Rhynchophorus ferrugineus is a tropical pest of palms that has recently invaded Japan, where winter temperatures fall below 0˚C. Because activities of the weevil at temperatures <13˚C are extremely limited, it appears difficult for them to overwinter in Japan. However, the temperature of palm tissues damaged by this weevil has been observed to be higher than air temperature. Here, we looked for the cause of this temperature increase. First, we measured the temperature of damaged palm tissues and showed it to be between 30˚C and 40˚C, even in winter. Next, we isolated yeasts from the body of weevils and infested palm tissues and obtained 36 yeast strains, mostly Candida tropicalis and C. ethanolica. Then, we analyzed the soluble sugar composition in palm tissues and found that it included glucose, sucrose, and fructose. Because at least C. tropicalis can ferment some of these sugars, the temperature increase may be attributed to fermentation of microbes, including yeasts.