It is a common misconception that bedbug infestations can be detected by smell, or by the presence of small red blood stains. The most reliable way of detecting bedbug infestations is through the presence of bedbug feces, which can stain bedding. You probably will find a group of bedbugs huddled together surrounded by black stains on your mattress.
Though bedbug bites can occur singly, they often follow a distinctive pattern of a linear group of three bites, sometimes macabrely referred to as “breakfast, lunch and dinner”. These patterns of bites are caused when a bedbug is disturbed in feeding by a person moving, and then the bedbug resumes feeding. Bedbug bites also often occur in lines marking the paths of blood vessels running close to the surface of the skin. The effect of these bites on humans varies from person to person, but often cause welts and swelling that are more itchy and longer-lasting than mosquito bites. Some people, however, have little or no reaction to bedbug bites. Those whose bodies do not initially react may subsequently develop symptoms, however, due to an allergic reaction caused by the development of antigen. Bedbugs never crawl under one’s skin and markings implying this may be signs of other skin infections or a severe allergic reaction to bedbug bites.
For more information, visit: Health Canada | Effective Control of Bed Bugs