Invasive Spanish Slugs Devastate Lithuanian Crops and Green Spaces

Widespread Agricultural Destruction

Invasive slug species, primarily identified as the Spanish slug (Arion vulgaris), are rapidly spreading across Lithuania, inflicting substantial damage on agricultural crops, private gardens, and public green spaces. First detected in Kaunas in 2008, these pests have since proliferated throughout nearly the entire country.

Farmers are reporting devastating losses, with entire fields being destroyed shortly after planting, even following the application of chemical treatments. For instance, farmer Giedrius Aleknavičius in Marijampolė witnessed a five-hectare field of winter rapeseed wiped out, despite multiple applications of molluscicides. The slugs feed on leaves, stems, and seedlings, capable of destroying whole plants and rendering crops unmarketable due to faecal and slime contamination.

Contributing Factors and Species Identification

The proliferation of these invasive slugs is attributed to several factors. Unusually wet conditions have created an ideal breeding environment, allowing populations to skyrocket. The Spanish slug, also known as the Lusitanian slug (Arion lusitanicus), is a highly adaptable species. A single adult slug can lay up to 400 eggs, and warm, humid winters coupled with frequent rains during growing seasons further contribute to their successful breeding and survival.

The problem is exacerbated by certain agricultural practices. Minimum- and no-tillage farming, while beneficial in some aspects, can inadvertently create favorable conditions for slugs by not disrupting their populations as traditional plowing would. Additionally, high organic matter content in the soil can support slug population growth.

Challenges in Control and Mitigation Efforts

Controlling the invasive slug population presents significant challenges. Chemical treatments, such as molluscicides, are proving increasingly ineffective, with laboratory studies showing very low mortality rates for Arion vulgaris. Furthermore, the use of broad-spectrum molluscicides can harm native slug and snail species, impacting local biodiversity.

Experts, including Dr. Grita Skujienė of Vilnius University's Institute of Biosciences, recommend continuous control measures from early spring through late autumn, with a focus on destroying eggs and juvenile slugs before populations become unmanageable. Farmers are exploring alternative strategies:

• Deeper soil cultivation: This method exposes slugs to sunlight and oxygen, which can be lethal.
• Manual collection and trapping: Recommended methods include collecting adult slugs and disposing of them by salting in sealed containers.
• Mulching: Studies have shown that mulching with materials like buckwheat husks can reduce damage to plants.

Despite these efforts, the financial burden on farmers is substantial, as there is currently no insurance available in Lithuania to cover damage caused by slugs.

Government Response and Future Outlook

In response to the escalating crisis, the Lithuanian government has pledged financial support. Local municipalities are set to receive €840,000 (approximately $987,042) in the coming year to aid in combating the infestation. However, some local officials, such as Roberta Kelertienė from the Marijampolė municipality, have voiced concerns that this funding is merely 'a drop in the ocean' given the scale of the problem. The Neringa Municipality has also issued warnings against improper disposal of green waste, as it can inadvertently contribute to the spread of these invasive species.