One Fly Gardeners Should Learn to Appreciate


A typical hoverfly. Photo:

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!


Where Have All the (Lily) Beetles Gone?


Lily beetles are so brightly colored you can scarcely miss them. Photo:

I usually write this blog to answer other people’s gardening questions, but today I have one of my own. 

What has happened to the scarlet lily beetle (Lilioceris lilii)? I saw very few in my garden last year and none at all this year. In previous years, they were so numerous it really wasn’t possible to grow lilies (Lilium spp.) without applying some method of control.

The bright red insects would normally be hard to miss: they really stand out against green lily leaves, plus the damage they cause, chewed leaves and flower buds, is pretty obvious. 

Reader Rebecca Baker, from Montreal, also in my province, but 250 km (155 m) to the west, reports the same thing.

have seen lily beetles this year, though: in Ottawa, yet another 200 km (125 m) further west. While visiting the Ornamental Gardens at the Experimental Farm, I saw a (yes, just one!) lily beetle and a few chewed on leaves. So, the lily beetle hasn’t entirely disappeared.

The Ornamental Gardens in Ottawa still have lily beetles. Photo:

Weather Or???

In all likelihood, this is simply a weather-related phenomenon. We’ve had two very hard winters in a row in North Eastern North America: the winter of 2017-2018 was extremely cold, with frost descending to unheard of depths in the ground. Temperatures during the winter of 2018-2019 were not as extreme, but it came exceptionally early and lasted exceptionally long. Maybe the beetles weren’t able to survive such conditions. 

Tetrastichus setifer parasitzing a lily beetle larva. Photo: Tim Haye,

But there is also the possibility that one of the beetle parasites released to help control the lily beetle have finally kicked in. Various parasites have been introduced in the US and Canada to try and manage the lily beetle, including a parasitoid wasp (Tetrastichus setifer) and an ichneumon wasp (Lemophagus errabundus), as the scarlet lily beetle, of Eurasiatic origin, has no natural predators or parasites in North America. The two predators been shown to be very effective locally and there are signs they’ve been spreading. 

So, I have two questions for readers. 

  1. Have you noticed any decrease in scarlet lily beetle numbers?
  2. If local numbers have dropped, do you have any idea why?

Just click on Leave a Reply at the bottom of this page and let me know. Please indicate where you live: that will give a better portrait of where the lily beetle are thriving and where they are decreasing.

Thanks for your help!

Corn Slime Fixes Nitrogen… And May Save the World!


Aerial roots of Sierra Mixe corn. Photo: Jean-Michel Ané

Getting nitrogen into soils in a form plants can use has long been major problem for farmers and gardeners. But an ancient landrace of corn or maize (Zea mays) has been discovered that gets its nitrogen from bacteria feeding on the slime or mucus its roots produce.

Nitrogen (N) is abundant in the atmosphere and plants need it for their growth, but they’re unable to absorb it from the air. Billions of dollars are spent annually to produce nitrogen-rich fertilizers that plants can absorb through their roots, causing numerous environmental problems, both in its production and its use, so wouldn’t it be wonderful if plants could collect nitrogen on their own? That would certainly reduce the nitrogen pollution that’s become one of the biggest environmental problems around the world.

Of course, some plants do harvest their own nitrogen … with a little bacterial help.

Legumes, especially, including well-known food plants like peas and beans, are renowned for their ability to form symbiotic associations with nitrogen-fixing Rhizobium and Bradyrhizobium bacteria living in nodules on their roots. They give the bacteria a bit of sugar; the bacteria give them nitrogen. Everybody wins! A few other plants, like sea buckthorn (Hippophae rhamnoides) have likewise developed symbioses with nitrogen-fixing bacteria, but the vast majority of plants have to get their nitrogen from the decomposition of plant and animal products … or fertilizer!

Nitrogen-Fixing Corn

Now, however, a strain of corn has been found that also has a symbiotic relationship with nitrogen-fixing bacteria. This tall-growing (16 to 20 feet/4.5 to m high, twice the height of modern corn varieties), odd-looking traditional corn from the Mixes District of Oaxaca (southern Mexico), now being called Sierra Mixe, has been grown for hundreds, possibly thousands, of years. This is one of the areas where the corn was first developed from the wild grass teosinte some 7000 years ago. Sierra Mixe corn is adapted to poor soil, where it thrives without the use of fertilizer. And this it does through nitrogen fixation. 

