# Slugs and snails: night shift on your seedlings

> Slugs and snails, above all the gray field slug Deroceras reticulatum, chew smooth-edged holes in cannabis seedlings and young transplants at night in cool, wet weather. They lay clutches of about 10-40 eggs and do best near 17-20 C. Scout at night or under boards, protect seedlings with iron phosphate baits, copper barriers and traps, and remove hiding places.

- Canonical: https://genetixbay.com/knowledge/pests/slugs-and-snails.html
- Category: Pests · Level: Beginner
- Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Seedling, Veg · Systems: Soil, Living soil
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**What is eating holes in my cannabis [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) at night?** If cannabis seedlings or young [transplants](https://genetixbay.com/knowledge/glossary/transplanting.md) have irregular holes with smooth edges, or are clipped off overnight, and you see silvery slime trails in the morning, slugs or snails are the likely cause. The gray field slug Deroceras reticulatum is the most common culprit outdoors and in greenhouses. Confirm by checking with a flashlight two to three hours after dark, especially after watering or rain.

**When are slugs most active?** Slugs are most active at night and on cloudy, foggy or rainy days, when the ground and leaves are wet. They hide from sun, heat and dry air under boards, mulch, pots and debris. In cold weather they shelter in the topsoil, and hot, dry periods stop activity. The gray field slug Deroceras reticulatum develops and lays eggs best at about 17-20 C.

**How many eggs do slugs lay?** A gray field slug (Deroceras reticulatum) lays clutches of about 10-40 eggs, typically around 20, in soil cracks and under debris. In a Korean lab study a slug laid about 217 eggs in total at 20 C but only 105 at 16 C, and field estimates reach about 500 eggs a year. Eggs hatch in roughly 2-4 weeks depending on temperature.

**Are iron [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) slug baits safe around pets?** Iron phosphate slug baits are considered safer around children, pets and wildlife than metaldehyde baits, which are highly poisonous to dogs and cats. Slugs stop feeding soon after eating iron phosphate but take several days to a week to die, often out of sight, so you rarely see bodies. Some iron phosphate products are allowed in organic growing; follow the label and local law.

**Do beer traps work for slugs?** Beer traps catch slugs, but only those within a few feet of the trap, so they are a monitoring and small-garden tool rather than a field solution. Use a deep-sided container sunk with its rim at soil level, covered with a lid that has entry holes, and refill it every few days. A sugar-water and yeast mixture works in place of beer.

**Do [copper](https://genetixbay.com/knowledge/glossary/copper.md) barriers stop slugs?** Copper barriers deter slugs and snails when they are tall enough and kept clean. UC IPM recommends a copper strip at least 5 cm (2 in) tall, buried 2.5-5 cm (1-2 in) into the soil so slugs cannot go under it. Copper bands on pots and planters work until they tarnish; clean them with vinegar. Barriers fail if a slug is already inside.

**Why are seedlings most at risk from slugs?** Seedlings are most at risk from slugs because a cannabis seedling has only a few small, succulent leaves and a soft stem, so one night of feeding can remove all its growing points or cut it off at the base. Older plants lose some leaf area but survive. Protect seedlings and transplants until stems firm up, usually the first 2-4 weeks outdoors.

**How long do slugs live and how many generations do they have?** The gray field slug Deroceras reticulatum lives about a year and has one to two generations a year. A Korean lab study found egg-to-death lifespans of 151-216 days at 16-28 C, with juveniles taking 51-68 days to mature. UC IPM gives 3-6 months from hatching to maturity, depending on species. Mixed-age populations peak in spring and autumn.

**Short answer.** Smooth-edged holes and clipped seedlings overnight, with silvery slime in the morning, mean slugs or snails, most often the gray field slug *Deroceras reticulatum* [1]. They feed at night in cool, wet weather and hide by day. Seedlings and fresh transplants are the ones that die. Scout with a flashlight or boards, protect young plants with iron phosphate baits and copper barriers, trap, and remove hiding places [1].

