 Therefore, a majority of water lost to the atmosphere occurs via the air-filled tracheae.To help reduce water loss, many insects have outer coverings to their tracheae, or spiracles, which shut when open respiration is unnecessary and prevent water from escaping.Insects at a greater risk for water loss face the challenge of either a depleted oxygen supply or desiccation, leading to an adaptive increase in tracheal volume in order to receive more oxygen.