Question

what do dragonflies prefer to eat

Answer 1

Because they survive by eating only

Answer 2

Here is ur answer ji
Adult dragon flies mostly eat other flying insects, particularly midges and mosquitoes.
They also will take butterflies, moths and smaller dragon flies. The larvae which live in water, eat almost any living thing smaller than themselves.
Usually they eat blood worms or other aquatic insect larvae.
Hope it helps you out ji
Thanku ji