How to Attract Beneficial Insects to Your Garden: Lesson 2 – If you build it, will they come?

Lesson Two: If you build it, will they come?

This lesson will focus on structures that promote (or claim to promote) beneficial insects in your yard.

Some structures in the garden have been proven to aid organic gardens in a variety of ways. Most notable and obvious is keeping honeybees to promote pollination of fruit trees. But remember: Honeybees are not endangered, contrary to popular belief. Honeybees are not native to North America. They are an introduced species from Europe. (A study published January 2021 from the East Coast proved the negative impact honeybees have on natural bee populations: reference to the publication is here .)

Onions left to flower are favoured by honeybees

Essentially, they are considered livestock and can potentially spread harmful diseases and parasites to native pollinators. However, it’s an enjoyable hobby, and highly productive. I don’t discourage bee keeping, but I encourage people to stop associating it with anything positive for the environment. So, while honeybee hives are a good example of a structure designed and built by us to facilitate their livelihoods, that is all I will say about honeybees.

Harvesting my roof top bee hive in Vancouver BC (2018)

Mason bees. Considerably less disruptive to the environment than honeybees, but still not ideal. Creating any space for a high density of insects (like mason bee houses or hotels) will invite predators and parasites, diseases and viruses.  Stratiolaelaps scimitus has a 100% success rate (in hundreds of replications) of killing varroa mites in a controlled environment. Many bee keepers are applying it to honeybee hives and mason bee structures (prior to winter cocoon) in hopes that the stratiolaelaps mite will eat the varroa mites before they are sealed inside honeycomb or cocoon. It’s worth a try if you plan on keeping bees. But, if you build these mason bee structures, they will come (Or you may have to buy them), so it’s a nice addition to your garden. Also, like honeybees they are not easily deterred by your presence, so they are easy to watch.

One of my “Bee Houses”

Native bees: Bumble Bees: In their natural habitat bumble bees require bare ground to construct their hives. So don’t be so quick to mulch every square inch of space. In my area, borage and California poppies (both sort-of weeds here) are favourites of our native bumble bees.

Bumble bee on california poppy (with other weeds)

I find buckwheat particularly helpful in attracting other bee species like sweet bees. But other bee structures can be utilized. Take a block of wood and drill various size holes directly into the blocks. Ideally you will have depths of several inches and diameters of varying sizes. There is one catch. Some bees, like carpenter bees will use these spaces to carve out one more suitable by chewing on splinters and widening the opening. However, other bees use the holes formerly polished by carpenter bees. To directly promote them, care should be taken with sand paper to smooth the openings so there are no rough spots. While this promotion is simple, and a nice addition to the garden, the best thing you can do is leave dead trees standing. A decaying standing tree is home to all sorts of these bees and other species. Have an arborist come and assess a dead tree. Typically most of it needs to be removed in order to make the remaining truck stable enough to leave safely.

A “bee post” at a large nursery in Oregon.

Butterfly / Ladybugs Structures: Simply a gimmick – but look cute and something will end up living there, but not likely what you intended. Butterflies simply don’t need structures and ladybugs might pupate in a house, but they might also pupate on the fence next to that house. The invasive ladybug Harmonia arydaxis often ends up in large numbers and pupate together. You might be lucky and select where this happens, but it appears to be at random. Don’t use these gimmick houses unless you just think they look cute in your yard. (I have my kids paint all sorts of useful garden decorations!)

Bat/bird houses: These are predators of beneficial insects, but essential in keeping balance. If properly installed, they will be inhabited and will liven-up your yard and cut down on certain pests. It might seem counter-intuitive to invite the predators of beneficial insects, but don’t worry. They eat the bad ones too (and particularly, mosquitoes).

