We examined the effects of ambient temperature on the brooding behavior of male waterbugs, Belostoma flumineum Say. Male waterbugs are more likely to prematurely terminate care for small egg-pads than for larger egg-pads. Because embryogenesis and breeding season are both associated with ambient temperature, males in warmer environments may respond differently than those in cooler conditions. We studied the effects of temperature on male parental behavior by housing groups of completely and partially egg-encumbered males under different thermal regimes. Completely encumbered males rarely discarded egg-pads, regardless of ambient temperature. Partially encumbered males housed under warm ambient temperatures, however, were significantly more likely to discard the eggs than those housed under cooler conditions. These results are consistent with the hypothesis that cool ambient temperatures at the end of the breeding season elicit a terminal investment strategy.