How to Scout for Bugs: The Good, The Bad and The Ugly.

By David D. Spencer

Vice-President, Applied BioNomics

The essence of scouting:

On an early sunny morning this June, I will walk out to my garden – coffee in hand – and bask in the glory of the garden I have facilitated. But, after a brief moment of contentment, I will – as history proves – see something that needs immediate attention. It may be a wilted plant, a seedling that has disappeared or a dog-dug hole in an otherwise perfect bed. Within moments I will be deep into the garden rectifying problems, looking at soil, turning over leaves – basically, just gathering information; It is a daily observation of my garden. A little while later, when my wife is wondering where I am and my neighbour is wondering if I’m crazy, I will scout for where I placed my now luke-warm coffee and get on with my day. This habit (of observation – not misplacing coffee) is the essence of scouting. With a little information, this habit can become an essential tool in the health of your garden.

Why scout?:

In an outdoor setting, if one has not applied pesticides, fungicides, soaps or other home-remedies, there is no end to the quantity and variation of micro flora and fauna in the garden. With this complexity and abundance there are very few pests that will become plentiful enough to outright kill your plant. However, when we garden for aesthetics in a flower garden, or for yield in a vegetable garden or road-side stand, small numbers of pests can have a significant impact. Scouting will allow you to learn what’s in your garden and when to (if necessary) panic. However, scouting is not just used to identify pests. Indeed, finding a small colony of aphids is sometimes also the same moment you find that some are already being parasitized by native aphidius wasps. Instead, scouting is keeping records and gathering information on all the insects, good, bad or ugly so that, should you need to act, the right intervention is done at the right time in the right way. This has the ability to save you time, money, and your plants.

The Good:

Everyone recognizes the ladybug. In the presence of aphids seeing a lady bug might mean that no action is required on your part. But, to be sure, one must also identify ladybug larva and eggs. Ladybugs are generalists and are not as likely to clean up your aphid problem as some other players. But should you find several clusters of eggs, then you will more likely have control. Another aphid predator, the wasp aphidius is most often identified by the aphid-mummy it produces as it parasitizes aphids. The presence of aphidius aphid-mummies usually indicates that the current aphid population will soon be reduced. Like the ladybug and others, it is as important to know the good bugs as it is to know their differing life-stages. As a general rule, expect all wasps to be good for your garden. Likewise, hoverflies, and round-bodied beetles and any mites you see moving quickly can generally be assumed beneficial. True bugs are more difficult as they are generally split between pest and predator. Regardless of the insect or mite, one should consider buying additional predators or planting predator friendly flowers as needed. Allowing cilantro and plants from the onion family to flower and planting borders of alyssum are my favourite ways to both promote beneficial insects and to observe them.

The Bad:

You likely know these. As with the good bugs, knowing their lifecycles and stages is advantageous. Aphids have both a sexual winged stage and an asexual stage where clones of themselves are live-birthed. Seeing winged aphids in our local area usually means an explosion of aphids is imminent. Seeing a group of large aphids surrounded by tiny ones is a sign you can have thousands of aphids on one plant in a matter of days. One of the reasons people seem to observe aphids “coming out of nowhere” is because of this ability for a population explosion, but another reason is some aphids have host plants that are separate from the ones they most commonly infest. For example, those black aphids on your nasturtiums: they are black-cherry-aphids and they need prunus trees (plum family) to overwinter. Treating plums and cherries early in the year with aphidoletes  – the aphid predatory midge – is often a sure and effective way of promoting a better balance of pest and predator.

Whiteflies, that we encounter usually late in the summer, are another interesting pest. The whitefly do not often kill the plants, but the thousands of eggs they lay on undersides of leaves can lead to the plant’s death. Each scale produces honeydew by drawing sap from the plant, stressing it and allowing molds to establish on the sticky honeydew. Scouting for whitefly is sometimes as easy as taping a leaf to see if adults fly around, or as complicated as looking for slightly shiny, sticky leaves.

Spidermite is most often identified too late: once webbing is established. But regular scouting of your plants will find spider mite damage on the leaves much earlier and more easily than looking for the actual pest. Look for mottled spots on soft leaves, as individual cells are damaged and appear bleached.

Thrips: Use trap plants and buy and apply amblyseius Cucumeris regularly. Thrips damage often appears weeks after it has started. The curled cucumbers, deformed flowers, sparse mottling of leaves are signs that thrips have been present and damaging for weeks. Checking traps plants regularly allows you to know when to bombard any precious plants with your beneficial insects. Thrips love yellow pom-pom marigolds. Plant these to use for scouting, to attract thrips from more valuable plants and to use as a sight for establishing Cucumeris.

The Ugly:

Sometimes our worst pests are the biggest – the caterpillars. Some people go great lengths to destroy caterpillars, when often the solutions are relatively simple. Unfortunately, some of the predators of caterpillars are ugly: Spiders, yellow jackets, birds (not so ugly), earwigs and fungi/bacteria. While I will never suggest keeping and maintaining wasp nests to help control caterpillars, I will suggest to stop applying chemicals – even if it’s dish soap or vinegar, and stop trying to trap these potential predators, unless they become the pest.

