Do dragonflies spend their larval stage on water?
Yes, they do for 2 to 3 weeks!
It depends on the insect. Some insects such as mosquitoes/dragonflies/damselflies can spend their larval stage in the water of ponds and streams. Adult forms of insects such as ladybugs will seek shelter under rocks, loose bark on trees and inside the walls of houses. Other insects such as Monarch butterflies can fly hundreds of miles south to spend the winter in Mexico, and return back to the U.S. next spring.
Frogs and toads are amphibians, which means they live their lives both in water and on land. Typically, frogs breed and spend their juvenile (or "larval") stage in the water, then spend some or virtually all of their adult lives on the land. Frogs and toads are distinguished from salamanders (which are also amphibians) by the fact that adults do not have a tail.
Dragonflies are insects and during their larval/nymph stages they live for several years in/on the bottom of freshwater pools or lakes. Here there may be many of them but they live as individuals. Come summer and the mature nymphs crawl out of the water and transform into adult dragonflies with wings. In this stage they are predatory flying insects that again live alone. However, during the adult phase they will couple and mate with another…
Because they spend all their developing phase underwater. In their larval stage, they absorb oxygen through gills - In their short adult life, they spend their time flying above the water, and thus breathe air. When they crawl out of their skin, they have completed the change from larva to adult - much like a caterpillar changes into a butterfly. The only difference is - they don't go through a pupae stage.
Yes. A dragonfly larva lives in the water, feeding on small animals from water fleas to stickleback, and breathes through gills at the back end. To become an adult it climbs out of the water and molts into the winged form. You might have seen the larval skins on rocks and plants at the water's edge!
How can putting a layer of oil o the surface of the water will help to control the populations of mosquitoes?
Frogs are amphibians. Frogs have wet, permeable skin without scales, lay jellylike, non amniotic eggs in water, have a fully aquatic, gilled larval stage, and most cannot spend much time out of water. By contrast reptiles habe dry, scaly, waterproof skin, leathery amniotic eggs that they lay on land or hatch internally, and have young that look like small adults. Most can stay out of water indefinitely.
Female dragonflies lay eggs in or near water. The eggs then hatch into nymphs. While in the nymph stage they eat mosquito larva. Most of the dragonfly's life is spent in the nymph form, beneath the water. After three to five years, the larva metamorphoses into an adult. The adult stage can last as long as five or six months.