Why do we use the simile, " merry as a cricket?

"Because, quitting its summer abode, about the end of August, and fixing its residence by the fireside of kitchens or cottages, the cricket is as merry at Christmas, as other insects in the dog-days.

Herrick, among the pleasures of a country life, quaintly sings to his brother, Yet can thy roof maintain a quire,

Of singing crickets by thy fire;

And the brisk mouse may feast herself with crumbs,

Till that the green-eyed kitling comes.

The grasshopper and cricket race effect their well-known and often wearisome chirpings by grating their spiny thighs against their rigid wings.