Parasitic ‘horror wasp’ that grows inside living flies discovered in US

Scientists in Mississippi have discovered a new species of parasitoid wasp that matures inside living adult fruit flies before bursting out, much like a scene from the Alien films. This newly found wasp, named Syntretus perlmani, is the first known to infect adult fruit flies, a stark contrast to related wasp species that usually target the larvae and pupae stages of flies.

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The research, led by Logan Moore during his doctoral studies at Mississippi State University, was published in the journal Nature on September 11. The wasp species was uncovered by chance while the team was collecting fruit flies in their backyards.

Uncovering the deadly parasitoid

In an interview with Live Science, Moore explained that female S. perlmani wasps use a specialised organ called an ovipositor to inject eggs directly into the abdomen of adult fruit flies. Over the next 18 days, the eggs develop into wasp larvae, slowly growing inside the host until they eventually kill the fly by emerging out of its body.

Moore described the chilling process: "It will effectively emerge out of the side of the fly, and just to add an additional layer of horror, the fly will normally remain alive for several hours after that."

The discovery occurred in March 2023 when the team was examining fruit flies for parasitic worms and noticed a strange wasp larva inside one of the flies. At first, they dismissed the finding as a one-off anomaly, but further investigation revealed more larvae. The team later confirmed their discovery by rearing the wasps in a lab and analysing their DNA.

First wasp species to target adult fruit flies

What sets S. perlmani apart from other parasitoid wasps is its ability to infect adult flies rather than their more vulnerable juvenile stages. Typically, insects are more susceptible to infection as larvae or pupae because they lack a protective exoskeleton and cannot escape easily. This makes S. perlmani a unique and surprising discovery.

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"This is all around us, infecting one of the most well-studied animals on the planet," Moore said. "It just leaves you wondering what else is out there on our doormat right now."

The research team found evidence of the wasp across the eastern United States, including Mississippi, Alabama, and North Carolina. Additionally, genetic data revealed the wasp’s presence in Drosophila melanogaster, a commonly studied fruit fly species.

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