Usually the males are smaller than the females...
No females slightly larger than male
On the ventral side and almost to the tail you will see a large ( relatively ), dark swelling with two small projections. This is the female. Males do not have this area.
Well what I heard that if one is litter its gril and if one is darker it,s a boy.
The females are slightly larger. Their mating behaviors are quite different. The males [like most other males] tend to make a chase.
If it is smaller it is a male if it is bigger it is the female
You check and compare your meal worm with another 2 or 3!
Only a microscope can tell you fools