MEDIA, Pennsylvania (WPVI) -- If you go into Ridley Creek State Park and hop on the White Trail, then take just a short walk up a hill, you'll start to smell it.
Hiker Gus Desimone of West Chester said, "I don't know how to describe it, it just smells bad."
Then you see it - a colony of the invasive Spotted Lanternflies.
When we came upon them, they were feasting on the sap of their favorite tree called the Tree of Heaven or Chinese sumac, which is also an invasive species.
Mike Delozier of Media said, "They're definitely a little prehistoric-looking, a little weird."
Along with the stench, the flies leave behind a black kind of slime which is actually sap mixed with their excrement.
Desimone said, "It's slimy. They're everywhere. Luckily, they didn't swarm me when they came over here."
So why are they a threat?
Though aesthetically beautiful, they've been known to move from the "Tree of Heaven" to native maple trees and grape vines. That could mean serious damage for the maple and wine industries.
Since they're so new to the area, different ways to kill them are just being trialed.
Park officials said they're considering using insecticide once they've gathered together in a large group.
But the flies jump and they're hard to catch.
Other methods being tested are to coat insecticide on the trees they feast on so they'll ingest the poison or to simply cut down their food source.
However, at this point, there's no clear path to stopping the flies.
There are also no known predators for them here either.
"I remember what it was like with that stink bug invasion. Stink bugs seemed to have disappeared so maybe these will too," Elsa Rapp of Newtown Square said.
Park officials said the one way you can help stop Lanternflies or any invasive species is to only plant native species on your property. That way these kind of bugs won't have as much food to thrive on.
More Information: Spotted Lanternfly
Spotted Lanternfly spotted at Ridley Creek State Park