When you see the emerged Fly Predators in their shipping pouch that is their full adult size. When the Fly Predators have emerged, the fly puparium, in which they are shipped, will still be intact, but with a little hole in it about 1/32” in diamater. One can inspect for the escape holes in the pest fly pupal case to determine if the Fly Predators have emerged.
When Fly Predators become established you will be able to see the tiny Fly Predators on moist manure piles. Although there are many small gnat like insects commonly found on the manure, the body shape, color and behavior of Fly Predators allows an experienced eye to detect them. One common misconception is that the smaller flies found around manure are “baby flies”. They are not baby flies, but different species of pest flies.
Like butterflies, Fly Predators and pest flies develop through a complete metamorphosis, from the egg, to the larval stage, and then emerging from the pupal or cocoon stage as full sized winged adults, remaining that same size for life. The pest fly’s egg and larval (maggot) stage are spent in the manure, but just before entering into the pupal stage the larva crawls up to 10 feet away from the manure and digs itself into the soil if possible to undergo its metamorphosis. It is the pest fly’s pupal stage that the Fly Predators attack. The female Fly Predator digs down and lays one or more of her eggs in the buried pest fly pupa. The female Fly Predator’s egg quickly hatches into a larva and starts feeding on the immature pest fly pupa. Then it undergoes its metamorphosis from pupal stage into full size adult. All of this takes place within the pest fly pupal case and the Fly Predator emerges to start the cycle over again. The time it takes to establish biological control is often longer than expected, but it is well worth the wait. It is not unheard of for biological control to take a season to become fully effective, but once Fly Predators are established, pest flies will never build up to nuisance levels.