When larvae are nearly mature, place corrugated paper, rough burlap or crumpled paper toweling in the cage. Let adults emerge before disturbing. Avoid too many adults in the cage because they can eat eggs and reduce the population. Harvest the larval fish bait just before pupation begins or as needed. In a short time you will have all the mealworms you can use.
Size is largely a matter of feed and temperature.
Care must be taken not to freeze them. Observation is the secret of raising mealworms. All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status. Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.