Its large size and the markings on its wings make it a conspicuous species; a hovering Megaloprepus has been described as a "pulsating blue-and-white beacon".

The naiad is a top predator in its tree-hole habitat, feeding on tadpoles and aquatic insects, including the larvae of mosquito species that are vectors of human disease.

[4] The three leaflike caudal lamellae at the end of the abdomen, which serve as gills, are broad and elaborately folded, an adaptation to intermittent low oxygen availability in its habitat.

[7] They are not territorial, but larger individuals displace smaller ones; their aggressive behavior includes raising and swinging the caudal lamellae and striking with the labium, the hinged, extensible lower "lip" that odonate naiads use to catch prey.

It forages in areas that receive direct sun, such as the gaps created by fallen trees or branches; the light helps it avoid becoming entangled.

Large tree holes also give Megaloprepus better chances of surviving to emerge if one of its slower-growing relatives in genus Mecistogaster is already present.

The structure of the penis suggests that, as with many other odonates, male Megaloprepus are able to displace sperm from previous matings, ensuring the paternity of the eggs.

For their part, females do not choose mates based on size, and will sometimes remate with smaller males who cannot take over a territory and instead adopt a satellite position nearby.

[20] Megaloprepus avoids flying across large clearings that lack shaded perches, and has poor flight endurance, achieving a maximum distance of less than 1 km when experimentally released over water.

Since Megaloprepus reduces the number of adult mosquitoes that emerge from tree holes it inhabits, and some of the species it preys on are important disease vectors, its conservation may have human health implications.