Final answer:
The largest challenge to survival faced by insects based on their size is their ability to fly. Larger insects have a harder time sustaining flight due to their size and weight.
Step-by-step explanation:
The largest challenge to survival faced by insects based on their size is their ability to fly. Flight is a key reason for the success of insects, allowing them to escape predators, and find food and mates. However, flying requires a lot of energy, and larger insects have a harder time sustaining flight due to their size and weight. In addition, the small size of insects makes them vulnerable to predation and environmental conditions, such as temperature and humidity.