It took nearly 30 years of study fully to understand what was going on, from the discovery of the landrace by Howard-Yana Shapiro (now with Mars, Incorporated, a major sponsor of the study) in the 1980s to today’s team, with Alan B. Bennett at the helm, at the University of California, Davis.

The slime coating the roots hosts beneficial bacteria. Photo: Jean-Michel Ané

This corn produces numerous pink and green aerial roots from its stem nodes and these are covered a sort of clear, gelatinous mucilage. It turns out nitrogen-fixing bacteria settle in the slime and pull nitrogen from the air, then share it with the corn, contributing from 29% to 82% of the nitrogen its uses.

Now, the question is: can this ability be bred into standard corn? If so, will the nitrogen-fixing capacity be widely adapted (corn is grown in an extensive range of environments all over the globe)? And does it exist in other cereal crops or can it be introduced into them? If so, can its effect be intensified by careful breeding? 

Corn is already the most widely produced grain in the world (1,099 million metric tons are grown annually), followed by wheat (734 metric tons) and rice (496 metric tons). If all three produced most of their own nitrogen, that would certainly lighten the load on the environment!

For more information on the study behind this discovery, read Nitrogen fixation in a landrace of maize is supported by a mucilage-associated diazotrophic microbiota

A Watering Basin for New Plantings


Watering basin around a newly planted tree. Photo:

To ensure proper watering the first year after planting, that is, the year in which plants are settling in and will need more water than when they are fully established, why not form a watering basin around each new plant?

This technique is used mainly with trees, shrubs and conifers because they tend to be slower to establish than herbaceous plants and also because they are usually a good size at planting and therefore require a greater quantity of water each time you irrigate. However, it can also be applied to any plant, especially if it’s in a situation where it is likely to need frequent watering.

A water-holding basin is simply made of a berm of soil up to 6 inches (15 cm) high all around the root ball. When you water, simply fill the basin with water. The water will then percolate into the soil exactly where the plant needs it!

When the plant is well established, usually after a year, just remove the basin and then the plant will benefit from the same watering as neighboring plants. Besides, after the first year, the roots will have (hopefully!) outgrown the size of the basin and water should be more widely applied to encourage continued expansion of the roots.

Just apply mulch over the watering basin. Ill.:

The presence of a watering basin doesn’t mean you can’t mulch your new planting. In fact, mulching is always wise, helping to keep the soil more evenly moist and preventing weed development. Just cover the soil in the basin and even the berm itself with 3 to 6 inches (8 to 10 cm) of your favorite mulch.

Adapted from an article originally published on August 27, 2015.

Toad Exit From Window Well


Always provide some sort of exit for animals from a window well. Ill.:, &, montage:

Last fall I was horrified to find a desiccated toad in my window well. Obviously, it had fallen in at some point over the summer and hadn’t been able to get out. 

Not wanting to repeat the experience (toads are one of the gardener’s best friends!), I propped up a plank against the well wall at about a 45-degree angle for use as a toad ladder. You could do the same with a log or build a toad staircase of old bricks in one corner. Just be sure to provide something for them—and for other small animals—to escape!

Strange Growths on Tomato Stems


Aerial roots on a tomato stem. Photo:

Question: Some of my tomato stems have strange bumps on them. I’m afraid they might be some sort of insect eggs or maybe mushrooms. Should I pull these plants? 

An Anxious Reader

Answer: No, just leave them alone.

What I see in your photo are just the beginnings of aerial roots, also called adventitious roots. They’re perfectly normal. Some tomato plants produce them readily, others not at all. Growing conditions seem to be a factor as well: they can actually grow considerably, to an inch or so (2–4 cm) long under high humidity.

Aerial roots are absolutely not harmful and you need do nothing about them. If they’re near the ground, you could even layer them, that is, cover them with soil, encouraging them to develop into full roots, thus giving your plants access to extra moisture and minerals. Also, you could take cuttings of stems with aerial roots and grow the new plants, although in all but the most tropical climates, that’s rather pointless, as the new plants won’t have time to produce fruit. 

Essentially, they’re a relic from the time tomatoes were wild lianas growing in tropical South America, a sort of back up strategy allowing them to reroot if they were damaged or knocked to the ground.