Scientists have identified two previously unknown species of parasitic wasps spreading across the US, from New York to the Pacific coast. 

Hailing from Europe, these tiny predators deposit their eggs inside oak galls. Their larvae then slowly feast on the bodies of native oak gall wasps before they mature and emerge as adults.

The adult female wasp injects one or more eggs into or onto the body of a host insect, in this case, oak gall wasp larvae inside galls. 

Upon hatching, the larvae consume the non-vital tissues first to keep the host alive for as long as possible, ensuring a consistent supply of fresh food.

Over days to weeks, the larva progressively eats the host’s tissues, eventually consuming it entirely. 

Experts suggested the parasitic wasps came to the US through imported oak trees or through planes before exploding in population.

While there is no threat to humans, scientists warned that the wasps could upheave America’s ecosystem.

These predators might not only target oak gall wasps but could also vie with or displace native parasitic wasps. These native species are essential for controlling insect populations, maintaining ecological balance, and supporting biodiversity.

Scientists have discovered two species of an invasive wasp that feasts on the bodies of native wasp

Originally from Europe, these tiny predators lay their eggs inside oak galls (pictured), where their larvae gradually consume the bodies of native oak gall wasps before emerging as adults

Both species, called Bootanomyia dorsalis, were previously thought to be one species, but genetic data show there are actually two: B. dorsalis sp. 1 and B. dorsalis sp. 2.

The first was identified in New York, and the other was found in oak galls in Washington, Oregon and British Columbia.

The New York species showed more genetic diversity, meaning it may have been introduced multiple times.

While the wasp on the west coast had very little genetic variation, suggesting it came from a small founding population.

These wasps only attack oak galls, so they may have arrived alongside European oak trees that were planted in North America, the researchers said.

Species like English oak and Turkey oak were brought to the US centuries ago, making it possible for adult wasps to hitchhike on cargo or planes, as they can live up to 27 days. 

Kirsten Prior, a biological sciences professor at Binghamton University, said: ‘We did find that they can parasitize multiple oak gall wasp species and that they can spread, given that we know that the population in the west likely spread across regions and host species from a localized small introduction.

‘They could be affecting populations of native oak gall wasp species or other native parasites of oak gall wasps.’ 

The adult female wasp injects one or more eggs into or onto the body of a host insect, in this case, oak gall wasp larvae inside galls

The team warned that the Pacific coast population is already widespread, and reports suggested the New York population may also be spreading. 

‘This finding of multiple introductions into the North American oak gall system – one of them apparently quite well-established across the Pacific coast – makes it reasonable to presume that the portcullis has been raised for parasitic wasp invasions, as it has been for so many other insects,’ the study reads.

North America has around 90 different species of oak trees, and around 800 species of oak gall wasps that live upon them. 

However, the introduction of two parasitic wasp species, including a previously unknown one, could pose serious risks, warned Prior.

‘We found that these wasps can parasitize multiple oak gall wasp species and that they are capable of spreading,’ Prior said. 

‘They could be affecting populations of native oak gall wasps or other native parasitic wasps.’ 

Prior cautioned that the newcomers could decimate native gall wasp populations, either by direct parasitism or by outcompeting them for survival. 

Disrupted Ecosystems Although tiny, oak gall wasps play a surprisingly important role in forests. 

Their galls provide homes and food for fungi, beetles, spiders, and even small vertebrates. 

That means any decline in gall wasps could trigger ripple effects throughout the forest food chain, affecting countless other species that rely on these miniature habitats.