Dovetail mate

The queen occupies a square diagonally adjacent to the king and gives check. From there it controls almost all of the king's immediate surroundings. The two nearby squares left outside that coverage are occupied by the defender's own pieces, creating the visual shape of an open tail.

Two blockers for a diagonal queen

8

7

6

5

4

3

2

a1

b

c

d

e

f

g

h

The queen on f4 checks e5 and currently attacks d4, e4, f5, and f6.

The diagonal defines the net

In the static position, the queen on f4 checks the king on e5 and attacks d4, e4, f5, and f6. The black pawns occupy d5 and e6, and the white king on g3 protects the queen. d6 is not attacked while the king remains on e5; if it tries to move to d6, it vacates e5, opens the f4-e5-d6 diagonal, and makes the destination illegal.

1. The queen on f4 checks e5 and currently attacks d4, e4, f5, and f6.
2. The black pawns on d5 and e6 occupy the two neighboring squares that form the pattern's tail.
3. The white king on g3 protects the queen on f4, so the black king cannot capture it.

The queen must be protected. Because it stands next to the king, the king could capture it if that square were safe. It is mate only when neither the king nor another piece can capture the queen and no other legal response to the check exists.

The identities of the two blocking pieces do not matter. The geometry does: a diagonally adjacent queen, two exits closed by the defender's own pieces, and enough support to make the queen untouchable. The classic form has the king on an interior square, where those two exits exist. It resembles swallow's tail mate, but there the queen is beside the king on the same row or column rather than on a diagonal.