The most disturbing stories begin not on a dark and stormy night, but with the phrase: “it was a warm, sunny day in a flower garden.” While humans admire the smells and colors of spring, horrific scenes of torture, attack and hijacking may be taking place.
The most brutal tales of body snatching are not in the far corners of the exotic world, but can be found right here at home in the Chesapeake.
Caterpillars seem like harmless little creatures just munching away on leaves. But unbeknownst to many, they play host to one of nature’s most bizarre parasites – wasps that lay eggs inside living caterpillars.
These wasps are known as ‘parasitoid’ wasps, and they have evolved an astonishingly macabre reproductive strategy. The female wasp will inject her eggs directly inside the body of a living caterpillar. There, the wasp larvae will hatch and begin feeding on the caterpillar, absorbing its body fluids while avoiding the vital organs to keep the host alive.
After maturing inside the caterpillar, the larvae will suddenly all erupt out of the caterpillar’s body in a horrific fashion to spin their cocoons nearby. Incredibly, the caterpillar survives this ordeal, only to then be mind-controlled by the parasitoid larvae to defend them from predators. The caterpillar stops eating and neglects its own wellbeing, instead standing sentry and lashing out against any insects that get near the pupating wasps. Not exactly normal behavior for a vegetarian!
Eventually the wasps will emerge from their cocoons as adults and fly away, leaving the caterpillar to die of starvation. This extraordinary lifecycle demonstrates the astounding adaptations parasites can evolve to maximize their survival and reproduction.
Why Do Wasps Parasitize Caterpillars?
Parasitoid wasps like those in the genus Glyptapanteles reproduce by laying their eggs inside living caterpillars for a gruesome but practical reason – it gives their offspring a much better chance at survival. If the larvae had to develop exposed to the elements, they would be much more vulnerable to predators and parasites.
By staying inside the protective bodies of caterpillars, the larvae are sheltered with a ready food source and can mature safely before making their rapid escape. The caterpillar hosts also supply useful camouflage and defense after the larvae burst out. Overall, this strategy greatly improves the odds of the wasp larvae surviving to adulthood.
How Do the Wasps Parasitize Caterpillars?
Female parasitoid wasps have evolved highly specialized ovipositors to inject eggs through the skin and into the bodies of caterpillar hosts. Depending on the species, they may lay just a single egg per caterpillar or dozens at a time.
The larvae hatch inside the caterpillar where they begin consuming body fluids, molting and growing through several stages. The caterpillar goes about life as normal, showing no ill effects despite the parasites developing within.
Finally the mature larvae erupt en masse out of the caterpillar’s body in a violent and rapid escape. They immediately begin spinning silk cocoons nearby where they pupate. Amazingly, the caterpillar survives this traumatic escape and then becomes mind-controlled by the parasitoid larvae to stand guard over the vulnerable pupae.
How Does the Mind Control Work?
The exact mechanism of the mind control remains a mystery. But researchers found that some larvae actually remain inside the caterpillar for several days after the escape event to manipulate the host’s behavior chemically. This is an incredible adaptation since these remaining larvae sacrifice themselves so their siblings can benefit from the caterpillar’s protection.
Defense Mechanisms of Caterpillars
Caterpillars aren’t entirely defenseless against these attacks. They have evolved various strategies to deter parasitoid wasps:
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Bristly hairs – Coarse uncomfortable hairs make it harder for wasps to pounce on them
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Venom – Toxins collected from host plants can paralyze small predators
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Barbed hairs – Get trapped in the wasp’s body upon contact
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Moving in groups – Form long processions to distract and evade wasps
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Hiding places – Using silk to build shelters out of leaves
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Camouflage – Blending in with leaves through coloration
Remarkable Examples of Parasitoid Wasps
There are thousands of parasitoid wasp species with extraordinary and often grisly lifecycles. Here are some of the most bizarre examples:
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Glyptapanteles – Injects up to 80 eggs into a caterpillar which it then guards while pupating
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Cotesia congregata – Lays eggs in tobacco hornworms, becomes cannibalistic if no hosts are found
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Cystomastacoides kiddo – Named after the Beatrix Kiddo Kill Bill character; paralyzes moth caterpillars from inside
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Netelia producta – Lays eggs on top of a caterpillar’s head and stacks them in visible brown columns
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Theronia circumflexum – Favoring pine hawk moth caterpillars; has a distinct orange and black elongated body
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Ichneumon eumerus – Enters ant nests to target specific caterpillars, sprays ants with chemicals to fight each other
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Microplitis croceipes – Lays just one egg per caterpillar; attracted to feces odor of hosts
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Agrypon flaveolatum – Used to control destructive winter moth caterpillars in North America
This bizarre method of reproduction demonstrates how far evolution will go to ensure the propagation of genes. By turning their prey into clones of themselves, bodyguards and eventual food sources, parasitoid wasps have become masters of survival through the truly macabre.
