The lesser mealworm, Alphitobius diaperinus (Panzer), is a carrier of Campylobacter spp. in poultry facilities; however, the beetle's importance in the epidemiology of campylobacteriosis is not known. A series of laboratory experiments were designed to test the vector and reservoir competence of the lesser mealworm for Campylobacter jejuni. In the first experiment, C. jejuni was swabbed onto the outer surface of adult and larval beetles to determine how long bacteria can survive on the beetles' exterior. Next, adult and larval mealworms were allowed to drink from a solution containing C. jejuni and the duration of internal carriage was monitored. For the third experiment, beetles drank from a Campylobacter suspension and the duration of fecal shedding of bacteria was determined. In the last experiment, 3-d-old chickens were fed either one or 10 infected beetles, and cloacal swabs were tested periodically for Campylobacter. C. jejuni was detected on the exterior of larval beetles for 12 h, from the interior of larvae for 72 h, and from the feces of larvae for 12 h after exposure. Ninety percent of the birds that consumed a single adult or larval beetles became Campylobacter-positive, whereas 100% of the birds that consumed 10 adults or larvae became positive. These experiments demonstrated that the lesser mealworm could acquire and harbor Campylobacter from an environmental source. We found that the lesser mealworm was capable of passing viable bacteria to chickens that consumed the beetle. The beetle should be included in attempts to maintain Campylobacter-free poultry facilities.