Your sentence is grammatically correct.
Original: Echidnas hide in the dirt and show only their spiky backs to stay safe.
Slightly improved (optional): Echidnas hide in the dirt, showing only their spiky backs to stay safe.
For one echidna: An echidna hides in the dirt and shows only its spiky back to stay safe.
Why this is correct (simple):
- 'Echidnas' means more than one, so we use the plural verbs 'hide' and 'show'.
- The sentence has a clear subject and verbs, and it ends with a period.
- Using 'showing' with a comma is another correct way to connect the two actions (hiding and showing).
Great job — the sentence is clear and easy to understand!