Are caterpillars eating the heck out of your garden every summer? Maybe you battle the tomato hornworm in summer or the cabbage worm in fall and winter. But did you know you can simply invite someone to come knock these annoying visitors out, and you don’t have to do much more than plant a few plants?
Enter parasitic wasps! These are some of the best insect allies to have on your side. They prey on various caterpillar species, leafhoppers, aphids, true bugs, and much more. Their main line of defense for you is their ability to lay their eggs in the bodies of these pests.
If you want to encourage them to come to your garden, there are ways to do that as well. Understanding their life cycle, the plants they like, and their food sources is great to know ahead of bringing them in. This ensures they’ll stay in your garden and continue to help you control pest populations.
What Are Parasitic Wasps?
Parasitoids like braconid wasps are Hymenopteran insects that lay eggs on or inside garden pests.
Parasitoids are members of the Hymenopteran superfamilies, the Chalcidoidea species, the Ichneumonidae species, and the Braconidae species. Gardeners most commonly come into contact with Braconidae, which houses the beloved braconid wasp.
What these three families have in common is their ability to oviposit (or lay eggs within or on) the bodies of common garden pests. When their eggs hatch, the larvae consume the host from the inside out as they mature.
A Wide Breadth of Species
Parasitoid wasps are tiny insect predators that play a vital role in controlling pests like aphids and caterpillars.
There are over 1 million species of parasitoids in the world. North America hosts about 740 of these. All of them are small, usually less than 1 millimeter long at full maturity. Unlike paper wasps, mud daubers, and other common wasps, parasitoids are not hive dwellers and, therefore, don’t sting.
You may not have even noticed their tiny bodies flying around your garden, working hard to keep various larval pests and aphids at bay. As we mentioned, the braconid wasp is probably the most important for food gardeners. Their main source of food is aphids.
If you see caterpillars in your garden with multiple lines of white masses on their backs, these are the eggs of parasitic wasps. The larvae may be within the bodies of the hosts or briefly on their backs before entering their interior. Aphid mummies are evidence of the presence of Braconidae. These look just like aphids but hollowed out, with a hole in one end.
All of these wasps rely on other insect species to continue their life cycle, whether it’s aphids, caterpillars, or another garden pest. Without their preferred host to lay eggs on, they cannot survive. But that’s good news to those of us who want the pest insects gone!
Life Cycle of Parasitoid Wasps
Parasitoid wasp life cycles vary in complexity and duration, but their life stages include egg, larva, pupa, and adult forms.
While it would be awesome to fully detail these wasps, each has a different length of various phases, with lots of variation and complexity between species. The life cycles of all, though, do have the following stages occurring in this order: egg, larva, pupa, and adult.
Some species need to mate to reproduce, and others don’t. Certain species’ eggs hatch only one larva, and some hatch multiple larvae. They may have multiple stages within the larval stage itself, or there may be just one. Finally, several species have multiple generations of offspring in a season, and others have a life cycle that lasts a year.
The larvae of these wasps develop inside the body of the chosen host, on the body surface, partially embedded in the body, or even externally, and leave when they’re mature enough. This may cause hosts to languish during feeding, or in the case of hornworms, the hosts lead normal lives until the nymphs emerge.
Some carry a virus that can alter the behavior of the host, which can prevent immune responses that eliminate eggs laid in the body. Other species are able to inject a virus that makes the host docile enough to be led to the hovel, where eggs are laid and the host is quartered off.
Primary Food Sources
Parasitoid wasps have diverse food sources, with adults consuming nectar and pollen and larvae feeding on various insects.
Because there are so many species of parasitoids, there are tons of food sources. Adults feed on the nectar and pollen of preferred plants. When it comes to larvae, all of them feed on other insects and arachnids. Let’s break these down into a concise list!
- Scale Insects
- True bugs (such as shield bugs)
Some species focus on one other species as their main food source. Others are what are called generalists, feeding on a wide array of insects. Some types have preferred plants to work around, while others are generalists in that spectrum as well. Knowing which plants they like is one way to bring them in!
How To Attract Parasitic Wasps to the Garden
Plantings are important, but there are other things to consider when it comes to bringing in parasites. You have lots of tools at your disposal here, and you’ll be most effective in hosting these tiny insects with a well-rounded approach.
Covering all your bases is incredibly important if you plan to spend money on a colony of parasitic wasps. Otherwise, you’ll release the colony, and they’ll relocate to a more hospitable territory.
Plant additional pest-prone plants to attract parasitic wasps, such as extra pepper or tomato plants for hornworms.
Outside of the specific plants that adult wasps feed on, plant more than you need of the plants the pests they prey on like. Add at least one more pepper plant or tomato plant that will attract hornworms, and the wasps will come to feed. The more hornworms you have, the more likely it is that your local wasp population will hang out.
