A special weevil has been released in Queensland waterways as a biological control agent to get rid of cabomba, a fast-spreading weed wreaking havoc on our aquatic environment.

We’ve released tiny weed-chomping weevils, smaller than a grain of rice, in Queensland. The weevils have travelled from South America to stop the spread of cabomba, a weed choking our waterways.

Close up of a tiny weevil on a cabomba plant.
The weevil has landed to take on cabomba.

Cabomba weed goes wild

Cabomba (Cabomba caroliniana) is a fast-spreading freshwater weed from South America. It reduces water quality, strangles ecosystems and is harmful to aquatic plants and animals.

The weed was originally introduced to Australia as an aquarium plant sold by aquariums and nurseries. It was either deliberately released into freshwater bodies for commercial purposes, or possibly dumped there. Fortunately, all states and territories have now banned its sale and distribution.

It is highly invasive and exists in waterways from Melbourne to Darwin. Under the right conditions it can grow five centimetres in a day.

How much damage can cabomba weed really do?

Dr Kumaran Nagalingam is the leader of our weed genomics team. He said cabomba weed is affecting our aquatic environments and the native species that live there.

“It forms dense patches and prevents light getting through the water to native species, expelling them from their natural environment,” Kumaran said.

“Mary River Cod and water rat populations are also in decline in some areas where the weed is particularly fierce. Platypus numbers are also lower in cabomba-infested creeks relative to un-infested creeks in northern Queensland.

“It affects water quality, reduces the water holding capacity of dams and makes the cost of treating drinking water more expensive. In a country like Australia where water is a precious resource, cabomba is bad news.

“And it’s not just a problem for our aquatic wildlife; cabomba causes problems for humans too. It creates a health and safety issue for people working in and around waterways infested with this weed. And it negatively impacts recreational activities such as swimming, fishing, paddling and boating,” Kumaran said.

A scientist wearing a CSIRO hat and personal protective equipment is carrying a long metal pole with cabomba weed on the end of it out of a lake.
Dr Kumaran Nagalingam collecting aquatic plants for pre-release biomass monitoring.

Weevil imports, quarantine and testing

We’re working with one of our country’s largest water asset managers, Seqwater. We’ve imported an army of cabomba weevils (Hydrotimetes natans) from South America to help rid our waterways of cabomba weed. The weevils feed and develop exclusively on cabomba. They spend their entire life on the weed, making these tiny insects the ideal biological control tool.

The weevils have quarantined in our labs. To confirm they won’t damage our native plants, we’ve exposed the weevils to 17 native species over a 150-day period. This is enough time to produce three generations of weevils. Significantly, the weevils showed no interest in our native plants and continued to only eat the cabomba weed.

These tests were part of extensive research undertaken in South America and Australia which showed the weevils are not a risk to other species.

Hope for our waterways

Drone image of a lake (Lake Kurwongbah) surrounded by trees.
The site of the first mass weevil release, Lake Kurwongbah, a dam north of Brisbane.

Lake Kurwongbah, a dam north of Brisbane, was the site for the first mass weevil release in December 2022. Lake MacDonald (also north of Brisbane) will be next. We’re working with partners to introduce the weevil to other infested waterways in central Queensland, northern New South Wales and then other states and territories.

The introduction of weevils and banning the sale of cabomba will stop its spread and free our waterways of this aquatic weed.


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