Tachinid Fly: [HOW TO] Control Garden Pests With Beneficial Tachinid Flies

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The Tachinid fly is one of the “good” flies. We generally think of flies as being nothing but a nuisance.

However, you may be surprised to know of how many “beneficial” flies can help in keeping garden pests under control.

Adult Tachinid fly visiting a DandelionPin
Adult parasitic Tachinid fly visiting a Dandelion flower

Along with parasitoid wasps, parasitoid flies do gardeners a tremendous favor by killing off vast numbers of garden pests.

In this article, we discuss Tachinid flies from the Tachinidae family and share valuable information to help you make the best use of them in your yard and garden. Read on to learn more.

What Are Tachinid Flies?

There are a dozen fly families within the insect order Diptera comprised of thousands of species. Several of these species are parasitoids, and of these, the Tachinid fly is the most important.

They are endoparasites whose developing larvae live and feed inside their hosts (usually the larvae of pest insects).

These tiny flies provide important biological control of a great many insect pests. Among them:

  • Grasshoppers
  • Earwigs
  • Sawflies
  • Beetles
  • Moths and Butterflies

The Tachinid Life Cycle

Tachinid fly larvae (maggots) enter their hosts in several different ways.

In some cases, the female Tachinid fly may lay eggs on the leaves of plants consumed by the chosen host. The host eats the eggs, and they hatch in its body.

Some female Tachinid flies have an ovipositor which they use to lay eggs inside the host. Still, others glue eggs to the outside of the host’s body.

When they hatch, the maggots bore their way through the host’s skin to its interior. [source]

Once inside, tachinid maggots consume the host. They begin by eating non-essential tissue while leaving vital organs untouched.

This ensures that the host will stay alive and continue to take in nourishment until the maggots are ready to abandon the host and go their merry way.

In some instances, the maggots pupate in the host’s body. In others, the maggots emerge and drop to the ground where they pupate in the soil.

Either way, they leave the host a mere husk.

The amount of time this process takes varies from one species to another.

Some types of Tachinid flies only complete one generation annually and spend a great deal of time as pupae.

Others have shorter larval and/or pupal stages and complete their life cycle in three or four weeks.

It is also important to understand that the life cycle of the fly is entwined with the life cycle of the host. If the larval host overwinters, so does the Tachinid maggot.

It simply rests inside the host until spring arrives. In other instances, Tachinid pupae overwinter in leaf litter or soil. [source]

What Do Tachinid Flies Look Like?

There are over 1500 known species of Tachinid flies in North America, so you’re sure to have seen these them around your yard and garden, but you may not have known what you were looking at.

It can be very difficult to tell these flies from common houseflies because, unfortunately, they all look very much alike.

Look for these specific traits when identifying tachinid flies.

  • Distinguishing features: Stiff, hairy bristles protrude from the abdomen
  • Length: Ranges from 1/2 to 3/4 of an inch
  • Color: Black, gray or striped
  • Body: Stout and robust

One type of tachinid fly does stand out. This is the Feather-Legged fly (Trichopoda pennipes).

Tachinid Fly - Trichopoda pennipes up closePin

These Tachinids are bright orange. The head and thorax of this insect is covered with velvety black hair.

The legs are dark in color, and the hind legs sport a feathery fringe of black hair. The feet are yellow; the wings are black and brown, and the creatures have big, brown eyes.

How Do You Recognize Tachinid Eggs And Larvae?

Tachinid eggs are quite small in size (about 1/20th of an inch in length). They are oblong and may be either white or gray.

You may see them on the leaves of plants or on the bodies of hosts, such as leaf eating caterpillars and beetles.

The maggots are not usually visible as they stay inside the host until they are ready to emerge and pupate. Some pupate inside the host.

The pupae are very small, oblong cases and are dark reddish brown. You may encounter them in the soil as you dig in your garden.

What Does The Adult Tachinid Fly Eat?

While the maggots feast on the larvae of garden pests, the adult flies perform an important duty as pollinators.

They feed on pollen and nectar and are especially fond of umbelliferous plants (e.g. dill, carrot and herbs in general).

They also favor composite flowers such as Rudbeckia hirta (Black-Eyed Susan), Asters and a wide variety of other flowering plants. Additionally, they eat aphid honeydew.

For this reason, allowing aphids to remain in a non-crop area of your garden helps attract and support your tachinid fly population.

In fact, just as you would plant a butterfly garden to attract butterflies, you may also wish to plant a tachinid garden to attract and conserve these valuable, beneficial insects.

Provide them with a diverse collection of plants with small flowers, such as:

Allow native plants, such as wild carrots and sweet clover to flourish in parts of your yard and garden.

In addition to taking steps to attract Tachinids, be careful to conserve them.

Avoid the use of pesticides, and if you see caterpillars carrying white eggs on their backs, be sure to leave them alone.

These may be the eggs of tachinid flies or parasitoid wasps.

