Beautiful Native Plants

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Wednesday, February 15, 2017

Pollinators and the Garden in Winter

Man-made bee houses
Good replacement for holes in old logs
©Beatriz Moisset
Do you ask yourself: where do pollinators go in winter? We see them through the warm seasons visiting flowers and doing their invaluable job. But, then what happens to them? Putting aside the few, such as hummingbirds and monarch butterflies, which fly to better climates, all the others find a secluded place to spend the cold months. Like hibernating bears, many fatten themselves by stocking up on supplies and then go to sleep. Others rest as eggs or in an immature state such as a larva or pupa. Either way, they need a sheltered space safe from predators, parasites and excessive cold.

I know that some gardeners, with the best of intentions, destroy these vital shelters. It may be a good idea to take a look at all the places used by pollinators during the winter. This is one case in which a little untidiness may be a good thing.

Most bees are ground nesters; this means that they build their nests in the ground, preferably a bare spot, dry and sunny and not subject to flooding. Sometimes there is a patch large enough for a whole town of nests; other times, just a few square inches of soil free from vegetation fill the needs of one enterprising bee raising a family. The mother bee dies at the end of the season, her mission accomplished. Her babies will emerge from the nests next spring.
Ground nest of a digger bee
©Beatriz Moisset

Not anthills but a small town of
Lasioglossum bees
©Beatriz Moisset

Bumble bees find some nook or cranny underground, perhaps under a tree root, a log, or even an old wall. The difference here is that the overwintering pollinator in this case is the adult, already mated and fertilized female which will start a whole new colony next spring.

One of my favorite bees, Augochlora pura, doesn’t nest underground. Instead it finds a dead log, whose bark is beginning to peel, and builds its nest under the bark. The younger generation emerges at the end of summer. They mate, and the new bees find shelter, once again, under loose tree bark. Many old dead logs serve as wintering shelter for this bee.

Two Augochlora pura females
getting ready for winter in November
©Beatriz Moisset

A sleeping beauty under bark in mid January
©Beatriz Moisset

Sleeping Beauty’s castle, old logs
©Beatriz Moisset
Other bees, including mason and leaf-cutter bees, use hollow twigs or holes dug by beetle larvae in trees. Bee houses that imitate these conditions are gaining popularity among gardeners and mason bees readily accept them. This is becoming a necessity in our suburban gardens, where old trees with beetle holes are rare. Clumps of dried grasses or the hollow canes of plants such as hydrangea or brambles are also valuable to nesting bees if they are allowed to stand through the winter and early spring.

Hollow twigs are a winter haven
to many pollinators
©Beatriz Moisset

Bees are not the only pollinators. Butterflies and moths do a good job too; so let us take a look at a couple of them.

 Fritillary caterpillars feed on violet plants. In the fall, when the adult butterfly is ready to lay its eggs, these plants are wilting or totally gone. The female lays its eggs near the remnants of violet plants or in the most likely places for violets to grow. Even if many eggs are lost, there are enough left to maintain the populations year after year. The curious thing is that the eggs hatch in the fall when there is nothing for the caterpillars to eat. So the tiny newborns bury themselves a little deeper and go to sleep until the next spring. By then, their food is ready and waiting for them.

Hummingbird moths (Hemaris), those colorful tiny pseudo-hummingbirds (I have seen many people fooled by them) have a different strategy. Their eggs hatch in the summer and the caterpillars feed on one of their favorite plants. They are not very choosy, from honeysuckles, to viburnums, to blackberries; all of them are good for the several species of hummingbird moths. In autumn, the fully grown caterpillar drops to the ground, buries itself under the leaf litter and becomes a pupa. Now it is ready for winter.

A patch of leaf litter serves as a winter home
to some pollinators
©Beatriz Moisset
Numerous variations on these general themes exist. Not just pollinators, but also a number of other insects, some of them beneficial predators of pest insects, take advantage of the mentioned wintering spots. We can conclude that: bare spots, dead logs, dried up grasses or other shrubby plants and leaf litter are all vital to pollinators and to other creatures, all of them important components of a garden ecosystem. The perfectly manicured garden may appeal to a certain idea of esthetics but it is a monstrosity from the ecological point of view. Some of us need to readjust the way we view a garden.

There is great beauty in the mechanism of how an ecosystem works. I relish this beauty so I find it easy to accept the visual impact of an “untidy” garden in need of some raking, re-sodding, log removal, leaf litter removal, etc.

Also see:
Helping Native Pollinators Winter Over Sierra Club

© 2011, Beatriz Moisset. First published in Native Plants and Wildlife Gardens, 2011