Blue garden flatworm

The blue garden flatworm (Caenoplana coerulea) is an invasive species of predatory flatworm native to Australia, now established in various parts of the world. It belongs to the order Tricladida and the family Geoplanidae. Due to its diet and ability to adapt to artificial environments, it is considered a significant threat to soil ecology in many gardening regions.

Physically, the adult worm is elongated, reaching lengths of up to 10 centimeters, with a characteristic dark blue or metallic coloration and a distinct longitudinal stripe. They secrete a sticky mucus that allows them to glide across surfaces and entrap their prey efficiently. They lack a shell or protective covering, relying entirely on moist environments to survive.

This species is classified as a pest because it is a specialist predator of earthworms. By preying on native and introduced earthworm populations, Caenoplana coerulea disrupts the essential processes of soil aeration, organic matter decomposition, and nutrient cycling. This leads to reduced soil productivity, which ultimately harms the health and vigor of ornamental plants and crops.

Their life cycle revolves around the production of egg cocoons, which are deposited in damp, dark crevices, such as under logs, stones, or pots. Once hatched, the young flatworms quickly begin hunting. Because they are hermaphroditic and can reproduce both sexually and through fragmentation, they can establish stable colonies in greenhouses or moist garden beds very rapidly.

Management strategies focus primarily on preventing the spread of the pest through plant transport. Key control actions include:

• Quarantining all newly purchased plants before integrating them into the existing landscape.
• Regularly clearing organic debris and weeds that provide hiding spots.
• Hand-picking and destroying individuals during damp evenings.
• Reducing excessive moisture in greenhouse conditions to make the environment less suitable for survival.