#### Answer

Between $-6$ and $-5$.

#### Work Step by Step

Note that:
$25 \lt 26 \lt 36$
For negative numbers,
$-36 \lt -26 \lt -25$
Thus,
$-\sqrt{36} \lt -\sqrt{26} \lt -\sqrt{25}
\\-6 \lt -\sqrt{26} \lt -5$
Therefore $-\sqrt{26}$ is between $-6$ and $-5$.