Dragonflies by Lake Area

Dragonfly Density per Lake Area

In freshwater bodies that are still in good shape, dragonfly density (order Odonata) tends to sit somewhere between 1 and 3 individuals per square metre of water surface through the warm months. For a rough first number, use N = surface area (m²) × density. From there you adjust for water quality, how much vegetation is around, and whether there is enough prey to support the population.

In their underwater naiad stage, dragonflies are aggressive predators. They eat mosquito larvae, tadpoles and small fish, which makes them an important check on the food web. Brazil has roughly 830 described Odonata species, and you find the most variety in the Amazon and the Atlantic Forest.

Applications

Dragonflies are a common bioindicator of water quality. Whether they show up at all, and how many species you count, feeds into wetland conservation work run by ICMBio and CEMAVE. The same readings help guide the ecological restoration of ponds, lakes and water bodies inside cities.

FAQ

Why are dragonflies considered bioindicators? Their larvae need water that is rich in oxygen and low in pollution. When numbers fall, it usually points to eutrophication, contamination or too much sediment building up.

How long do dragonflies live? The naiad stage can run for months or even years underwater. The winged adult, by contrast, usually gets only a few weeks, and spends most of that time reproducing.

What is the difference between a dragonfly and a damselfly? Dragonflies (Anisoptera) are bulkier and hold their wings spread out when resting. Damselflies (Zygoptera) are thin and fold their wings back over the body.