Location and Uses
Hyrule Compendium Entry
These Restless Crickets can be found Just about anywhere by cutting grass with any sharp sword. When found in grass, they will hop away 2-3 times before flying off and disappearing. you can also find them naturally in Hyrule Field or East Necluda. Although you can find quite a few of them in Hyrule Field and East Necluda, cutting grass is very efficient especially because you can also find Fairys and Hightail Lizards.
There is a quest called "A Gift for My Beloved" where you have to collect 10 Restless Crickets for Manny (Breath of the Wild). Upon collecting the 10 Crickets, you must return to Manny (Breath of the Wild) and he will take them, and give you your reward of 100 Rupees.