Very little is known about the strange flatworms that crawl in the Netherlands. But since 2012, interest in this matter has increased. Nine new, non-native species of ground flatworms have been identified in the Netherlands. Not only that: exotic species are already known to exist in more and more locations, and a number of species have now settled in the Netherlands. There is an urgent need to monitor these animals: from a Hazard Analysis from the University of Nijmegen It shows that the New Zealand earthworm (Arthurdendyus triangulatus) is detrimental to soil fertility. It is very good at overcoming earthworms, which must maintain aeration of the soil.
This species has been on the European Union’s list of invasive alien species for some time, and is already widespread in England. So far it has not been found in Holland, but it is possible that it can be found here as well. So NVWA invites you to be alert to the emergence of this monster. While searching, you may come across a relative: in October, a strange number ten was found in a designated park in Aagtdorp: the multi-streaked hammerhead flatworm (Diversipalium multilineatum). Beautiful dark yellow monster with brown background stripes and amazing triangle head. The length of the animal can reach more than twenty centimeters.
“This is a special find, hammerheads are rare in the Netherlands,” says Setsek de Wart, who works at Naturalis as group manager for Tricladen (flatworms) and coordinator of the EIS working group on earth flatworms. Exotic ground flatworms usually enter Europe from Australia, New Zealand, Southeast Asia and South America. The hammerhead flatworm was first discovered in Europe in 1878, in a greenhouse at the Botanical Gardens in Kew, England. This is reflected in the name of the beast: Quince peplum. It is not surprising that England was the first country where exotic species appeared: the English have a rich tradition of gardening and imported all kinds of beautiful plants from the colonies for their gardens and greenhouses. And flatworms happily scattered.”
“The first recording of this species in the Netherlands was in 1912, in the Amsterdam Hortus. Since that time, the monster has been found sporadically in Dutch greenhouses. It is therefore characteristic that the multi-streaked hammerhead now appears in the Aagtdorp. How it got there is unknown. …it may also have been associated with a trip with the international pot plant trade, because that’s why it’s so popular. So you can bring the animal into your home with plants from the garden center.” The discovery unintentionally illustrates a special property of earthworms, their ability to regenerate. De Waart: “Roy Kleukers from the EIS Knowledge Center has beautiful pictures and a Movie Made by Discover Lonneke Klein-Aarts. Here you also see a kind of stem, without a hammer head. And this is a great illustration of how this regeneration works: flatworms can separate part of them, for example the tip of the tail, and then a whole animal grows in a few weeks, including the characteristic head. “
The dangers of exotic species
They are beautiful and very distinctive creatures, but as with all exotic species (think Japanese knotweed or Asian hornets), they can also cause problems in their new home. from one species of the earthworm, the New Zealand flatworm (Arthurdendyus triangulatus), is known to be harmful. This is why it was already placed on the European Union’s List of Exotic Species of Concern in 2019. This earthworm feeds on earthworms. This can cause earthworms to disappear locally, negatively affecting biodiversity and agricultural crops.
And what about the other nine alien species from the past ten years? And for example, find out the new hammerhead, is it harmful? De Wart: “Naomi Thonesen, a PhD candidate last year from the University of Nijmegen, received her Risk analysis Made from flatworms that are found in Holland, or that can live in our climate. Too little is known about most of these species for you to make a proper analysis. To determine the damage, you need to know, for example, whether a species can survive outside the greenhouse in the Dutch climate, and what that species eats. And how evil it is. But for the time being, we suppose that only the New Zealand earthworm is harmful, and that it should be prevented from settling here in Holland, as it has already done in England.”
Contribute to our knowledge
Earth flatworms discoveries reports help to get an idea of the distribution (worldwide) and potential harm of earth flatworms. You can look for these creatures in places that are cool, humid, and relatively dark. During the day they hide under shelves, pots or pieces of plastic. At dusk, they go out to search for small prey, such as earthworms and snails.
How do you get to know them? Despite their name, flatworms on Earth are usually not very flat, but rather “plump”. External features can help determine: head shape, colour, dorsal stripes, and eye pattern. The two original species (the flatworm dark and flat with two stripes) are small (1 to 3.5 cm) and not very visible, with their gray, brown or black bodies. Non-native ground flatworms as adults are often more than ten centimeters long, usually have more abundant colouring, striking dorsal stripes and sometimes an amazing spoon-shaped head (hammer head).
Wild worms can be collected as follows: place the worm with the help of a leaf, twig or brush in an airtight container with some leaves and wet leaves. They can go without food for a long time, but they are poorly resistant to drought, heat and light. So keep it in a cool, dark place (but not in the fridge, it’s too cold). For naming, use search card or the digital species finder. Try to take good photos of live animals and report them to Waarneming.nl or [email protected]. “Because so much is still unknown about ground flatworms, it is very important to continue to monitor them closely,” says de Wart.
Hammerhead flatworm samples will be added to the ARISE database. arise It is a massive project that aims to build an infrastructure that will identify and monitor all multicellular species in the Netherlands. ARISE will build a DNA database of low-exposure groups from the Netherlands that are in the Naturalis collection, such as ground flatworms.
Text: Sytske de Waart, Earth Working Group Flatworms EIS Insect Knowledge Center in a Natural Biodiversity Center
Images: Roy Klickers, Insects Knowledge Center EIS
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