Either way, you should leave them in place to grow, pupate and metamorphose into beneficial insect garden helpers.

Are Tachinid Flies Entirely Beneficial?

These tiny insects are very helpful in the garden because they kill huge numbers of pests.

With the decline of bee populations these days, Tachinid flies are extremely important as pollinators in the garden and in nature.

Because humans have nothing of interest to offer them, Tachinids do not bother people.

They are far too busy pollinating plants, gathering nectar and seeking out pest insects to pay any attention to us.

Having a healthy population of tachinid flies is extremely helpful in reducing the numbers of pests in your garden, including:

Usually tachinid larvae parasitize these pests during the immature stages of life; however, some types target adult insects.

The Feather-Legged fly especially targets leaf-footed bugs (i.e. squash bugs and stink bugs). The Winsome Fly (Istocheta aldrichi) targets mature Japanese beetles.

Unfortunately, they also target some beneficial predatory insects, such as the praying mantis and are indiscriminate regarding the types of caterpillars they choose as hosts.

Do Tachinid Flies Bother Beneficial Butterfly Caterpillars?

According to the University of Georgia’s monarch parasite website, these flies frequently target and kill monarch caterpillars. [source]

If you try to keep a butterfly garden, these otherwise beneficial flies may be problematic.

One solution may be to maintain diversity in the garden as described above.

Plant lots of different types of flowers and veggies to attract a wide variety of insects so the Tachinid flies will have plenty to choose from.

Avoid using pesticides in the garden, and encourage all manner of predatory and parasitoid insects to attain a natural balance.

If you are only keeping a patch of milkweed for monarchs, you are setting up a monocrop situation.

This is bound to result in trouble with Tachinid flies targeting your treasured caterpillars.

Watch For These Types of Tachinid Flies In Your Yard And Garden

Because there are so many different types of tachinid flies, you are sure to encounter them as you go about your business in your yard and garden.

Here are a few you may encounter:

Voria ruralis: This type of parasitoid fly is especially effective against moths in the Pyralidae and Noctuidae family. It makes short work of cabbage looper caterpillars.

The female adults lay one or more eggs in the host. The eggs hatch quickly, and the maggot(s) set to work gobbling up the host.

When the host has died, the maggots emerge, fall to the ground and create dark reddish/brown, oblong pupa cases about a third of an inch long. [source]

Lydella thompsoni: This type of fly specializes in doing away with the European corn borer and is in commercial use in corn fields around the US.

Having these flies in residence makes corn growing far easier, more successful and more productive.

Myiopharus doryphorae: This species prefers Colorado potato beetle larvae as hosts. The female fly deposits eggs inside the beetle larvae where the maggots develop. When the beetle larva dies, the maggots emerge and pupate.

The Myiopharus doryphorae fly also favors squash bugs as hosts. The female fly lays eggs on the surface of the adult insect’s body.

The maggots hatch and bore into the insect. Once inside, they consume the bug’s innards until they are too big to stay. At this point, they emerge, drop and pupate and the bug dies.

Trichopoda pennipes: This is the colorful, feather-legged fly. It specializes in parasitizing true bugs, squash bugs and stink bugs.

The female fly may lay eggs on the surface of the bodies of either adult bugs or their nymphs.

Maggot hatchlings burrow directly into the host’s body, consume it from the inside out and then leave to pupate. The bug or nymph dies.

Erynnia tortricis: Moth and butterfly caterpillars are the preferred hosts of this species of fly. It is effective against these species:

  • Oblique banded leafroller
  • Omnivorous leafroller
  • Oriental fruit moth
  • Peach twig borer
  • Sunflower moth
  • Pink bollworm
  • Codling moth
  • Amorbia

The Erynnia will also go after other types of caterpillars, so if you are trying to keep a butterfly garden, be sure to maintain diversity in plant species to attract lots of other choices in hosts.

Erynnia tortricis females attach eggs to the thorax or head of the host caterpillar, and the hatched maggots bore into the caterpillar’s body.

You can recognize a parasitized caterpillar because of a Y-shaped bulge (parasite spiracle) protruding from under the host pupa’s wingpad tips. [source]

Where Do You Buy Tachinid Flies?

It’s hard to find a place to buy these flies, but the good news is you probably already have some!

You can find tachinid flies all around your yard and garden. However, because so many look like houseflies, you may not realize them.

One way to determine whether a fly is a common housefly or a tachinid is to observe its behavior.

For example, if you see a fly in your veggie garden pestering and laying eggs on squash bugs, you can guess that it is a feather-legged tachinid fly.

Flies that stay close to the grass or in the shrubbery (where Japanese beetles tend to hang out) are probably Istocheta aldrichi tachinid flies.

Even if you don’t see flies, watch for caterpillars carrying clutches of tiny, white, oblong eggs. That’s a dead giveaway that tachinid flies are already hard at work for you.

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