Ecological Indicators The presence of dragonflies can reveal changes in the water ecosystems more quickly than studying other animals or plants. In fact, from the nymph to the adult stage, the dragonfly has a significant, positive ecological impact. Dragonfly eggs are laid and hatched in or near water, so their lives impact both water and land ecosystems. Once hatched, dragonfly nymphs can breathe underwater which enables them to eat mosquito larvae, other aquatic insects and worms, and even small aquatic vertebrates like tadpoles and small fish and in the air. Adult dragonflies capture and eat adult mosquitoes. Community wide mosquito control programs that spray insecticides to kill adult mosquitoes also kill dragonflies.
Dragonflies indicate positive ecological impact as-

Options

A. The presence of dragonflies indicates polluted water.
B. Dragonfly nymphs selectively eat mosquito larvae
C. They help to decrease the probability of diseases spread by vectors.
D. Dragonfly do not cause any harm to beneficial species.

Answer

c

Explanation

They help to decrease the probability of diseases spread by vectors.