Beneficial Insects and Spiders

Beneficial Insects and Spiders

Beneficial insects are those that feed on garden pests. They are important to all gardens as they require minimum effort to attract, they maintain a balanced garden ecosystem and keep pace with pest populations. Having beneficial insects in your garden makes it less likely that you will have a pest outbreak.

The first rule in attracting beneficial insects is to not use pesticides that leave toxic residue.  According to Penn State University, “many beneficials are more sensitive to insecticides than the pests you are trying to control.”  When you use dangerous chemicals in your garden you could be killing friendly bugs as well as pests.  If ever there is an outbreak of pests I use a soapy water spray to kill them. But try very hard to prevent pest problems on the outset and always try to attract beneficial insects to my garden.

A few quick words on prevention: build healthy soil with organic matter, use disease resistant plant varieties and put the right plant in the right place. Healthy plants are more resistant to pest problems.  They are able to fend off attacks and resist the spread of diseases brought on by pests. While we want to work to prevent pest problems, it is easy to get nature on our side.  By planting flowering species that provide nectar and pollen, you can attract beneficial insects to your yard.  Read a bit about that here (scroll down to "Beneficial Attractors") and more information will be posted soon.  In the meanwhile, read below to learn more about the beneficial insects that work in our gardens. 

Different Beneficials

There are two main groups of beneficial insects: predators and parasitoids. Predators eat multiple prey in their lifetime, are usually larger than their prey and kill their prey. Parasitoids are insects that have a free living adult stage that lays eggs on or inside a host and the young go on to parasitize (live off of) and eventually kill the host. Parasitoids are usually smaller they their prey and have one host over their lifetime.

Most of the common beneficial insects that I am going to write about are predators, a few are parasitoids. 

1. Spiders

Spiders are quintessential garden predators and very beneficial.  They control pest populations in the air and on the ground including flies, mosquitoes, moths, wasps and even slugs!

2. Green lacewing

Green lacewing larvae eat aphids and other soft bodied insects including mites, thrips, mealybugs, small caterpillars, immature white flies and some insect eggs. Can consume up to 200 prey a week. 

3. Ladybird beetle

Ladybird beetle or ladybug adults feed on nectar, pollen, and honeydew. Both adults and larvae feed on aphids, spider mites, scale insects, whiteflies, and small caterpillars. The larva (shown in the lower left picture) looks a bit like an alligator! They are black and red and very small, so keep a look out for these critters and cheer them on when you find them! 

4. Hover flies

Hover flies, also called syrphid flies, look like bees. They are important pollinators and their larvae feed on aphids in large numbers.

5. Predatory wasps

Predatory wasp adults feed on nectar as well as large pests such as caterpillars, beetles, and flies.

6. Minute pirate bug

Minute pirate bugs are very tiny (less than 1/5 of an inch long), very fast, and use their mouthpiece to such liquids out of prey such as aphids, thrips, and spider mites.

7. Assassin bug

Assassin bugs are predators that kill prey with their piercing-sucking beaks. Prey include aphids, medium sized caterpillars, leaf hoppers, asparagus beetle eggs and larvae, and small flying insects.

8. Big eyed bugs

Big eyed bugs have large round eyes for spotting prey. They feed on flea beetles, mites, insect eggs, and small caterpillars.

9. Parasitic wasps

Parasitic wasps are small non-stinging wasps. They are parasitoids, whose larvae kill their hosts, consuming over 200 prey species including aphids, bagworms, cucumber beetles, gypsy moths, cabbage worms, Japanese beetles, leaf-miners, squash vine borers and tent caterpillars. The photo shows braconid wasp eggs and larvae feeding on a tomato horn worm.

10. Tachinid flies

Tachinid flies are parasitoids of gypsy moths, cabbage loopers, Japanese beetles, army worms, cutworms, sawflies, codling moth, squash bugs and tent caterpillars.

Observe and Identify

As  you see from just this small sampling of the beneficial insects and spiders that exist in our gardens, there are many and it is difficult to know all of the ways in which they are helping your plants grow.  So be sure to watch the insects in your garden carefully, you never know if what you think is a pest is actually a helper!  Take the time to observe the new critter.  What is it doing? Does it seem to be chomping on your plants or is it consuming a caterpillar? Watch carefully and try to identify the beast using descriptions of its color and shape.  There are many good books that will help you to learn more about the insects that make up our garden ecosystem.  "Insects and Gardens: In Pursuit of a Garden Ecology" by Eric Grissell and "Garden Insects of North America" by Whitney Cranshaw are two of my favorites.