Sentinel species are organisms – animals [and plants], used to detect risks to humans by providing advance warning of a danger – environmental hazards. Some animals can act as sentinels because they may be more susceptible or have greater exposure to a particular hazard than humans in the same environment.
Insects [especially bees, bumble bees, butterflies, moths] are therefore very good bioindicators whose response within an environment, especially change in conditions and presence of pollutants, provides a more general information on current and future environmental quality. Why? Because they are extensively studied across time, have relatively short life cycles therefore respond rapidly to changes in ecosystem and climate variations.
The major role of insects is pollination and a very important part in the food chain. But number of insects is in a severe decline. We need to protect them as they protect us.