What is eating holes in my lettuce at night?

Short answer: Slugs or snails are a plausible cause of irregular, ragged holes in lettuce, especially where conditions are damp and shaded. Look for the animals after dark or in cool, wet periods and for silvery slime trails before deciding on control measures.

How to decide

Confirm the culprit

Check leaves near soil level, underneath pots or boards and in sheltered, wet spaces. UConn notes that slugs and snails often feed at night and hide during daylight. Similar-looking holes may have other causes, so don't assume every damaged leaf means slugs.

Make the bed less hospitable

Remove unnecessary ground-level debris and hiding places, improve airflow where possible, and avoid excessive mulch immediately around vulnerable lettuce. Keep irrigation appropriate for the plants rather than maintaining constantly damp hiding areas.

Use targeted physical controls first

Inspect during active feeding periods and remove confirmed slugs by hand if practical. Boards or similar shelters can help concentrate them for monitoring and collection. If considering bait, follow the current product label and prevent access by pets and wildlife.

Important: Do not automatically apply pesticides or homemade leaf sprays based on holes alone. Confirm the pest and select controls appropriate to edible crops and the site.

Sources and further reading

UConn Home Garden Education Office — Slugs and Snails