Pond/Water feature: I consider this essential. We have long dry summers where I live. Many predators require water to drink, but plant pests typically do not. For example, aphids get both the food and moisture they need from sucking on your plants. Predators that eat aphids for food may require water for fluids. In most cases, dew or rain trapped in leaf-folds are enough, but during dry periods you will see them all buzzing around your water feature. So water features disproportionately promote beneficial insects.

A variety of plants is required for a variety of bugs.

The most common counter argument to installing a water feature is that they attract mosquitoes. But, if you have a deep or cool-enough pond, you will get mosquitos and also their predators (beetles, dragon fly larva..etc). Consider this: after a rain, mosquitoes will lay eggs in any standing water. Typically that water warms up and evaporates so you get all the mosquitoes (which are quick to emerge) and none of the predators. So establishing a cool, permanent water feature promotes the predators of mosquitoes, keeping their numbers in check. And if you’re really concerned about mosquitoes, don’t forget the bat house. Each bat can eat 10,000 mosquitoes a night! Some common mosquito predators that depend on stable, cool water features are dragonfly larva, and water beetles. Both welcome additions to the garden. Besides, water features are just nice to have. I can get lost sitting and watching all the living things surrounding a water feature midday in a hot summer. Bonus: Add some gold fish if you want to attract Herons or other birds of prey!

My daughter “mucking” in the pond (as I like to call it.)

Wood and rock piles: I don’t like spiders. But I do have a wood stove and a stack of fire wood. I keep it away from my house because I see all sorts of bugs in there that I don’t want indoors. But that just shows how important they are. A wood pile mimics a large fallen tree or pile of branches. It supports the bugs that break down wood, as well as their predators. It’s another piece of the puzzle. I don’t recommend building a wood pile for promoting insects, but you can build “bug hotels” which are often smaller, more controlled-looking, structures of bark and small dimension wood. Important features are: spaces protected from rain, different woods, bark and pieces at different states of decay. If you have kids send them on a scavenger hunt (with gloves) to bring back and create a bug hotel.

Rock Piles simply don’t sustain the same amount of life, however they can create spaces protected from rain, and they are important spaces for cold-blooded creatures that need to warm-up: like snakes (another essential animal for controlling bug populations). But, most importantly, many predatory mites do the same thing! (Warm up on exposed rocks). So line a bed with rocks a few rocks deep and wide or build a gabion rock structure! (One of my projects for this spring.)

A bug hotel at the University of Quebec at Montreal

From my garden: I have 20 raised beds and some side gardens all built with spruce. It is a poor wood to use, because it breaks down easy: however, that is exactly why I used it. I may try something more permanent in the future, but in the meantime, as that wood rots (before it looses structural integrity) it becomes home for a variety of bugs and can help retain water. While I wouldn’t say the raised beds are structures that promote insects, the alternative building materials (cedar, concrete, metal) offer almost nothing in terms of habitat. Also, ten of those beds have 8 foot posts.

As you’ll see from the picture above, many of those posts have bird houses. Also on each one is some sort of “bug house” or “bee block”. I love these posts. I use them for structures to support plant grown as well, but they give an element of height in the yard even during the “off season.” Plus high points, like bamboo stakes, my posts, or single tall plants serve as perch points for many predators like hunter flies and dragonflies. So, give your garden some height!

There are lots of options to build structures that promote life in your garden. I like to think of my role in the yard as a “facilitator of life.” Never spraying anything (even soaps and oils) and creating habitat is the only way to a healthy yard. And remember, you will always get pests, but pests are food for predators. So the absolute best thing you can do to promote beneficial insects is to offer them food by leaving those pests alone. Consider this: If you actually try to produce aphids (like I have to do for work) you will fail. Try it! Grow some sacrificial plants for aphids. Over-fertilize them to make them attractive to pests and see how long you can keep aphids on it. My bet: less than three weeks.

So there you have it. Lots to do. Get building!

Lesson 3 – Lawn and the No-Till-Garden

Lesson 4 – Compost and Thresholds

Missed one? Lesson 1 – Should you plant flowers?

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