One Fly Gardeners Should Learn to Appreciate

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A typical hoverfly. Photo: http://www.kiwicare.co.nz

Humans tend to revile flies as annoying, disgusting, disease-carrying, biting pests and indeed, some of them are just that, but if you garden, there is at least one type of fly you need to learn to appreciate: the hoverfly.

There are thousands of species of hoverflies, also called syrphid flies, flower flies and drone flies, all in the insect family Syrphidae. They do what their common name suggests: they hover. While the head of the insect remains absolutely still, the transparent wings beat like mad, allowing the insect to hang in the air: a true little insect helicopter! 

Many (but not all) have bodies that are striped yellow and black or brown and gardeners often mistake them for small bees or wasps, but this is mimicry: they’ve adopted beelike colors to confuse their enemies. Hoverflies never bite or sting.

Hoverfly eyes (left) are huge and cover much of the head, bee eyes (right) are smaller and on the side of the head. Photos: Ted Roger Carston, USGS Bee Inventory and Monitoring Laboratory

If you look closely, though, you’ll see they have “fly eyes”: huge eyes like those of houseflies that nearly cover their head and often quite unlike the eyes of the bees and wasps they imitate: the latter have eyes that are well separated and are borne on the sides of their head.

There are different hoverflies found all over the world except deserts, extremely high latitudes and altitudes, and Antarctica. There are over 800 species in North America alone and as many, if not more, in Europe. Some tropical countries host over 1000 species! Dozens of different species visit most gardens.

Why They’re Our Friends

Adult hoverflies are pollinators, flitting from flower to flower, feeding on nectar and pollen. To compensate for this theft, they carry pollen and thus help pollinate plants. They’re believed to carry less pollen per trip than bees, but then, they make more flower visits, so are often just as efficient. 

Hoverflies tend to prefer open flowers. Photo: Alvesgaspar, Wikimedia Commons

Their short mouth parts make them poor pollinators of tubular flowers: they prefer open flowers and are fond of plants in the Asteraceae (sunflower family), Rosaceae (rose family) and, especially, Apiaceae (carrot family). They’ll pollinate flowers of any color, but are especially attracted to yellow and white flowers. Scented flowers also attract them. Most hoverflies are generalists and will visit a wide range of flowers, but some are specialist pollinators. Cheilosia albitarsis, for example, only visits buttercups (Ranunculus repens).

Hoverfly larva feeding on aphids. Photo: Beatriz Moisset, Wikimedia Commons

So much for the adults, but many of the larvae are also useful. Now, there are species whose larvae are detritivores (eating decaying plant or animal matter) and others are aquatic, but many are insectivores: they feed on harmful insects, including leafhoppers, thrips and, especially, aphids. Indeed, some hoverfly species are being studied for use as a biological control of plant pests. Typically, female hoverflies lay their eggs near a colony of their favorite pest insect and when their often slug-like larvae hatch a few days later, they begin chowing down.

Hoverfly larvae retreat into a cocoon at the end of their feeding frenzy, then hatch into adult flies 10 or so days later. There are several to many generations per summer, depending in the species and the local climate.

Attracting Hoverflies

Hoverfly on an umbellifer. Photo: David Short, Wikimedia Commons

Hoverflies will visit most gardens on their own if there are plenty of flowers and you don’t spray with insecticides, but some flowers attract them more than others. Often gardeners plant species such as bachelor’s buttons, buckwheat, chamomile, coriander, garlic chives, marigold, oregano, phacelia, sweet alyssum, tansy and yarrow as companion plants in or near vegetable beds to ensure the presence of hoverflies and other pollinators.


Hoverflies: the best gardening friend you never knew you had!

Friend or Foe? A Closer Look at Insects

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boy looking in magnifying glassI’m always surprised that many otherwise very experienced gardeners know very little about the insects that frequent our gardens. How many times have I received an email from a gardener looking for a powerful insecticide to eliminate an insect that turns out to be harmless or even beneficial? While I can’t possibly incorporate into a single blog all the good and bad bugs (there are thousands!), I thought I might at least try to point out a few common cases of mistaken insect identity.

Ladybugs and Lily Beetles

You’re be surprised how many gardeners confuse the ladybugs (also called ladybirds) and lily beetles. Yet they are very different.

Ladybugs are small with a rounded, dome-shaped body. There are dozens of species, but usually they have contrasting spots (black dots on an orange, red or yellow background or yellow or orange dots on a black abdomen, etc.), although a few bear no spots whatsover. They have a black head with clearly visible white spots. Ladybugs are very effective predators that eat aphids and other small insects that harm plants. Therefore you don’t want to poison ladybugs with insecticides!

The scarlet lily beetle (Lilioceris lilii), on the other hand, is larger than a ladybug and has a brilliant scarlet coloration with no spots. It has an elongated body, not dome-shaped. It consumes the leaves and flowers of lilies (Lilium spp.) and fritillarias (Fritillaria spp.). A good way to distinguish between a ladybug and a lily beetle is therefore to determine what plant it is found on. If the plant is not a lily or a fritillary, it’s probably not a lily beetle.

