Slug
Gastropoda
7 host plants
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
The Puget Sound lowlands are slug country, not snail country. The brown garden snail (Cornu aspersum) is present but secondary; damage is overwhelmingly from slugs. The maritime climate gives slugs a roughly 9-month active season (September through June), suppressed only during dry weeks of July and August. The PNW Insect Management Handbook calls slug control 'often a year-round necessity' in western Washington and Oregon. Heavy silt loam soils (Woodinville Series) retain surface moisture and provide ideal egg-laying substrate. All major pest slug species are European introductions thriving in a climate that mirrors their native maritime range. National advice to 'water in the morning, not evening' is irrelevant during October through May rainfall. Cultural controls that matter here are habitat modification and drainage, not sprinkler schedules. (PNW Insect Management Handbook; spring-slug-snail-management guide)
— Chris Welch, ISA Certified Arborist
Slugs create holes and ragged edges on rose, strawberry, and other plant foliage and stems in gardens; characteristic slime trails mark their movement and feeding sites. Slugs chew holes with smooth edges between leaf veins, and seedlings may be completely consumed leaving only midribs and stumps. Sausage-shaped feces in the garden indicate slug presence.
Reduce habitat by pruning lower branches to allow sunlight and air circulation. Place boards under plants and hand-collect slugs each morning. Beer traps attract slugs to drown. Copper barriers deter slugs by reacting with mucous. Iron phosphate bait is safe around children and pets.
Quick Reference
Monitoring & Action
Board traps (12x15 in, elevated 1 in off soil on small sticks) placed near vulnerable beds in late afternoon, checked each morning; scrape slugs into soapy water. Beer/yeast traps (container buried to ground level, 1 in beer or 1 tsp yeast in 1 in water; replenish every few days). Bread dough attractant (500g flour, 500mL water, 0.5 oz yeast) as a lower-cost alternative (PNW Insect Management Handbook). Hand-check on damp evenings 1-2 hours after dark with flashlight. (Cornell IPM; UC Davis IPM Pest Note 7427; PNW Insect Management Handbook)
No quantitative density threshold established in the literature. Extension sources provide qualitative guidance: intervene when damage is first noticed on vulnerable plants, or when board traps consistently yield slugs each morning. Fall baiting triggered by first sustained autumn rain (September-October) regardless of observed damage, because it targets egg-laying adults before the spring generation is produced. (OSU Extension; PNW Insect Management Handbook) [VERIFY: no published numeric threshold found across UC Davis, Cornell, OSU, or PNW Handbooks]
Irregular holes with smooth edges in foliage (the radula scrapes rather than tears). Feeding damage concentrated between leaf veins and along leaf edges. Slime trails visible on soil and plant surfaces, drying to silvery sheen in morning light. Pretzel-shaped fecal droppings at the base of damaged plants are a diagnostic confirmation when trails have dried or been rained away (WSU HortSense). Damage heaviest along field margins and near weedy or grassy borders that serve as daytime habitat (PNW Insect Management Handbook). Strawberry damage distinctive: holes chewed under the cap where fruit contacts soil (spring-slug-snail-management guide). Seedlings and transplants disproportionately vulnerable compared to established plants.
Cultural Controls
- Remove daytime hiding spots
- Transplant sturdy starts rather than direct-seeding in slug-prone beds
- Encourage and conserve natural predators
- Deploy board traps for monitoring and population reduction
- Hand-pick on damp evenings
- Set beer/yeast traps