GARDENERS face no greater crisis than New Zealand flatworms. They clear a garden of earthworms, leading to sour, airless, com pacted soil. Although flatworms prey on any earthworm, studies by Dr Brian Boag of the James Hutton Institute have shown that Lumbricus terrestris is the most vulnerable species. This worm feeds on the soil surface and creates the vertical tunnels that are vital for drainage.

These alien invaders first arrived in Northern Ireland in the 1960s, appeared in 1965 in the Edinburgh Botanics and have now spread throughout the UK.

Flatworms are between 5 and 15cm long, flat with a dark purply brown topside and a creamy pale underside and edge. They’re pointed at both ends and, like slugs and snails, leave a sticky mucus trail behind them. In summer, they lay an egg every 7-10 days, with each usually containing 6 or 7 young. Look out for these shiny, blackcurrant-like cocoons.

I know people are surprised that their earthworm population never seems to recover, imagining the flatworms would die out once they’d disposed of their prey. The answer is horribly simple. The predators degrow, shrinking to as little as 10% of their original body weight, until a new source of food lets them regrow again.

Flatworms are present throughout Scotland, with sightings in Glasgow, Ayr, Inverness, Dingwall and Castle Douglas to name a few. So, wherever you live, vigilance is essential to keep them out of your own garden.

Flatworms can travel between gardens, so if a neighbour’s garden is infested, you must be especially watchful, setting traps close to a boundary fence. They shelter in cool, damp places, so place slabs of wood or stone there, lift them regularly and put flatworms in warm, very salty water to kill them.

You should also check pots of new plants. Nursery and garden centre stock should be perfectly safe, but take care with any from friends or a plant exchange. And, if you do have flatworms, never give any plants to friends. Place a pot in a bucket of warm water,?30C, for 40 minutes to kill adults.

This treatment won’t affect eggs, so the alternative is to remove the plant from its pot. Over a large bowl or bucket, wash away the soil to flush out any adults or eggs. Dispose of the soil safely and not into the garden or compost heap.

If you have a resident flatworms, keep trapping, as I describe above. You will gradually reduce their numbers and there may be a small recovery in earthworm population, but don’t hold your breath. Trials have been conducted which show that potential predators, rove beetles, Staphylinidae, and ground beetles, Carabidae, are reluctant consumers. I’m afraid your only long term solution may be a visit to an estate agent.

On a more positive note, you can help researchers better understand flatworms, in the hope that some solution may be found.

Dr Annie Robinson of Aberdeen University and Dr Brian Boag from the James Hutton Institute, Dundee are running a research programme to find out how far and widely flatworms have spread and the effects on local environments.

The project is part of a UK-wide citizen science initiative, OPAL, Open Air Laboratories. In this case, they’d like gardeners to report and photograph flatworm sightings, and would also be interested to hear of unaffected places.

Dr Robinson says: “Carrying out the survey is really straightforward. Search your garden, allotment, school grounds or public spaces for 10 minutes, focussing on dark damp places like under pieces of wood, stones or plastic. If you think you have found a New Zealand Flatworm, please take a photo and submit it along with its location via the OPAL website: www.opalexplorenature.org/nzflatworm

Since the project started in 2015, 1500 people have taken part and the scientists would especially welcome information from Orkney, Shetland, Skye, the Western Isles, Caithness, Fort William, Dumfries and Galloway and the Borders.

Jobs in the fruit garden

Check stakes, supports and tree ties for wind rock or constriction. Replace or renew as necessary. Cut out dead, dying or infected branches from apple and pear trees, but not stone fruits like plums and cherries. Clear away weeds and grass from around young trees to reduce competition.

Pick off any remaining fruit from trees as they can harbour disease. Entice birds into the fruit garden with feeders and fatcakes. They help control overwintering aphids and cocoons.

If a fan-trained peach has been infected with leaf curl, build a simple rain-proof structure to keep rain off newly forming buds in early spring.

Plant of the Week

Calendula officinalis ‘Indian Prince” is still flowering bravely. Cheerful, deep orange petals with tawny backs glow brightly whatever the weather.