## Which slugs and snails attack cannabis?

The slugs that attack cannabis outdoors and in greenhouses are the same garden slugs that attack vegetables: the gray field slug *Deroceras reticulatum*, banded and three-band garden slugs (*Lehmannia* spp.), the tawny slug *Limacus flavus* and the greenhouse slug *Milax gagates* [1]. The brown garden snail is the common snail [1].

No published study of slug damage to cannabis specifically was found; the biology below is from vegetable and lab studies and is extrapolated (*Supported*).

## How do I recognise slug and snail damage?

Slug and snail damage on cannabis is irregular holes with smooth edges, chewed leaf margins, and seedlings cut off at the base overnight [1]. Silvery mucus trails on leaves, pots and soil confirm slugs or snails, because earwigs and caterpillars make similar holes [1]. See [kb-pests-caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md).

Seedlings are most at risk because slugs prefer succulent tissue and a seedling has little to lose [1]. Older plants lose leaf area but survive (*Grower practice*).

## What is the slug life cycle in numbers?

The gray field slug lives about a year, lays clutches of about 10-40 eggs and develops best near 17-20 C. All land slugs and snails are [hermaphrodites](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) and lay eggs after mating [1].

| Parameter | Value | Conditions and source |
|---|---|---|
| Eggs per clutch | 3-40 (slugs generally) | extension summary [1] |
| Eggs per clutch, *D. reticulatum* | mean 22 (range 9-49) | field, Carrick 1938, cited in [5] |
| Eggs per clutch, *D. reticulatum* | ~20 at 20 C; ~10 at 28 C | lab [2] |
| Eggs per clutch, *D. reticulatum* | 21-43 | lab [3] |
| Lifetime eggs | 217 at 20 C; 105 at 16 C | lab [2] |
| Eggs per year | up to ~500 | field estimate, cited in [5] |
| Egg hatch | 12-19 d | lab, 16-28 C [2] |
| Egg hatch | 23-27 d (hatchability 79-97%) | lab [3] |
| Hatch rate | 95% at 20 C (highest) | lab [2] |
| Juvenile period | 51-68 d | lab [2] |
| Time to maturity | 3-6 months, by species | [1] |
| Total lifespan | 216 d at 20 C; 193 d at 24 C; 170 d at 16 C; 151 d at 28 C | lab [2] |
| Best temperature | ~20 C for egg laying, development and longevity | lab [2] |
| Growth optimum | ~17-19 C, detrimental above | literature summary in [4] |
| Generations per year | 1 (lab) to 2 (UK field) | [3][4] |
| Snail clutches (brown garden snail) | up to 6 per year, ~80 eggs each | [1] |
| r_m, [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md) | no published value found | |

Slug populations are mixed-age. Spring and autumn peaks in *D. reticulatum* numbers may reflect a mixed-age population responding to good conditions rather than two distinct generations [4].

## Why do temperature and moisture matter for slugs?

Moisture decides when slugs feed and temperature decides how fast they breed. Slugs are most active at night and on cloudy or foggy days, and hide from heat and bright light [1]. In cold weather they shelter in the topsoil; hot, dry periods stop activity [1].

The gray field slug performs best near 20 C: egg laying, development and longevity peaked there in the lab, and 28 C shortened life and halved clutch size [2]. Cool, wet spring and autumn weather is slug season outdoors.

In greenhouses and polytunnels, wet floors, mulch, damp pots and drip lines keep slugs active all year (*Grower practice*). Mild coastal climates allow year-round activity outdoors [1].

## How do I scout for slugs?

Scout slugs at night and under traps, because by day they are hidden. Search with a flashlight after dark; watering the area in late afternoon draws them out [1].

Lay boards raised about 2.5 cm (1 in) on runners, or inverted melon rinds, and check underneath every morning; scrape off and destroy what you find [1]. Check daily at first, then weekly once numbers fall [1].

There is no published [action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) for slugs on cannabis. Grower practice is to act on any slug found near seedlings or transplants.

## How do I control slugs and snails on cannabis?

Control slugs and snails by combining baits, barriers, traps and habitat removal; no single method holds them alone [1]. Follow the label and local law for any bait.

