and their noses dripping purulent stuff. Some might lose an eye, or both. But they have family and the family knows what is up. People take shifts watching over the infected at night. They bring them food. They keep them warm. They fend off predators.

The larvae hatch in about a month and fly off, then the people wake up. If you survive this infection you are resistant to a second infection both immunologically and because your sinuses are so scarred. Survivors can resume a normal life. More or less normal - it is not hard to tell who they are, because they do not look the same afterwards.

I envision the healer with her jar of these larvae, each with a thread tied around it. She puts some in the nose of the sick person and over the next few days he settles down and becomes somnolent and uncaring. Then she can do the surgery he needs. Once she is done, she pulls the larvae out by the threads and saves them for the next patient.


Leg Muscles

A healthy human has a lot of muscle on their lower body.

A human laying next to a water source while being consumed from the inside does not need legs.

Therefore, this (horrifying) parasite targets leg muscles, possibly extending to core and back muscles near the end.

Predator Defense

Primates are pretty good at hitting things with sticks and rocks. A primate without legs is significantly less maneuverable, but is still dangerous to provoke.

If the parasitic wasp remains near its victim, it could aid in its defense, since it is a highly mobile attacker.

Even if the primate is killed, predators tend to prioritize high value parts like organs, and are likely to save the already necrotic leg muscles for a time of great need. There's a good chance that some of the larva will survive to their horrifying adult phase.


The back of the mouth or throat

Some advantages of this location are:

  • Soft, easily penetrable tissue
  • Plenty of moisture
  • Steady supply of oxygen
  • Whatever the host eats and drinks can supplement the larvae's diet
  • Depending on where they embed, larvae may be difficult to see and difficult to reach with fingers and tools
  • Larvae may retaliate against removal attempts by triggering a violent gag reflex and vomiting
  • Easy access to nasal cavity, which is apparently a great place to deliver brain-altering drugs
  • Exhaled carbon dioxide could help adult parasites track hosts and locate ports of entry (this is one of the ways that mosquitos find us).

Some disadvantages are:

  • Tissues are easily irritated and will likely require injection of anesthetic and anti-inflammatory agents
  • Lots of mucus-and-saliva-filled crevices that small insects could get trapped in
  • Egg implantation attempts will only go unnoticed if target is asleep
  • Oral entry/exit limits target availability to those who sleep with mouth open
  • Nasal entry/exit limits allowable size of adult parasite

While I'm not aware of any real-life macroscopic parasites that specifically target the human throat, there are several species of worm that may take up residence there after being ingested by the host (e.g. Clinostomum complanatum and Pseudoterranova azarasi).

However, the main inspiration for this answer was the tongue-eating louse (Cymothoa exigua), a horrifying parasitic isopod that clamps onto the tongue of a fish and eventually replaces it, becoming the fish's new tongue. Obviously, this approach wouldn't work on animals that can dig things out of their mouths with fingers and tools, so some reimagining will be required. But the "ewww" factor might make it worthwhile. How creepy would it be if someone yawned in your direction, and you thought you spotted the glint of beady little bug-eyes looking back at you from dark cavity of their mouth?

Cymothoa exigua (tongue louse)Pair of tongue liceTongue lice outside fish

Another inspiration was the mythology about creepy crawlies entering people's mouths while they sleep. Typically presented in the form of a statistic to give it that "factual" quality (e.g. "on average, you swallow 8 spiders in your sleep each year"), some variation has probably been heard by just about everyone. Even though I know it's a myth, the thought of it does occasionally drive me to roll onto my side at night. I suspect that's the sort of feeling the OP is aiming for.


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