Thanks, dxb. John Clare wrote a poem about one, I see:

In the cowslip pips I lie,
Hidden from a buzzing fly,
While green grass beneath melies,
Pearled with dew like fishes eyes
Here I lie a clock-a-clay,
Waiting for the time of day.

While grassy forest quakes surprise,
And the wild wind sobs and sighs,
My home rocks as like to fall,
On its pillar green and tall,
While the patt'ring rain drives by,
Clock-a-clay keeps warm and dry.

Day by day and night by night,
All the week I hide from sight,
In the cowslip pips I lie,
In rain and dew still warm and dry,
Day and night and night and day,
Red, black spotted clock-a-clay.

My home shakes in wind and showers,
Pale green pillar topped with flowers
Bending at the wild wind's breath,
Till I touch the grass beneath,
Here I live, lone clock-a-clay,
Watching for the time of day.

Golly, it sounds like it ought to be clock of clay, which makes no sense. Does rhyming slang go back that far?
Something-something fly away?