The number appears to be constant in each species.

How does the insect know when her task is fulfilled?
Not by the cell being filled, for if some be removed, she does not replace them.

When she has brought her complement she considers her task accomplished, whether the victims are still there or not.

How, then, does she know when she has made up the number 24?
Perhaps it will be said that each species feels some mysterious and innate tendency to provide a certain number of victims.

This would, under no circumstances, be any explanation; but it is not in accordance with the facts.