The Spanish slug is widespread across Estonia. Krynickillus melanocephalus has appeared in gardens over the past few years. The Spanish slug and Krynickillus melanocephalus mostly feed on garden produce and agricultural crops.
They usually get into gardens via potting soil or the soil around a plant’s roots that may conceal both adult specimens and eggs. All it takes for the species to start multiplying in the garden is two specimens or an egg cluster. The population growth is supported by a humid and warm spring and summer and mild winters.
It is recommended to take preventive measures to stop the slugs from settling into your garden. Once the uninvited quests have arrived, they should be eradicated consistently and in cooperation with the rest of the community.
Please make sure that it’s an alien species – check the identifying characteristics and include a photo.
Anyone can mark a sighting spot on the map, whether that’s in their garden, their neighbour’s garden, at the side of a road or by a lake.
We appreciate all information on sightings across Estonia. Please make sure that it is the Spanish slug or Krynickillus melanocephalus. Check the identifying characteristics and include a photo.
The Spanish slug
The Spanish slug (Arion vulgaris, cлизень испанский) is originally from Portugal and has spread across Europe with the help of human activity. It was first registered in Estonia in 2008. Changes to arable farming methods, bans on after-crop and straw burning, a drop in the number of natural limiting species and the soaring increase in international plant and vegetable trade have all contributed to the spread of the slug.
The eggs of the Spanish slug closely resemble fertilizer pellets, which makes it difficult to easily identify them in the root balls of plant seedlings. However, the eggs are a bit more translucent and usually clustered.
The herbivorous Spanish slug is attracted to juicy vegetables (e.g. cucumbers, gourds, lettuce), decorative plants, crops and mushrooms. It also won’t say no to degrading plant parts, fermenting vegetables and, should the population density be very high, even its own dead companions.
Common habitats are poorly maintained and seldom mowed gardens with thick vegetation, grasslands, parks and humid deciduous forests, as well as greenhouses. They are mostly active at dusk and night, but you might also see them during a rainy day. If the winter is warm and there are good conditions for them to take cover, the Spanish slug has no problem with successful overwintering.
Characteristics
- The Spanish slug is remarkably large in size – the body length of an adult animal is 7–15 cm.
- It has no shell.
- The colour of the body may vary from dark brown to reddish, orange, yellow and beige tones. Young animals often have a slightly darker longitudinal stripe on both sides of their body. The mucus covering its body is orange-yellow.
- The foot fringe is characteristically bright in colour, with clearly visible darker grooves (stripes). The head is usually darker than the rest of the body.
- The respiratory hole is at the front of the mantle shield.
- Whitish eggs of about 3 mm in diameter are laid in batches of 20–30 (40) under the litter layer of soil, in a compost heap or other sheltered humid places. The eggs hatch after 3.5–5 weeks and the hatchlings reach sexual maturity (capability to lay eggs) as early as six weeks. One specimen may lay up to 400 eggs.
There are five more species of the Arion genus registered in Estonia: the brown-banded arion, orange-banded arion, garden slug, forest arion and dusky arion. All these species are significantly smaller in size. Similar in size are the domestic slugs of the Limax genus: the black keel-back slug and leopard slug.
Domestic slugs
The Dusky Arion (Arion subfuscus) is a domestic species that is the most similar in appearance to the Spanish slug.
- Medium-sized species; the body length of an adult Dusky Arion when extended is 5-7 cm.
- Its' color varies from grayish yellow to even reddish brown or black. The head and senses are usually reddish brown.
- Two dark bands on the sides, located relatively high. The bands may be diffuse in color or almost imperceptible.
- Sole light gray to white, not dark. The edge of the sole is the same shade as the sole, usually with thin dark cross lines.
- Body mucus, especially on the mantle shield is characteristically yellow or orange. The body's mucus smears the contact surfaces yellow, although it is less dense than in Spanish tea. The mucus of the sole is colorless.
- In a resting or protective pose, it becomes an elongated low dome or segment in side view, not a hemisphere like a Spanish road.
Photo: Piret Eensoo
One of the domestic species most similar in size is the black keel-back slug (Limax cinereoniger, чёрно-синий слизень).
- The body length of an adult black keel-back slug is 15–20 cm.
- The colour varies from gray to brown and black with lighter stripes, the mantle shield is black.
- The respiratory hole is at the rear of the mantle shield and the mucus is colourless.