There are several ways of controlling lily beetles (hand picking, spraying with neem oil, etc.), but none are 100% effective. The easiest way to deal with them is to stop growing lilies and fritillarias.

Ladybugs and Potato Beetles

People often confuse Colorado potato beetles (Leptinotarsa decemlineata, also called potato beetle or potato bug,) with ladybugs, but the two are easy to tell apart. True enough, both have a similar dome-shaped body, but ladybugs usually have spots on their back, while potato beetles are not spotted, but striped black and yellow. Also, they are much bigger than ladybugs. Again, knowing what plant you find them on will help identify the insect: ladybugs can be found on almost any plant, but potato beetles will only be found on potato plants or, more rarely, other plants in the Solanaceae family (tomatoes, eggplant, etc.).

Controlling the Colorado potato beetle control is not easy, but you can reduce its impact by practicing crop rotation and interplanting the potato plants among other plants. Or you can cover your potato plants with a floating row cover. If you choose to use insecticides, prefer a product that is not toxic to humans.

Bees and Wasps

Lots of confusion here! The problem is that there are all sorts of flying insects with a black body bearing bright yellow stripes. All are generally beneficial to some degree (bees and hoverflies are good pollinators, wasps are predators that consume other insects), but bees rarely sting unless you provoke them. There is therefore every reason to want to encourage their presence in your garden.

If ever a bee stings you (which is rare), it will pay the price because it leaves its stinger embedded in your skin, leaving a gaping wound on its abdomen that will eventually kill it. That also means it can only sting once.

Bees are distinguished from wasps by their much stockier body, usually with visible hair on both the abdomen and legs. Their behavior is also different: they pretty much ignore people and concentrate all their efforts on visiting flowers where they play a vital role as pollinators. They often make buzzing a noise when they fly. There are many species of bees of all sizes. The best known is the honeybee (Apis mellifera) which produces the honey we eat.

Wasps are more closely related to ants than to bees. They belong to many different genera and there are literally hundreds of thousands of species. They are more slender than bees, with a narrow waist (which is where the saying “wasp waist” originates). They appear hairless and they make no sound when they fly. Unlike bees, they don’t die after stinging and can sting several times.

Most wasps are solitary, with each female living independently. Solitary wasps are not aggressive towards humans and in fact, pay little attention to them. Many, indeed, are so small they are essentially invisible. Although some may sting if provoked, many won’t. In general, the least aggressive species are black or, at least, don’t have bodies strongly striped yellow and back. (In nature, yellow and black stripes serve as a warning to other animals that their bearer stings and is not to be disturbed!)

It is the social wasps, notably those of the Vespidae family, that are to be feared. They are fairly good-sized insects (hornets, one type of social wasp, are the largest) and most species bear the typical black and yellow (or black and white) warning stripes described above. Being omnivores and not just pollinators, they find human foods attractive, especially sugary ones, and often investigate our meals when we eat outdoors.

Unfortunately, social wasps do tend to be aggressive. They will sting if you approach their nest and may also sting when you wave your hands to try and chase them off your meal or away from your face. It’s best to act cautiously when they are around: sometimes backing off is the best thing to do.

Social wasps live, as the name suggests, in colonies, with one queen and numerous workers. Some species live hidden inside structures (house walls, tree trunks, wood piles, etc.) or underground, while others build more visible nests of paper or mud. If you discover a nest in a place where there is a risk that humans could be attacked, mark the area with brightly colored tape to alert passersby. Then at night, when they are asleep, you could use a commercial wasp-control product to kill the colony. If the nest is inaccessible, it may be worthwhile bringing an exterminator.

Honeybees and Bumblebees

There are also thousands of species of bees, among which the honeybee is best known, but bumblebees are also frequently seen in our gardens. Contrary to popular belief, the bumblebee is not the male of the honeybee, nor is it a queen bee, but belongs to another genus entirely (Bombus instead of Aphis). Bumblebees are bigger, fatter and much hairier than honeybees. They are even less aggressive than honeybees and the risk of being stung by a bumblebee is minimal.

Bees and Hoverflies

Hoverflies are beneficial insects that fly from flower to flower like bees, often hovering over them before landing, whence their name. They are often (but not always) striped black and yellow, like a bee or wasp, and are therefore often mistaken for one or the other, but this is a case of mimicry. Looking like bees helps discourage their predators. However, they are neither bees nor wasps but a type of fly called a syrphid. They neither sting nor bite and are harmless to humans.

Adult hoverflies are important pollinators while the larvae of many species are predators on other insects, notably aphids. Thus they are doubly useful to gardeners. Others eat decaying plant and animal matter, also good news for gardeners. Once you study them a bit, you’ll find they are easily distinguished from bees or wasps by their huge eyes that seem to cover most of their head!

There you go! A portrait of a few common insects that we sometimes misidentify. Learn to recognize and respect them and it will make your gardening experience much more satisfying!