Know your hoverflies

Bees attract attention. Even if you’re not afraid of them, when there’s a bee around, you take notice. Besides the fact that they sting, bees have been in the news because of their decline due to the mysterious colony collapse disorder. But don’t be too quick to judge that yellow-striped insect pollinating your parsley. It might not be a bee at all, but an equally important hoverfly, like the one on my parsley, shown above.

Honey bees provide the essential hard labour pollinating many valuable food crops, especially the vast majority of fruits and nuts that we eat. So their decline has raised alarm in the food industry. Ironically, industrial agriculture might be partly to blame. Some research has shown bees exposed to neonicotinoid pesticides collect less pollen. Poorer foraging could threaten the survival of the colony.

Honey bees are a managed species like cattle or wheat. The most common and important species, Apis mellifera, is believed to have originated in Africa or Asia. It became the first domesticated insect. It spread with the help of humans, and they introduced it to North America, South America, Australia, New Zealand and East Asia within the past five hundred years.

Honey bees as pollinators contributed an estimated $2.03 billion in additional harvest to the Canadian farm economy in 2013, while honey and related products were valued at only $200 million.

How can hoverflies be that important? Maybe they are not, considering only their direct economic value. A 2011 study found that wild pollinators performed more than one third of the pollination of crops in California. Wild pollinators include wild bees, wasps, hoverflies, other flies, butterflies, moths, and beetles.

Hoverflies represent just one part of a diverse mosaic of species that pollinate our crops and native plants. An industry that relies so heavily on one species such as the honey bee is at risk. Biodiversity is essential to achieving food security. Small farmers have known this and diversified crops for centuries.

But hoverflies also do double duty as biocontrols. The larvae of some species are voracious predators on aphids and other soft-bodied prey. They are as effective as ladybug and lacewing larvae at controlling insect pests on plants. Other hoverfly larvae feed on rotting wood and some are aquatic.

Hoverflies are common, often colourful, and easy to recognize if you know what to look for. They are often mistaken for bees, bumblebees and wasps, and that is no accident. Adult hoverflies are defenseless, but by imitating stinging insects they trick predators into leaving them alone. Like bees they have a slim waist above the thorax, which is often brightly decorated with bee-like stripes.

So which insect should you avoid, and which is harmless?

The most obvious indicator of a bee or wasp is its long antennae. For example, take a close look at the wasp on the goldenrod (above left) or the bee on the daisy (further above). A hoverfly has much shorter, stubby antennae with a bristle. Sometimes they are hard to see at all, or look like no more than whiskers (above right).

Another important characteristic of hoverflies is that (like all flies) they have only one pair of wings. All that remains of the hind wings is a pair of small knobs called halteres, which they use for balance. Bees and wasps are typical insects, having four wings. However, they are transparent and the bee folds them over its back when not in flight, so the two pairs are often hard to distinguish.

I have sometimes mistaken a bee for a hoverfly. This error you do not want to make. Trust the antennae!

Another difference you might be able to see is in the mouth parts. Most flies have a proboscis with spongy pads at the end for soaking up food. Like most insects they also have mandibles, but these are much smaller. Again, bees are more typical, with larger jaw-like mandibles. However, these are often hidden.

So take a closer look at that bee, which might not be a bee! As often as not, what appear to be native bees or wasps are actually hoverflies. You have nothing to fear from them. And in beginning to notice, you will appreciate the great diversity of insects pollinating our plants.

Hoverflies make up a family called Syrphidae. According to the Canadian National Collection of Insects, Arachnids and Nematodes, northeastern North America has 397 species of hoverfly. Their website has a photo gallery to help identify some of them. BugGuide shows images of many of the 813 species in North America. As many as 6,000 species have been described worldwide.

Some species are tiny, like this one I photographed, which was only a few millimetres long. If you spot a glittering fleck darting gracefully around the flower garden, it might be a hoverfly.

There has been little research on hoverfly populations, except on certain species known to be rare and endangered. However, many experts suspect insect populations in general have been declining due to the widespread use of pesticides. The most important evidence comes from the well-documented and dramatic decline of a group of bird species known as aerial insectivores, which includes swallows, swifts, flycatchers and a few others. This phenomenon is poorly understood, but probably indicates a loss of insects for them to feed upon.

Gardeners and farmers can help by providing habitat for beneficial insects. Hoverflies are going crazy around the parsley blooming in my garden right now in mid-July. I have often seen them on tansy and goldenrod. Some other plants said to attract them are buckwheat, alyssum, candytuft, and yarrow.

Midsummer is a great time of year to look for hoverflies wherever summer wildflowers bloom along roadways and bicycle paths. But hoverflies are also some of the first pollinators to appear in early spring. So look before you duck!

Hoverfly on crocus

1 thought on “Know your hoverflies

Leave a Reply

Your email address will not be published.