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5 Beneficial Insects for Farms and Gardens

By Raven Larcom on 24. October 2024
Raven Larcom

In the world of agriculture, the spotlight often shines on pollinators and the wonderful yields of their labor: blooms, fruits, and vegetables. Yet, hidden among the leaves and soil, there’s a much bigger community at work keeping our food systems healthy.

 

What is a beneficial insect?

Beneficial insects prey upon and parasitize crop pests, recycle nutrients, help decompose plant and animal waste, aerate and improve soil quality, and support other wildlife in vast food chains. We most often use the term to refer to insects, and other arthropods such as spiders, that contribute to pest control.

 

What do beneficial insects do?

So how do beneficial insects control pest populations? Simply put, they eat them.

Beneficial insects can be divided into two primary groups: predators and parasitoids. Predators will actively hunt, kill, and consume pests. Parasitoids are specialist parasites that will use other insects, often including crop pests, as hosts on which their larvae feed and eventually kill. Typically, all of this eating occurs during the larval stages, but some will still hunt as adults, supplemented with nectar and pollen.

By naturally regulating pest populations, beneficial insects can help minimize reliance on pesticides that have harmful effects on pollinators and soil health. 
 

Meet some of our favorite beneficial insects

1. Lady Beetles

With approximately 475 species in North America, lady beetles, also known as ladybugs, are highly regarded as voracious predators of agricultural pests. Most lady beetles are specialist predators of aphids or scale insects, though some consume whiteflies, mites, thrips, and insect eggs in the absence of their prey. This can sometimes include the eggs of the Colorado potato beetle (Leptinotarsa decemlineata), a common pest to gardeners and farmers alike. A single lady beetle may consume up to 5,000 aphids in its lifetime!

Fun fact: The name “lady beetle” originated in Europe during the Middle Ages - farmers named them “beetle of Our Lady” in gratitude for saving their crops.

Some lady beetle species have been distributed en masse to be used in biological control programs, such as in commercial greenhouses. This practice raises several ecological concerns among conservationists and researchers, so we do not recommend buying or releasing lady beetles. Instead, support the species already living in your area!
 

A photo of a lady beetle larvae eating an aphid on a plant stem.
While lady beetles are most recognizable as adults, where they sport their red (or yellow), black, and white coloration, their spiky larvae are also great predators of aphids and other pests!  (Photo: David Cappaert CC-BY-NC 3.0).

 

2. Assassin Bugs

There are approximately 160 species of assassin bugs in North America. These insatiable and aggressive predators are excellent at reducing pest populations and will often kill more prey than they strictly need for food. They use their powerful piercing mouthparts to ambush and feed on a wide variety of insect pests, including caterpillars, aphids, leafhoppers, grasshoppers, beetles, wasps, bees, and flies.

While they may occasionally feed on other beneficial insects, their overall impact on pest populations makes them a valuable ally in sustainable farming!

Fun fact: While waiting on a flower for prey to wander by, some assassin bugs will sip on nectar as a snack!
 

A photo of a large grey wheel bug, named after the cog or wheel-shaped hump on its back, sitting on a leaf and feeding on a beetle, looking as if it was drinking through a long curved straw.
Wheel bugs, named for the cartwheel- or cog-like shape on the back of their thorax, (Arilus cristatus) are especially valuable predators of caterpillars and Japanese beetles (Popillia japonica), an invasive species. (Photo: Lisa Brown CC-BY).

 

3. Flower Flies

There are approximately 900 species of flower flies in North America,  also known as hoverflies or syrphid flies. As larvae, many species are ravenous predators of soft-bodied insects such as aphids, scales, mites, and thrips. A single flower fly larvae can consume as many as 50 aphids per day! In their adult stage, flower flies are important pollinators, frequently visiting a wide variety of flowers to feed on nectar and pollen.

Fun Fact: Flower flies can beat their wings several hundred times per second, allowing them to hover in the air (hence their name “hover fly”). 
 

A photo of a flower fly, looking quite like a bee itself, pollinating a Black-Eyed Susan flower.
That’s no bee! Flower flies (in)famous for being mistaken as bees, often appearing mislabeled in magazines and newspapers, or, more humorously, field guides. Unlike bees, flower flies only have one pair of wings, and their eyes are also a different shape and size. (Photo: Raven Larcom / Xerces Society).

 

4. Parasitoid Wasps

With approximately 7,600 species in North America, adult female parasitoid wasps control pests by laying their eggs on or in the prey insect. Their targets can be eggs, nymphs, larvae, or adults, and include many different potential pests, such as caterpillars, grasshoppers, aphids, sawflies, mealybugs, scales, whiteflies, beetles and more. The larvae then develop on or inside their host, feeding on it but usually not killing it until they reach maturity and pupate.  

Many of these wasps are host-specific, which means they will only lay their eggs in specific host species. The life cycle of parasitoid wasps is very closely synchronized to that of their hosts, making them particularly effective in reducing pest populations.

Fun fact: The life history of parasitoid wasps in the family Ichneumonidae influenced some evolutionary theories of Charles Darwin.
 

A braconid wasp perched atop a caterpillar, while inserting its ovipositor into its prey.
Parasitoid wasps can be very tiny, but their impact on pests can be quite big. (Photo: Scott Bauer / USDA-ARS)

 

5. Tachinid Flies

With approximately 1,000 species in North America, tachinid flies look like a typical fly, but beefier and distinctly bristly. These parasitoids will lay their eggs on or within the larva of butterflies, moths, beetles, sawflies, true bugs, and grasshoppers, including many species that can be garden pests. Some tachinid flies will lay live larvae (instead of eggs) directly into their host.

Adult tachinid flies will often feed on nectar from flowers, playing an important role in pollination, and consume tree sap or honeydew excreted by aphids and scale insects.

Fun fact: Tachinid flies are known for their erratic zig-zag flight patterns! 
 

 A photo of a tachinid fly perching on a white flower. The fly has a grey head and thorax, and a bright red body, all covered in distinct black bristle hairs.
Take a closer look at the flies in your garden; amongst the fruit flies and house flies, you might spot a tachinid fly doing its best to control pest populations! (Photo: Whitney Cranshaw CC-BY 3.0)

 

Learn more about supporting beneficial insects: 

Authors

Raven Larcom

As the pollinator program specialist and administrator, Raven promotes the conservation of pollinators through direct technical support, outreach, and events in the Mid-Atlantic region. She also supports the pollinator team through program tracking, reporting, publication preparation, communications, event coordination, responding to public inquiries, and more.

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