When winter settles in and bitter winds howl, I marvel at the ability of animals to survive our harsh winters. We know mammals hibernate and hoard, and birds migrate, but what about bees and butterflies? How do they do it?
Pollinator Strategies to Survive Winter
Pollinators, the small creatures responsible for one out of every three bites of food we eat, employ several strategies to survive winter.
Honeybees huddle together in winter in a carefully organized, compact ball. The interior bees generate warmth by vibrating their wing muscles. The outer bees remain motionless, acting as an insulation layer. The honeybees take turns enjoying the warmth in the middle of the huddle and then move to the outside. The colder the temperature outside, the tighter the cluster.
Native bees and butterflies employ other strategies to overwinter. Most survive not as adults, but in egg, caterpillar or chrysalis form in a hibernation-like state called diapause, a dormant state that allows them to withstand cold temperatures.
Most of New Hampshire’s native or wild bees spend the winter in their nest cells as pupae, emerging as adults the following spring or summer. Their nest cells are either in the ground or in cavities. Ground-nesting bees use loose soil and leaf litter. Cavity-nesting bees, representing about one-third of native bees, use hollow plant stems or holes in wood left by wood-boring beetles.
A few species migrate. The adult monarch butterfly heads south in the fall in a 3,000-mile migration to warmer climates in Mexico and California. The painted lady butterfly also migrates more than 1,200 miles on the way to their wintering grounds in the Southwest US and Mexico.
And lastly, a few species overwinter in their adult form. The queen bumblebee shelters in rodent burrow holes under the ground, insulated by a layer of leaves. The Mourning Cloak butterfly shelters under bark or in rock crevices, avoiding freezing by replacing the water in its body with antifreeze compounds which supercool its bodily fluids and tissues. Other butterflies in NH which overwinter in their adult form include Eastern Commas, Question Marks, and Milbert’s Tortoiseshells.
Winter Homes for Pollinators
Non-migrating bees, butterflies, beetles and other pollinators need cover to protect them from harsh winters. They survive by using natural shelters:
- Hollow canes and dead flower stalks of perennials are secret winter homes for butterfly species in the caterpillar and egg stages
- Leaves on the ground provide insulated hideaways for many pollinator species, including the wooly bear caterpillar (the larva of the Isabella tiger moth)
- Dense vegetation hides chrysalises of butterflies like the swallowtail, whose chrysalis is camouflaged to look like a leaf or twig.
- Old wood and bark are used by some of our native bees, including leafcutter and mason bees, as well as butterflies overwintering in the adult stage and by the caterpillars of species overwintering in a pupal form
- Undisturbed soil is the year-round home of many wild bees, who may be solitary or live in small colonies.
Four Ways to Help Pollinators Overwinter
So what can you do to provide winter shelter to bees, beetles, butterflies and other pollinators?
Consider allowing some wildflowers and debris to remain in and around your yard. Specifically:
- Don’t give away or compost your raked leaves! Keep them in your yard. Autumn leaves provide great mulch and great cover for overwintering insects (e.g., luna moths disguise their cocoons as dried leaves, blending in with real leaves). Spread them about 2” high on all your garden beds and place branches over them to keep them from blowing away. Place the rest in the woods.
- Postpone pulling up your dead annuals and perennials until spring. They’ll trap whatever leaves blow by, creating their own enriching mulch while shielding insects throughout the winter.
- Don’t disturb areas of bare soil where many wild bee species, including bumblebees, overwinter in small nests. The majority of native bees nest in the ground in a sunny spot that doesn’t flood.
- Leave dead logs, where bees such as the bright green sweat bee may overwinter under peeling bark.
For those of you who think this may be too messy, consider cleaning up just the front edge of the most visible areas and leave the back section until spring. Your eyes will be drawn to the neat edge and you will save your own energy while providing critical winter habitat and shelter for the beautiful moths, butterflies, pollinators and insects that you work so hard to support in the warm months. Your overwintering pollinators will thank you by emerging in the spring and delighting you all over again.
- UNH Extension: How to Help Collapsing Insect Populations (May 2019)
- Pollinator Pathways, a cross-town effort supported by several NH conservation commissions
- UNH Extension: Pollinator Habitats
- Connecting the Dots for Pollinator Conservation | Event Recap (3-minute video)
- Native Plant Trust: Ecological Gardening
Vicki J. Brown traded life as a marketing executive in Boston for NH’s woods, waters and wildlife in 2016. Today, she consults with mission-oriented organizations in healthcare and the environment. A Natural Resources Steward and volunteer for the Coverts and NH Fish & Game’s Wonders of Wildlife programs, Vicki is slowly turning her lawn into pollinator and wildlife habitat. @bostonflamingo