Bed bugs are small, parasitic insects that feed on blood, primarily while a person sleeps. Bed bugs do possess eyes, though their visual organs are highly rudimentary compared to most other insects. Their vision is not the primary sense they use to navigate or find a blood meal, as they rely on a combination of sensory inputs to successfully find a host.
The Structure of Bed Bug Eyes
The visual organs of the common bed bug (Cimex lectularius) are reduced compound eyes. These structures are located on the sides of the insect’s head, giving them a fixed field of view. Unlike the prominent eyes of flies or dragonflies, the bed bug’s eyes are significantly smaller and simpler. These compound eyes are composed of repeating light-sensing units called ommatidia. The number of ommatidia is greatly reduced, meaning they cannot form the detailed, high-resolution images that many other arthropods can.
Function of Bed Bug Vision
The limited visual capacity of bed bugs is primarily suited for detecting changes in light intensity rather than forming detailed images. Their vision is sensitive enough to perceive movement, helping them avoid danger and stay hidden. This sensitivity to light and dark is directly linked to their nocturnal behavior, a process known as phototaxis. Bed bugs initiate movement when darkness falls, and they retreat quickly into their harborages when exposed to light. Research suggests they can detect vertical objects and differentiate between colors, even in extremely low light conditions. This limited color perception plays a role in their choice of hiding spots, as they prefer harborages that are dark colors, such as black or red.
Primary Methods of Host Detection
Given their poor image-forming vision, bed bugs rely heavily on non-visual sensory inputs to locate a sleeping host. The primary senses they employ are chemoreception (detection of chemical signals) and thermoreception (sensing of heat). The antennae serve as the main sensory organs for detecting these crucial environmental cues.
The most significant cue is the carbon dioxide (\(\text{CO}_2\)) exhaled by a host. As a person sleeps, the concentration of \(\text{CO}_2\) increases around the bed, creating a plume the bed bug can follow. Bed bugs can detect this \(\text{CO}_2\) from approximately three to five feet away, prompting them to start their host-seeking journey.
Once closer, the bed bug uses thermoreception to pinpoint the exact location of the host. They can sense body heat, detecting this thermal signature from about one foot away. The difference between the ambient room temperature and the host’s skin temperature is a more important trigger than the absolute temperature itself. They also respond to various volatile chemical compounds and odors released from human skin, which further guides them toward a blood meal.