Snake under deck what to do is a common homeowner search because decks combine shade, boards, stairs, lattice, stored items, and foundation edges into one low-visibility space. The safest first response is to stop treating the area like normal storage or pet access and treat it like hidden wildlife habitat until the snake's position is clear.
Do not crawl under the deck, pull lattice by hand, reach for toys, or send a dog under the stairs to investigate. Move children and pets away, stand outside the likely exit routes, and watch whether the snake is under stair treads, behind lattice, beside stored furniture, or moving along the foundation line.
Decks attract snakes indirectly through structure and food-chain activity. Cool shade, damp soil, insects, frogs, lizards, and rodent scent can make the deck perimeter more useful than open lawn. If there are gaps under steps, loose skirting, stacked pots, or leaves against the posts, the snake may have several protected routes you cannot see from one angle.
If a safe photo is possible, take it from outside the deck footprint without lying down or reaching through gaps. Do not remove boards or bang on the deck to force movement. Startling the snake often makes it disappear into a tighter void and leaves you with less certainty about where hands, feet, and pets should avoid.
SerpentID can help compare likely species from a stable photo, but a partial view under deck boards often deserves a conservative response. If the app suggests a venomous match or the snake remains in a space you must access, contact local wildlife help. Afterward, reduce clutter under the deck, repair loose skirting, trim dense vegetation, and keep pet paths away from blind crawl spaces.