Adult yellow mealworms are shiny, sturdy, dark brown to black beetles and measure around 16 mm (14–18 mm) in length. They are the biggest insect pests to infest whole and ground grains. Males are usually smaller and slimmer than females.
Darkling beetles are small and black, but on close examination their shells reveal a wide variety of shapes and textures. This makes them just as interesting to look at as other, more colourful beetles. Darkling beetles are 3 to 4 cm long.