In order to make clear the mechanism of the water loss through integument in the wireworms, Melanotus caudex LEWIS, the authors measured the speed of water evaporation from body, by exposing them in incubators under several conditions, and measuring the diminution of their body weights by torsion balance.<br>1. Decreasing tendencies of the curves of both the body weight and the body water, may be due to the decrease of body weight, which is equal to the evaporated volume of body water.<br>2. The speed of water evaporation from the body under a constant humidity (ca. 20% R.H.) was almost constant at 14∼20°C, and increased rapidly above 25°C. this tendency was very similar to the case of oxygen consumption. This leads us to the conclusion that any temperature over 25°C is unsuitable for growth of wireworm.<br>3. The speed of water evaporation from the body at 20°C increased linearly with the decrease of humidity. It is assumed, therefor, that there exist large areas which cannot prevent water evaporation on the integument.<br>4. By dipping the wireworm into ammoniacal silver solution, the abdomen sterna longitudinally along the basal line and also the base of legs in thorax sterna turned to black. The deoxidized parts on the integument seems to be polyphenol layers. Those parts are considered to be connected with the evaporation site.<br>5. When the leg movement stopped and worms became hard and cylindrical due to the water loss, they seemed to be dead but retained still an ability to burrow into soil when they were dipped into water for several minutes.<br>6. The curve of the evaporation speed had a shift at the midst of regression line where the ability of keeping their body water was lost.<br>Thus it became clear that the wireworms have a little ability to defend the water loss.<br>7. In winter period the speed of evaporation was about a half as that in spring period, and this tendency was almost the same to the cases of the resistivity against drying and dipping into water.<br>8. Under the condition of 20°C and about 20% R.H., the evaporation speeds of body water in other kinds of soil insects were compared with those of insects living in other environments. Larvae of Curculio dentipes and Tipula aino did not die by drying for 200min. The highest speed was that of Lacon fuliginosus, namely, 2.42 times as fast as in case of Melanotus caudex. Eevaporation speeds of both Popillia japonica and Melanotus caudex were almost the same.