Which group of insects are considered perennial indicators?

Mayflies and stoneflies are recognized as perennial indicators due to their life cycle and habitat preferences that reflect the health of freshwater ecosystems. These insects are sensitive to changes in water quality and are commonly found in clean, oxygen-rich streams and rivers. Their presence or absence can provide valuable information regarding environmental conditions, especially in relation to pollution levels and habitat integrity.

Mayflies, for instance, require good water quality to thrive, and their nymphs live in aquatic environments for a year or more before emerging as adults. Stoneflies share similar habitat preferences, and their life cycles also hinge on clean water sources. Because they are dependent on specific environmental conditions, monitoring their populations can help scientists assess the health of freshwater ecosystems over time.

In contrast, other groups mentioned may not have the same level of sensitivity to environmental changes, making them less reliable as perennial indicators of ecological health.