A female lady bug is slightly larger than a male lady bug, and if a layperson happens upon ladybugs mating, the partner on top is the male. However, most laypeople cannot readily discern the difference between a male and female ladybug.
The reality is that an entomologist, a scientist that studies insects, is challenged with identifying the sex of a ladybug, even with a high-powered microscope. No matter the sex of a particular ladybug, the insect is called a "ladybug." More than 5,000 different species of ladybugs exist around the world, with more than 500 found in the United States.