The pesky horsetail plant was an ancient and large problem for all countries in the Southern Hemisphere, where it's a weed. In the Northern Hemisphere, it's a native.
It was believed the horsetail was first introduced in Whanganui.
Now in New Zealand's environment, the weed posed a threat to the river systems and roading corridors because of the aggregate industry.
All the metal and stone transferred to different locations, could transfer horsetail too.
The weed appeared to cause no damage to native flora, but was a major problem for farmers and their pasture.
"Because it is a mono-culture it is very chemical resistant and it will absolutely out compete pastures and crops when they are establishing.
"It is a really big issue for the agriculture industry," Cole said.
The weevils were imported from the UK four years ago to do what they did best.
"[It's a] pretty cool little dude," Cole said.
"They're pretty small, about 6-8mm fully grown. These guys are really, really well adapted to horsetail.
"Not only will it eat the fern over summer time and eat all of the top stuff off, but during winter time it burrows deep down into their root system and eats as it goes.
"It does a lot of damage to the root as well and that really is the powerhouse for this plant down underneath the ground."
It seemed to good to be true, simply letting Mother Nature do the work, but it's hoped the horsetail would become self-managing in the environment so control methods wouldn't need to include chemicals.
NZ Landcare Trust also hoped working with the students would lift their interest in the field.
"Having Clifton School here in Bulls means that hopefully we can not only help us, but create scientists of the future," Coles said.
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