Saturday, June 6, 2009

Gardening for Pollinators meets Lord of the Flies

Another week, another threatened frost: such is Spring in a Zone 3 Bug Garden. Oh well, I should stop whinging and just get on with it. The HBG was first envisioned as a home for pollinators, which I suppose we thought of as mainly bees and butterflies. Well, not really, since at one time or another we have both taught pollination ecology, but embryonic bug garden thoughts aren’t necessarily very deep and butterflies, bees, and flowers was the general idea.

Not that we wanted to see lots of honeybees (another Australian anti-alien bias), but with the spread of the varroa bee mite and the emergence of the mysterious Colony Collapse Disorder, our primary pollinator has been on the ropes for some time now. In Alberta, a harsh climate and marauding bears mean that the only honeybees you are likely to see come from well defended bee keeps. Apparently no one near us has a backyard hive, because Apis mellifera is a rare visitor. That is too bad if you like cherries, saskatoons, apples or other home-grown fruit and vegetables, but there are alternative pollinators that have been attracting attention now that the tried and true honeybee is on the wane. There’s even a web resource page devoted to ‘Alternative Pollinators’ and, although a very high proportion of its links are broken and the functioning links often lead to questionable sources of information, the list supports the assumption that bees + butterflies = alternate pollinators.

Alberta has ‘native’ bees that can hold their own against the climate. Bumblebees (Bombus), leafcutter bees (Megachile), sweat bees (Halictidae), and digger bees (Andrena) are all reasonably diverse here. Our goal was to make the HBG their home by providing a more or less continuous bloom, and to reap our payback in produce. In that, I think we can claim some success, but it is small. Bees need more than flowers, and in particular, they need nesting sites. We did think of this a bit, e.g. planting shrubs with hollow twigs, but the most important of the alternative bee pollinators here are ground nesters and rodent burrows and bare patches of untilled soil aren’t exactly extensive in the HBG. Most of these bees are solitary and having a few dozen nesting in your yard isn’t going to do much for spring flowering fruit, especially since the most efficient of these, the leafcutter and bumblebees, are mostly summer visitors.

Leafcutter bees are a bit of a mixed blessing, since they certainly live up to their name, but they more than pay back the linings of their nests with efficient pollination of most of the veggies in the garden. Unlike most pollinating bees, megachilids collect pollen on their long body hairs and not on special pockets on their hind legs.

Bumblebee colonies take a while to grow and there is a distinct hiatus around now when the first brood must be pupating and the queens taking a well deserved rest. Add to that yet another late, cold spring and the result is cherry trees covered in silent blooms.

Of course bees are not the only pollinators. A variety of other Hymenoptera (ants, sawflies, wasps), beetles, butterflies, and flies come to flowers – or at least to certain kinds of flowers. Spreading, open inflorescences like those found in the carrot family or composites can accommodate a high diversity of insects out for a good feed. Surprisingly, two-winged flies (Diptera) are perhaps the most abundant and diverse of these alternative pollinators. The flower or hover flies (Syrphidae) are perhaps the best known of these floral frequenters. In his "Insects - Their Natural History and Diversity" Steve Marshall says we should treat syrphids as "honorary butterflies" for their bright colours, expert acrobatics, and abundance in familiar environments. Such honours do seem to have been bestowed in the UK, where pocket guides to hoverflies are available and such giants in the pantheon of bug gardeners as Jennifer Owen have done much to document syrphid diversity and abundance in urban gardens. Alas, no such guides or documentation seem to be available here (John, are you listening?).

Many syrphids mimic hymenopterans with a sting such as hornets and bees, which no doubt makes hanging around flowers a bit safer. Beeflies (Bombyliidae) could be said to do the same and often have their mouthparts drawnout into elongate straws for sipping nectar in the deeper flowers. No such advantages in camouflage are apparent in what seem to me to be the creepiest of the dipterons that frequent flowers - blowflies (Calliphoridae), especially species of Lucilia (bottom two pictures in fly plate) that would seem more at home on carrion. Astilbe seems to be especially attractive to these flesh flies.

So if you just want flowers and happy pollinators, and don’t mind a preponderance of flies, think large, open inflorescences like astilbe, goldenrod, butterfly weed, yarrow, daisies, caraway, lovage, and the like. If, however, you want apples, cherries, saskatoons, currants, beans, peas, tomatoes, peppers and anything else that requires some skilled pollination, then you need bees, and bees need a home as well as food. I suppose it is well past time that I started learning what bumble and digger bees need to make a home.


  1. Great shots by Heather. I particularly like the Megachile on the snapdragon--it looks like it was taken from inside the flower.

    Do the bee condo's show any sign of use yet?

  2. No sign of habitation in the bee condos yet, but the bamboo one is very attractive anyway.