The Back Beach beetle (Bembidion (Zecillenus) tillyardi) is a small critically endangered species of ground beetle, found only in the intertidal sand of Back Beach, a small sandspit near Nelson, New Zealand.

[2] It occurs in 1–2 mm wide burrows at the high-tide mark in sandy sediment without too much mud.

[3] When the Waimea River carved a new outlet through the bank in 1875, sand began to accumulate in the Tahuna area, with dunes building up at the start of the 20th century, and the Back Beach inlet appearing by 1914.

[4] In recent years, the main channel in the Waimea estuary has been moving eastward, gradually eroding away Back Beach.

B. tillyardi's habitat is also threatened by sea level rise and the depositing of fine sediment that the beetle cannot tolerate.