Depending on the research question, select pellets individually or choose random.
If quantitative information about the diet is needed (i.e. how much bugs did my bat eat) the pellets must be weighed. To make sure all pellets are completely dry (no miniscule droplets of water or condensation from freezer) they have to be dried beforehand.The drying process may take 24 hours, or the pellets can be placed in a stove for half an hour at a temperature of 60oC. This temperature was chosen to avoid the melting and deforming of the plastic petri dishes.
When the pellets are dry, one can determine the dry weight of each pellet. This can be done with an accurate balance (0.00001 gram) , be careful weighing the pellets in their container, as each container can have marginal variations in weight.
After the drying process the droppings need to be softened, to be able to examine them. This can be done in water, but this will enhance the smell of the pellets. Or dissolve the pellets in a solution of glycerol that was diluted with alcohol 70%. The glycerol itself is viscous, this will prevent small insect fragments from moving.
After 12 hours the pellets are softened and can be unraveled by gently pushing and pressing on the pellet with a non-sharp and bend needle. Make sure the needle is cleaned when starting on a new sample, to prevent the transfer of fragments into another dish. If the pellets are still hard, leave them alone again to soften some more over time.