Ladybug parasite The parasitic braconid wasp, Dinocampus coccinellae, reproduces by injecting eggs into a ladybug. (Photo by coniferconifer/Flickr)
Have you ever seen a ladybug holding a puffball? It isn’t nearly as innocent as it appears. The parasitic braconid wasp, Dinocampus coccinellae, turns a ladybug into a paralyzed incubator, food source and bodyguard.
The wasp inserts an egg into the underbelly of the ladybug with a single sting. The wasp larva, in a safe and protected home, feasts on the ladybug’s insides.
When the larvae is ready to hatch, it employs a neurological weapon: a virus. The virus was injected into the ladybug at the same time as the egg and while it grew, the virus did, too. The virus builds up in the brain cells, and will burst open at about the same time that the wasp larva chews its way through the ladybugs insides and bursts out its stomach.
Affected both physically and neurologically by the wasp and virus, the ladybug is paralyzed. It can only twitch as the wasp larva spins a puffy cocoon on the belly of the ladybug.
The ladybug then “guards” this puffy cocoon while it is vulnerable. The ladybug’s bright red back and occasional twitching keep predators away. The adult wasp emerges from the puffy cocoon about a week later.
Most of the ladybugs die from this encounter, though some are able to recover and survive. The quality of remaining life for the ladybugs that survive or the lasting effects from the experience are not well understood by scientists.
Wasps are important biological controls, which means they keep various caterpillars, worms, spiders and other insects that eat plants in check. If you’re a fan of herbs, lush gardens or fruits and vegetables, you should be a fan of wasps. The chilling factor comes in if you look too closely at just how wasps like the braconid keep a cap on caterpillars.
A braconid wasp (Braconidae) will descend on a caterpillar–say, a hornworm snacking on a tomato– and slit into its soft caterpillar body. The female wasp injects the caterpillar with her eggs and a virus, which shuts down the caterpillar’s ability to defend against these intruders.
The wasp larvae deposited into the caterpillar body begin to grow beneath the surface, snacking on the caterpillar innards.
When they’re ready, 80 or so larvae will chew out of the caterpillar’s body with their tiny razor teeth. Each small larva spins a cocoon, covering the caterpillar in little white puffy rice grains. The adult wasp will emerge from the cocoon by cutting a trapdoor cap into the cocoon, then fly away in search of its own fresh host.
Emerald cockroach wasp The emerald cockroach wasp houses its young in the body of a living cockroach. (Photo by Sharadpunita/Wikimedia Commons)
The American cockroach (Ampulex compressa) can withstand high doses of radiation, survive underwater for up to 30 minutes and can safely consume almost anything without detrimental effects. It has been on the earth since before the time of the dinosaurs and appears virtually indestructible.
Enter the emerald cockroach wasp: a beautiful, iridescent and gory killer. Instead of spinning a soft home like other insects or finding a nice secluded log to house its young, the emerald wasp picks the body of a living cockroach as its nursery.
Approaching the cockroach from the front, the wasp holds the roach’s head in both front legs the way one might console a loved one, then jabs its stinger into the roach’s brain. The injection paralyzes the roach, at which point the wasp takes the roach antennae in its mouth and leads it back like a dog on a leash to the wasp burrow.
Controlled and docile, the roach sits passively while the wasp creates a cage out of pebbbles around the roach.
After laying eggs in the roach’s stomach, the roach is eaten alive from the inside by wasp larvae. Once they’ve eaten their fill and grown up in the cockroach’s body cavity, adult wasps burst from the remains of the roach.
Body Invaders | National Geographic
FAQ
What kind of wasps lay eggs on hornworms?
Tomato hornworms are also parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae hatching from wasp eggs are laid on the hornworm. The wasp larvae feed on the inside of the hornworm until the wasp is ready to pupate.
Do wasps lay eggs in monarch caterpillars?
Both fly and wasp parasitoids lay their eggs on monarch larvae, but the most important larval parasitoid is probably a fly species in the family Tachinidae.
Do trichogramma wasps sting?
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Tiny and Harmless:Trichogramma wasps are extremely small, often less than half a millimeter in length, and are not known to sting or bite humans or other animals.
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Beneficial Control:They are used as a form of biological control, meaning they are used to control pests naturally by parasitizing their eggs.
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How they work:Female Trichogramma wasps lay their eggs inside the eggs of moths and caterpillars, and the Trichogramma larvae then develop inside the host egg, consuming it and preventing the moth or caterpillar from hatching.
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Not interested in humans:Trichogramma wasps are not interested in humans, so they do not sting or bite.
Are parasitic wasps harmful to plants?
No, parasitic wasps are not harmful to crops or beneficial insects. They are highly selective in their choice of host pests, ensuring that they primarily target harmful insects. This makes them a valuable addition to integrated pest management (IPM) strategies.