Another ugly player is the Black Vine Root Weevil. Black vine root weevil often presents itself as notching on the leaves of rhododendrons and azaleas. But, they are tricky to scout-for since the female (that does the notching) can travel several kilometres every night to feed. Instead, brushing aside the top layer of soil around those plants may expose their larva. However, it is still not usually so easy. Black vine root weevils often prefer black berry thickets, cedars, and spruce, so scouting could take place in these locations. But, since crawling into the blackberries or checking every tree will ensure your neighbours think you’re crazy, it is best to assume they are there or just check one or two spots. However, I suggest you immediately apply stratiolaelaps scimitus (a predatory mite) to your soil anyways. In some areas Black Vine Root Weevil only has one lifecycle per year and they are most susceptible in the few days immediately after the eggs have hatched. Stratiolaelaps is a predator of many pests in the soil and will result in diminishing Black Vine Root Weevils years after year. Now your neighbour may thank you.

How to scout:

You likely already have the fundamentals of scouting: observing, turning over leaves, turning up a bit of soil..etc. Knowing a bit about the nature of certain insects will allow you to take a few extra steps to find some of the well-hidden insects and mites. For example, around noon on a hot day humidity will be at its lowest, expect most invertebrates to have made their way to cooler more hidden areas than where you’re likely to see them. So concentrate scouting in the morning or late afternoon. Mealybugs need protection from some of the larger predators so they are most often found down in the crowns of plants. It is always worth gently pulling leaves and stems aside to search these areas. Of the brassica family, expect to see aphids in folds and tight spaces. Tap flowers onto your hand or white paper to look for thrips. Look under leaves for soft-bodied pests of those in their soft larval stages. New tender growth often has the most attention from pests, however it is often prudent to look under older leaves to find insects with slower lifecycles like the scale of whitefly, frass from lace bug or other scale. As you can see, there is no shortage of places to look. The important thing is to see them early, look for predators and decide if nature will take care of this problem for you.

Use your garden:

What plants suffered from pests last year? Do you remember or did your record when those pests arrived? I often suggest two methods for using your garden to make scouting more efficient. First, if you have a beloved plant that often receives unwanted attention from a pest, use that to know when the pest arrives in the garden. For example, if your rose gets bombarded with thrips damage in the first week of June, then expect thrips to be everywhere in your garden that same week. Do your cabbages explode with grey cabbage aphids early in April? Knowing which plants are the “canaries in a coal mine” of your garden will allow you to focus attention on them, rather than scouting your whole garden. Similarly, my second strategy is to provide the “canaries.” I always recommend planting a sacrificial bean plant (primarily the variety “strike”) near any plants you expect to get spider mite pressure. Strike is a preferred plant for spider mite and its leaves show spider mite damage within hours. This allows you to get a head start on finding spider mite damage. One of the bonuses of these strategies is that if you are using beneficial insects in your garden, these “trap plants” are the perfect location to not only apply the beneficials, but also to allow their populations to increase and spread throughout your garden. If you are wondering what other trap plants are available, consider all the plants you have grown that suffer the most or the quickest – perhaps they are plants you have sworn to never grow again. Eg. Cabbages and nasturtiums for aphids; yellow pom-pom marigolds for thrips (tap the flower head against your other hand to see if thrips fall out).

Where to scout:

As mentioned, trap plants or plants that regularly suffer from pests are a great start to your observations. Additionally, all plants that are experiencing stress are plants you must scout. Stressed plants are more favourable to pests. They can detect the stress via smell (some plants produce alcohols or other compounds when stressed), sight (stressed plants reflect different wave-lengths which can be visible to insects), or the presence of other insects (honeydew producing insects can attract other pests). So, if your a plant wilted the day before; you over-fertilized and produced too much soft new growth; a new plant was planted in the wrong spot; or soil is overly-wet, then be sure to get on your hands and knees, turn some soil over, look on top of and underneath some leaves and continue to monitor until the stress is alleviated.

Record keeping:

Most gardeners keep records for seeding, transplanting and harvesting. I suggest adding your scouting notes to these records. Try to include by week:

Scouting log.



Action taken

Other pests/predators


Week 15


Cabbage aphid



Two areas about 3” diameter on one plant.

Week 16


cabbage aphid



Many aphids have been parasitized and are mummified.

Week 16

Yellow rose on eastern fence

Green aphid

Hosed off with plain water


Found just on the buds.

Week 17


cabbage aphid



Aphids are gone.

Week 17

Yellow rose on eastern fence

Green aphid



Water knocked numbers down. I’ll wait and see what predators establish.


Just a little information about insects or mites and their life-cycles allows you to integrate pest and predator scouting into your regular garden observations. Record keeping is a fantastic opportunity to prepare a garden for success, so is the application of some preventative beneficial mites or insects. But the most satisfying part of scouting in a healthy backyard garden is when you become comfortable identifying pest and predator, you recognize that the presence of many pests do not require any intervention on your part. Nature might appear to be slower-to-react than the squeeze of a spray nozzle, but it is always hard-at-work. Achieving the natural balance is your primary goal. And then, should you need it, applying beneficial insects might be useful when you need to slightly tilt that balance in your favour.

Additional Information:

Please check-out our website: for more information. You will find discussions on pests and predators and crop specific technical advice. Look under “landscape” for home garden relevant information. There is also an “ask the doctor” section should you have any questions specific to our products.

The Author:

David Spencer has been the Vice-President of Applied BioNomics ltd for one year, but has been with the company as Technical Director, System Manager, and other roles for over 20 years. David returned to North Saanich for the space to garden and raise a family after a 7 year period of career.


Lacewing lava eating aphids

Amblyseius cucumeris eating thrips

Scouting for root pests (close up of broccoli maggots)

Syrphid fly – Aphid predator

Aphids with aphid parasitoid aphidius