A device (10) for detecting the presence of light averse insects, such as termites, is in the form of a peg (11) having a cavity (14) into which termites may enter when the peg is installed in the ground or other area where the presence of termites is to be detected. The cavity may include a termite bait. A light sensor (25) is located in the cavity, and has an output which is responsive to the detection of light. The light sensor operatively receives light from a light emitting device (LED) (23) only through a narrow passage extending through the peg from the LED (23) to the cavity (14). The passage is adapted to be at least partially blocked by the light averse insects to shield the cavity, and hence the light sensor means, from light from the passage. When the light sensor means (25) does not detect sufficient light, an electrical circuit (22) connected to the output of the light sensor means triggers an alarm light (26) to signal an alarm or alert condition.