Yellow-striped Flatworm

Fast Facts

Latin name: Caenoplana variegata

Notable feature: Invasive Non-Native Species (INNS) in the UK

Conservation Status: Not Evaluated

Where in the UK: This Invasive Non-Native Species (INNS) is mainly reported in southern England and Wales

Yellow-striped Flatworm (Caenoplana variegata) © G.Pearce


The Yellow-striped Flatworm (Caenoplana variegata) is a non-native species, originating from Australia; it is considered invasive as it is spreading rapidly and its presence is impacting our native wildlife here in the UK.

The Yellow-striped Flatworm is a long thin flatworm, ordinarily dark brown in colour, with a distinctive bright yellow stripe which runs from head to tail; the yellow stripe also has two narrow brown lines within it.  This flatworm can measure up to 15cm in length (sometimes longer) and is between 2-5mm wide.

It has several small black eyes at it’s “head end” and along its side – these are difficult to see without magnification

The Yellow-striped Flatworm was recorded in the UK in 2008, since this time it has been found in several locations across the UK.

    • Size: 5-15cm in length (but can be longer)
    • Life span: Undetermined (given their ability to reproduce by fission, a flatworm potentially never dies)
    • Diet: The Yellow-striped Flatworm feeds on arthropods such as woodlice, insects and spiders.
    • Reproduction: Reproduces mostly by fission; small pieces 1-2cm long break off and each regenerate into a larger worm.
    • When to see:  Generally more visible/noticeable during spring/autumn; possibly because this is when people tend to do more in their gardens
    • Population Trend:  Increasing numbers of reports across England and Wales, mainly in the south
    • Threats: There are no recorded natural enemies and no biological or pesticide control methods for non-native flatworms, the key control measure is to prevent their introduction to new areas.
    • Fun Fact:  There are variations in the pigmentation of Yellow-striped Flatworms. This has led to different names given to the specimens found in the UK, including the Southampton Flatworm (Caenoplana bicolor). Studies have since found no distinction between species and they are now recognised as Yellow-striped Flatworm.

As with other flatworm species the Yellow-striped Flatworm is likely to be distributed via the movement of plants and growing media in the horticultural trade.

How you can help: 

Buglife is working to increase awareness of Invasive Non-Native Species (INNS) and their, often detrimental, impacts on our native wildlife and habits.  Working with other organisations to highlight how biosecurity is everyone’s responsibility and that we can all play our part.

Join a recording scheme and log your flatworm finds – send any records/sightings to our flatworm recording scheme – Potwatch!

Follow our biosecurity guidance (at the bottom of the linked page) on flatworms to help prevent their spread and destroy any non-native flatworms that you find.

Do remember that we rely on donations to continue our work.  If you have searched, found and learnt about our incredible invertebrates on our website, please do consider Making a Donation, Becoming a Member or maybe even making a purchase in our shop.  For more ideas on how to support our work find out how to Get Involved.  Thank you 🕷