Another domestic species similar in size is the leopard slug (Limax maximus; большой слизень).
- The body length of an adult leopard slug is 10–20 cm.
- The colour varies from light gray to grayish brown with darker stripes and spots, the mantle shield is also spotted.
- The respiratory hole is at the rear of the mantle shield and the mucus is colourless.
Krynickillus melanocephalus
The natural habitat of Krynickillus melanocephalus (черноголовый слизень) is the Caucasus, Crimea, Northeast Turkey and Northern Iran. The species was first registered in Estonia in 2013.
Krynickillus melanocephalus is mainly spread by human activity: via ornamental plant trade, soil transport, flower pots, used plant substrate and garden waste.
Krynickillus melanocephalus are herbivorous and prefer juicy vegetables (pumpkin, zucchini, lettuce, cabbage). Signs of feeding have also been observed on hostas, horseraddish, rhubarb, apples on the ground and raspberries.
In the wild, Krynickillus melanocephalus prefers humid locations under rocks, deadwood and ground vegetation in fresh boreo-nemoral forests and flooded meadows. In urbanised areas, their preferred habitats are gardens (compost piles) and the surrounding barren lands, parks and cemeteries.
Characteristics
- Grown specimens of Krynickillus melanocephalus are small to medium-sized slugs with a body length of (3.5) 4.5–5.5 (6.2) cm.
- It has no shell.
- The body is light, whitish gray, the edge of the respiratory hole is paler than the base colour.
- A characteristic trait is the deep or bluish black colouring of the head and tentacles.
- For most specimens, the rear edge of the mantle shield is light, from grayish yellow to grayish white, and contrasts the darker forepart and the abdomen.
- The mucus is colourless and watery.
Prevention and eradication
How to prevent the Spanish slug and Krynickillus melanocephalus invading your garden?
- don’t bring flowers and bushes from areas inhabited by alien slug species into your garden;
- if you purchase seedlings and suspect that they might contain Spanish slug eggs, quarantine the seedlings for five weeks: put a plastic bag around the root ball, securing it tightly around the stem, and check occasionally to see whether slugs have hatched inside the plastic bag. Keep the seedling in a suitable location (lighting, temperature) and water it;
- you may also inspect the root balls of purchased seedlings and destroy any (potential) eggs found;
- if the area is known to be infested with Spanish slugs, so called slug barriers may help - these are smooth tin barriers that are difficult for slugs to climb. However, the Spanish slug is a relatively good climber.
How to act if there are Spanish slugs or Krynickillus melanocephalae in your garden?
- persistently pick up all adult slugs because each specimen can lay a large amount of eggs;
- kill the slugs by halving them with a shovel blow or putting them in a container and pouring boiling water onto them. Dead specimens can be buried in a shovel-deep hole where conditions are not suitable for the development of eggs and that is too deep for the slugs to climb out. Those near Tallinn may bring dead specimens to the Tallinn Small Animal Crematorium (Raba 40) where they will be cremated for free;
- watermelon rinds and beer cans can be used to lure the slugs into one location so they can be easier to pick up;
- make sure to tell your neighbours to also pick up the slugs from their garden, otherwise getting rid of them will be impossible;
- live slugs should definitely not be taken elsewhere (forest edge, meadow, park) as this will just help them spread further and they may later return to your garden;
- garden waste (e.g. raked leaves, cut plant stems and leaves, old mulch) must not be taken to a forest, meadow, park, into thickets or barren lands, as it may contain slugs or their eggs. In such locations they can live and reproduce undisturbedly, as there is no one there to pick them up. Sooner or later they will find their way back to someone’s garden. Garden waste should be composted in your own garden or garden waste treatment solutions prescribed by the local government should be used;
- maintain your garden - keep the grass cut low, the soil loose. Constantly check possible hiding spots for slugs and eggs (areas under big flower clumps and bushes, terraces, undersides of any edges) and maintain them (dig the soil, mow). Don’t forget to destroy the eggs (pour boiling water over them);
- slug poisons are not very efficient against alien slug species and only kill useful domestic species instead. You’ll also poison any birds and animals (e.g. hedgehogs) feeding on them and the poison may even reach domestic animals (cats and dogs).
Make sure that you are eradicating an alien species. Learn the identifying characteristics and protect our domestic species.
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Last updated: 12.04.2024
