You can see the strength of your eggshells by the way they crack. A shell that breaks in a crisp, clear line and measures about 0.3 mm thick is a good indicator of a healthy hen.
While calcium will help your chickens produce stronger eggshells, it’s important to maintain a calcium to phosphorous ratio of 3:1 to absorb the nutrients.
Black Soldier Fly grubs are the only insect with this optimal ratio, and will not require additional calcium supplements such as oyster shells. A small handful of grubs per chicken daily will help your chickens lay thicker eggshells and prevent egg-binding, a potentially fatal condition.