Although bed bugs love to feed on human blood, they do not have eyes that see like humans. These parasitic creatures have what is called a compound eye structure. It is thought that they do not see in color, that they visualize in black and white.
The eye of a bed bug is made up of hundreds of lenses called facets that fit together in a hexagonal structure. An easy way to imagine what this bug eye looks like is to think of a honeycomb that is conical in shape and not flat. It’s like a soccer ball, but on a smaller, more complex level. The individual facets consist of two lenses, one on the surface and one on the inside. Bed bugs’ double-lens eye structure allows them to see in 3-D. All these facets fitted together build the eye of the parasite. These facets are connected to tubes that focus light onto a central structure called a rhabdome. The rhabdome is sensitive to light and directs information via an optic nerve to the insect’s brain.
Each individual facet in the bed bug’s eye sends a different image to its brain. When all these images are processed and put together, a mosaic is created. This three-dimensional mosaic is the bed bug’s way of seeing its human host. It is not known whether, as the bed bug moves, the image it sees is updated in its entirety or it takes microseconds for each lens to update the visual information. If the vision of this parasitic insect is updated lens by lens, it would see a constantly updating image. This view would be like looking through a kaleidoscope with 3-D glasses.
Bed bugs come out at night or in the dark to feed on their human hosts for a couple of reasons. One of the reasons is because at night when you are sleeping in your bed, you will not feel like they are crawling on you and biting you. Another reason could be that these bloodsuckers have light-sensitive eyes that allow them to see better in the dark. These compound eyes can also pick up a heat signature from the human body. This is the reason why most bed bug bites occur on the center of mass part of your body. Its heat signature is warmer on the torso, legs, and arms than it is on the fingers and toes.
Humans can have constantly updating color vision, while bed bug compound eyes see in black and white. Your eyes aren’t constantly updating the entire image at once either, but they can see very well to do the job they’re best at. That job is to find a human host on which to feed on their blood.