Dense plantings are more attractive to insects in general. As you’re planting, pay attention to the space you provide for the plants. They need room to develop lots of fruit for you and plenty of foliage for the insects. Ensure they’re not so close, though, that diseases develop.
One great way to bring in all kinds of wildlife is to provide a water source, whether that be a small saucer with rocks or a full pond. Parasitic wasps are no exception to the benefits that water brings.
Plant companion plants like alyssum, cilantro, dill, yarrow, and carrot flowers, especially those with composite flowers and umbels.
There are so many plants you can plant with your veggies that these wasps like. Alyssum, cilantro, dill, yarrow, and carrot flowers are just a few. Most plants with composite flowers and umbels are attractive to them.
Like all insects, these guys have a color preference. Plant lots of blue, yellow, white, and purple-flowered plants. This is their preferred palette. All these plants work to bring in the wasps and also bolster the growth of your agricultural crops.
Avoid using insecticides and herbicides in garden areas where you want parasitic wasps to thrive.
Insecticides can negatively affect insects, especially when they’re applied incorrectly – organic and inorganic types included. Some herbicides have a negative effect as well. That’s why it’s best to avoid using them in garden areas where you want wasps to live.
If you must use insecticides or herbicides, use them properly. Consult the label, follow directions, and avoid applying sprays and dust in the middle of the day or as the sun rises. This is not only peak time for parasitic wasps but other pollinators, too.
Try to make insecticides a last resort, and have patience. As you bolster the habitat for these guys, you also bring in other pest controllers. Eventually, they’ll do all the pest control for you.
5 Plants That Attract Parasitic Wasps
Let’s talk about the plants you can include in your garden to lure in the wasps. The flowers of each of these plants have their small size in common. Larger flowers included here are actually composite in botanical structure and have clusters of nearly minuscule flowers.
Plant carrots, Queen Anne’s Lace, fennel, cilantro, or dill to attract parasitoids.
These are huge for bringing in small insects. If you’ve planted carrots in the fall and you’ve allowed them to overwinter in your garden, leave a few in spring. In summer, these will bloom beautiful flowers that parasitoids love, and you’ll get some seeds from their pollination.
Other plants in the carrot family work just as well if you’d prefer to plant them. Queen Anne’s Lace, fennel, cilantro, and dill are perfect attractors. Fennel and dill also happen to host swallowtail butterfly larvae, so everyone wins here!
Plant asters for their attractive, long-blooming flowers that attract beneficial insects.
Not only are asters long-blooming, they are simple to grow, and their disc-like flowers are just gorgeous. Their bluish and purple petals bring in your local parasitic wasps with ease. These are also great for bringing in ladybugs and their aphid-destroying larvae.
Those with gardening knowledge know the wide breadth of the aster family. Plant cosmos, yarrow, goldenrod, tansy, and coreopsis. Plant fall asters and watch them bloom from late summer through fall. Many of these plants are native to most of North America and are mostly perennial.
Enhance your garden with nitrogen-fixing flowering legumes like peas and beans to attract parasitic wasps.
Add a nitrogen fix to the soil with lovely legumes. There are plenty of peas and beans you can plant between other crops to ensure you get wasps frequenting the space and a huge harvest for your kitchen. A cover crop of vetch is a surefire way to bring the wasps in and condition soil for spring.
There’s an inordinate amount of native legumes that have vibrant, lovely flowers, too! If you prefer to plant native, look for partridge pea, clovers, lupines, and senna.
Allowing kale and other brassicas to flower can attract parasitic wasps.
While your kale plants alone won’t attract parasitic wasps with their leaves, they will if you allow them to flower. Many other brassicas are also perfectly good companions due to their ability to flower for long periods. Alyssum is one notable example that also attracts ladybugs.
Wild mustards bring in the wasps, too. It’s advised to keep these off to the side of the garden rather than in the growing space, as they can also bring in a few pests. However, that may be more fodder for the wasps!
Plants like lantana, mock vervain, and prairie verbena with continuous compound blooms are loved by parasitoid wasps.
Lantana, mock vervain, prairie verbena, and more are great for parasitoids. Wasps adore their continuous compound blooms and will return to them over and over. They also attract bees and butterflies, adding an extra layer of pollination to your veggie garden.
Parasitic wasps are not hard to bring into your yard, as many of the common veggie companions are those that attract them. Intercropping these and letting parts of the yard grow wild are easy ways to build a healthy and active predatory population.
Parasitic wasps and all beneficial insects also appreciate a water feature. This is easily attainable in both larger and smaller growing spaces. With a little bit of planning your garden, you can have all the pollination and pest control you need!