There are many insects that are beneficial to the garden. These helpful creatures aid in decomposing plant material, pollinating crops and devouring pests which are harmful to your garden.
Parasitic wasps - lay their eggs in the bodies of numerous pests, feeding off of them and eventually killing them.
Centipedes & millipedes - wipe put all sorts of soil-dwelling pests, such as slugs, while millipedes help break down organic matter.
Assassin bugs - help suppress harmful bug populations by feeding on flies, harmful beetles, mosquitoes, and caterpillars.
Aphid midges - prey on aphids.
Hover flies aka flower flies or Syrphids - adult hover flies are pollinators and its larva will devour approximately 400 aphids during its development.
Ladybugs - both adults and larvae prey on aphids and other soft-bodied insects as well as their eggs.
Pirate bugs - especially fond of thrips, spider mites, and small caterpillars. Plant goldenrod and yarrow to attract them.
Green lacewings - larvae feed on aphids as well as mealybugs, scale, moth eggs, mites, small caterpillars
Here's a helpful poster for reference, prepared by Heather Holm:
Download poster :