Where to catch Orthworm

In Paldea (Scarlet & Violet)

• Asado Desert — Walk
• East Province (Area Three) — Static Encounter, Walk

In Kitakami (Scarlet & Violet – The Teal Mask)

• Apple Hills — Walk
• Kitakami Wilds — Walk
• Oni Mountain — Walk
• Oni's Maw — Walk
• Paradise Barrens — Walk
• Reveler's Road — Walk
• Wistful Fields — Walk

Orthworm — full Pokédex entry