Hens require eggstra calcium to help them lay strong, healthy eggshells. Due to the lack of quality feeds and "treats" on the market prior to 2015, chickens have needed additional calcium sources like oyster shells to avoid thin eggshells.
Unless you are feeding a zero-dust feed, it's common to have a feed where the calcium and other essential nutrients floats to the bottom as dust (making it impossible for any chicken to eat it). This creates more waste and results in lower quality nutrition for chickens. This often means thin eggshells.
Black soldier fly grubs are the only insect in nature to have a 3-1 calcium to phosphorous ratio for optimal nutrient absorption. In other words, your flock will receive the full nutrients, without needing extra calcium supplements like oyster shells.
Don't miss this! Black soldier fly grubs and mealworms are not interchangeable. They are two different insects with different levels of nutrients for your flock. Grubs have over 50x more calcium than mealworms to help chickens lay higher quality eggshells. Mealworms also require oyster supplements while grubs do not. You can learn how grubs and mealworms compare here.