**Iron phosphate baits.** Iron phosphate baits are safer around children, pets and wildlife, and some are allowed in organic growing [1]. Slugs stop feeding soon after eating them but take several days to a week to die, usually hidden [1]. Iron phosphate has been field-tested as a molluscicide [6]. Scatter baits around seedlings, not in piles.

**Other bait classes.** Ferric [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) [EDTA](https://genetixbay.com/knowledge/glossary/edta.md) baits work like iron phosphate but faster, in about 3 days instead of 7, and are not organic [1]. Metaldehyde baits are highly poisonous to dogs and cats and should be kept away from pets, children and edible plants [1].

**Bait timing.** Baits work poorly in very hot, very dry or cold weather [1]. Light irrigation before baiting encourages slugs to forage; heavy watering after baiting makes pellets mouldy [1].

**Copper barriers.** Use a copper strip at least 5 cm (2 in) tall, buried 2.5-5 cm (1-2 in) into the soil [1]. Bands on pots and planters work until they tarnish; clean with vinegar [1]. Remove slugs inside the barrier first.

**Beer traps.** Sink deep-sided containers with the rim at soil level and a lid with entry holes; they attract slugs within a few feet and need refilling every few days [1]. Sugar water with yeast works too [1].

**Handpicking.** Pick at night with gloves and drop slugs into soapy water [1]. Repeat regularly.

**Habitat.** Remove boards, debris, dense weeds and thick mulch near seedlings, and water in the morning rather than the evening (*Grower practice*, consistent with [1]).

**Predators.** Ground beetles, toads, snakes, birds and others eat slugs but rarely give enough control in gardens [1]. Penned poultry can reduce snail problems [1]. Do not release decollate snails where they are restricted [1].

## What should I not do against slugs?

Do not use metaldehyde baits where dogs, cats or children can reach them, and do not put any bait on the plants themselves [1].

Do not salt the soil to kill slugs; salt damages soil and plants (*Grower practice*).

Do not rely on beer traps alone around a field of seedlings.

## What are the common myths about slugs?

**"Salt is a good slug control."** *Myth.* It kills on contact but harms soil and plants.

**"Beer traps clear a garden."** *Myth.* They draw slugs only from a few feet away [1].

**"Iron phosphate does not work because there are no bodies."** *Myth.* Slugs die over several days, out of sight [1].

**"Copper always keeps slugs out."** *Contested.* It works only tall, clean, continuous and with no slugs already inside [1].

## Evidence

- Species, damage, behaviour and control options: *Established* (extension) [1].
- Temperature effects on *D. reticulatum* development and egg laying: *Established* in the lab [2][3][4].
- Use on cannabis: extrapolated from vegetables and gardens (*Supported*).

## Glossary terms used here

- Glossary: [slugs and snails](https://genetixbay.com/knowledge/glossary/slugs-and-snails.md)

## Sources

1. Wilen, C.A. & Flint, M.L., 2018. Pest Notes: Snails and Slugs. UC ANR Publication 7427. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7427.html
2. Kim, H.J. et al., 2009. Effects of temperature on the development and longevity of the gray field slug, Deroceras reticulatum. Korean Journal of Applied Entomology 48(4):541-546. https://db.koreascholar.com/Article/Detail/10254
3. Biology, food consumption and control of the gray garden slug Deroceras reticulatum, 2015. Annals of Agricultural Science, Moshtohor 53(4):719-726. https://doi.org/10.21608/assjm.2015.109952
4. Shirley, M., Howlett, S. & Port, G., 2020. Not all slugs are the same: variation in growth and development of the slug Deroceras reticulatum. Insects 11(11):742. https://doi.org/10.3390/insects11110742
5. McDonald-Howard, K., Williams, C.D., Jones, H. & Rae, R. A method of culturing and breeding slugs through several generations. Liverpool John Moores University repository. https://researchonline.ljmu.ac.uk/15832/3/A%20method%20of%20culturing%20and%20breeding%20slugs%20through%20several%20generations.pdf
6. Speiser, B. & Kistler, C., 2002. Field tests with a molluscicide containing iron phosphate. Crop Protection 21(5):389-394. https://doi.org/10.1016/S0261-2194(01)00120-X