Some types of flies might be a bother with their stinging bite and buzzing voice. The Tachinid or “Diptera” species, on the other hand, is well worth inviting to your organic garden because of its ferocious appetite for garden pests such as Japanese beetles and grasshoppers.
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
There are more than 1,300 North American species of parasitic flies. Most resemble robust houseflies, but with short, bristly hairs on their rear ends. Tachinid flies are gruesome parasites of other insects. They employ a variety of tactics, with a common practice being to glue an egg onto another insect, so that the tachinid fly maggot can consume it as food. Other species of tachinid fly may lay mini-eggs on foliage being eaten by insects, which hatch in the insects’ bellies, or they may inject their eggs directly into another insect’s body with a sharp ovipositor.
Egg and larval development happen quickly in tachinid flies. Indeed, a quirk of many species is their ability to lay eggs that hatch almost immediately, or even before they are laid. Many tachinid fly species pass from the early stages to adulthood in just three to four weeks. If the host also moves through life stages quickly, several generations can be produced in one garden season. At the end of the season, some tachinid flies overwinter in leaf litter, while others spend winter inside the pupal cases of their victims.
Tachinid flies feed on caterpillars, beetles, bugs, earwigs and grasshoppers. Garden pests likely to be impacted by tachinid flies include gypsy moths, cabbage worms, Japanese beetles, armyworms, cutworms, sawflies, codling moths, peach twig borers, pink bollworms, tent caterpillars, leafrollers and squash bugs. Adult tachinid flies feed on nectar, pollen and honeydew.
Tachinid flies can easily feed on the nectar of Queen Anne’s lace and other members of the carrot family. Attract tachinid flies by growing plants that bear umbels of flat florets, including carrots, cilantro, dill, coriander, buckwheat and sweet clover. Anise hyssop (Agastache) is also a favorite of tachinid flies.
More information about tachinid flies is available from the University of California, North American Dipterists Society, and the Agricultural Research Service.
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I realize that Tachinid flies fall into the "beneficial pest" category, but not in my case. Tachinid flies are killing 100% of the Monarch butterfly caterpillars in our butterfly garden. Are there any natural means to discourage them from parisitizing our Monarchs?