Australian invaders in Cornish gardens

Australian flatworm Australoplana sanguineum_Rowena Millar

One of the great pleasures of having a garden is being able to look underneath pots, logs, and stones to see what living things are hiding underneath. Perhaps the most surprising things I’ve found are Australian flatworms. Maybe you have them in your garden too.

My own flatworm story began 25 years ago. One evening I spotted shiny pink, ribbon-like creatures by torchlight, sliding around outside our back door. You can read the original story on my blog.

My discovery of the strange stretchy creature, now described as Australoplana sanguinea, coincided with other reports of Australian and New Zealand flatworm finds, and led me to send live specimens to a PhD student in Belfast. These multiple-eyed planarians were thought to have entered the UK in the pots of imported plants (the first record was in 1980 on the Isles of Scilly). We had moved to our house in late 1993, so the flatworms almost certainly arrived before we did.

Since 1995 I have become used to finding Australoplana sanguinea every now and again. They dissolve earthworms in a disgusting way, and earthworms are hugely important for our soil. They break down organic matter, releasing nutrients that can be used by plants through the actions of bacteria and fungi on the digested particles they excrete. They also mix soil layers and create countless little spaces as they burrow, so that soil becomes looser, softer and crumblier – accessible to air, water and roots. Thankfully, our earthworm population has recovered well.

an inconspicuous orange worm-like creature lies amongst soil. The worm is very ting and orange

Australian flatworm Australoplana sanguineum_Rowena Millar

A new flatworm?

In mid-April this year, there were pink Australian flatworms lurking in my greenhouse, but I had a surprise towards the end of the month. Under a small pot, standing on soil inside a large one, was a jet black flatworm, waving its narrow front end in the air in that distinctive flatworm way. I had heard of the dreaded New Zealand flatworm, but this was smaller. Could it be a two-eyed British species? I didn’t think so. It was long, lithe and robust, rapidly exploring new indoor surroundings. It didn’t seem to contract to a blob when disturbed, so not a freak colour variation of Australoplana sanguinea.

I contacted Cornwall Wildlife Trust’s Wildlife Information Service, who passed the record on. Our top British planarian specialist is Dr Hugh Jones. His accessible paper introducing and describing land flatworms can be found here.

I received an email from Dr Jones and was excited to hear that my description didn’t seem to fit other records, so I wondered if I had made a startling new discovery. Unfortunately, the flatworm was no longer alive.

On 27th April, however, I found another shiny black flatworm in the garden, and contacted Dr Jones immediately. He was keen for me to photograph its underside, which can help a lot with identification. Invasive flatworms come in various colours but also with different numbers and patterns of stripes.

the middle of the picture is a jet black flat worm about 2inches long and thicker at one end than the other

Dorsal side of Kontikia ventrolineata_Rowena Millar

I was hoping to send it alive, but this could have been risky, as some flatworms – like a little creamy white one I found under a rock down the lane on 1st July and tried carrying home on my fingertip – can spontaneously disintegrate. These black ones were more robust, but the advice was to send them in alcohol, and we happened to have a bottle of isopropyl alcohol cleaning fluid.

First, I read a lot of information about preserving invertebrates, then phoned Sue at the post office to check the time of the last post. She was concerned about the legalities of sending a very strong alcohol solution by post, so we then both looked up the correct protocol. Fortunately, I was allowed to send a small amount in a small plastic pot, stuffing cotton wool into the top of the bottle to fill up the rest of the space. Then after the fatal drop, in which my long, healthy worm went into a sort of rigor mortis on contact with the solution, instantly contracting and turning grey (which gave me a pang of both guilt and disappointment), there was the hurried sealing, taping, padding, wrapping and addressing, then a dash to the post office.

The flatworm arrived successfully the next day, and was identified as Kontikia ventrolineata.

Apparently it has two paler lines on top, either side of a midline, although I couldn’t make them out. Another of the same species had been found a few miles away in woodland near Tavistock, Devon. Unlike Australian ‘pinkie’, this species seems to be a scavenger, so much less of a threat to the earthworm population.

what appears to be black bird poo on the end of a finger

Kontikia ventrolineata on my finger, with stripes showing_Rowena Millar

My feeling of guilt was somewhat assuaged when I found another one that same evening, under a block of granite by the door of our duck house.

Dr Jones is interested to find out what it will eat, as they have been seen consuming ‘all sorts of things, including strawberries!’ The RHS source describes its prey as ‘small snails and possibly slugs’. So the newest black flatworm is living in a tub of mixed compost and I am giving it various food samples on a little plastic tray. So far I haven’t noticed it eating anything and I think it’s getting smaller.

camoflauged amongst dirt and decaying leaves lies a small jet black flatworm

Kontikia ventrolineata now in a plastic container, July 2020_Rowena Millar

Other non-native flatworms in Cornwall

A species called Artioposthia exulans was found in 2013 in the Newlyn and Penzance areas in gardens and fly-tipped garden refuse, and is thought to be a recent introduction from New Zealand. It is light brown with darker brown marbling and a thick brown stripe down the middle.

Around 14 others are mapped as having been recorded in Cornwall, with my two definitely the most common, and only one or two records of many of the others. There seems to be a cluster of some species in the far west.

An orange flatworm and a black flatworm intertwine

'Pinkie' Australoplana sanguineum meets 'Blackie' Kontikia ventrolineata _Rowena Millar

What you can do about invasive flatworms

If you would like to find out if you have Antipodean flatworms in your garden, pick a damp evening or morning (any time of year) and start looking under various objects including paving slabs and compost bags. Send in your records to ORKS take part in Buglife’s flatworm survey and/or contact Dr Jones [mail to] at flatworm@btopenworld.com

To optimise your garden for native earthworms and deal with flatworm invaders:

• If you see non-native flatworms or their eggs, which resemble seeds or berries ( Dr Jones has an article with more information here), collect them (some people are sensitive to flatworm mucus, so wear gloves if concerned) and send them for ID or if you know what they are, drop them into salt water or vinegar to kill them. For the squeamish, I have found that putting them in a dry and very well-sealed box or jar causes them to disintegrate quite soon (but watch out: they can escape through screw caps). Chopping them in half is a bad idea; they may regenerate and multiply if broken!

• Grow plants from seeds or cuttings and avoid exotic imports or other people’s soil that may contain non-native flatworms or their eggs.

• Don’t overdo the tilling, to protect earthworm habitat. A no-dig approach (except for making planting holes) keeps life in your soil undisturbed and happy. The earthworms will do the tilling for you.

• Leave some organic matter, like leaves and grass clippings, on the surface of the ground, for worms to drag underground.

• Put manure and compost on your garden, but no chemicals, please.

• Keep your earthworms cool and hydrated with mulch.

• Australian flatworms arrived without their native predators, but some ground beetles might attack them. Make predatory beetle homes: raised beds with native grasses and mulch, rocks and logs are excellent beetle habitat.

Here to stay?

Although a Cornish wildlife garden may be a superb habitat for invasive flatworms, it will be resilient, with the means to rebuild wildlife populations after a predatory flatworm attack. Native species have been here for millennia, and so whether the flatworms assimilate and become part of our fauna or die out in a hard winter, they might be less likely to survive all British conditions than our native species … unless we change our soil, our landscape and our climate until Cornwall resembles.