Not every pollinator has the same nesting requirements. Following are some tips on how to provide nesting sites for a variety of pollinators. Keep in mind that nesting habitat for bees as well as egg-laying habitat for butterflies, moths, and other insect pollinators should be located close to good foraging habitat.
To provide nesting habitat for ground-nesting bees, maintain areas of bare or sparsely vegetated soil. Ground-nesting bees prefer loose, well-drained soil in a sunny spot. Some species nest in flat areas, while others prefer earthen banks, so provide a variety of areas with different slopes if possible, preferably south-facing to maximize exposure to the sun. In areas with healthy, friable soil, clear an area of vegetation at least several yards across. In places where the soil is compacted or otherwise unsuitable, dig out a section 2 to 3 feet deep and replace with sandier loamy soil that is soft enough to dig in but stable enough that burrows won’t collapse. Potential nesting habitat can also be provided with soil-filled planters. Once you have established a nesting area, make sure it does not become overgrown with vegetation or shaded out. To prevent the soil from becoming compacted, do not walk over the area, and do not till or dig it up as that will destroy the nests.
Protect nesting sites for wood-boring bees by keeping dead trees, snags, or fallen logs on the land. Some bees will build their nests in old beetle tunnels. In addition, minimize pruning of pithy shrubs, such as elderberry, sumac, or hydrangea from year to year.
Artificial nest sites
In areas where there does not seem to be sufficient natural habitat, you can provide a variety of nesting materials that bees will use. The Xerces Society pdf, Nests for Native Bees includes plans for the following nest types.
Bee nesting blocks: Some cavity-nesting bees will use manmade nesting blocks, including the blue orchard bees used commercially to pollinate apple orchards. To construct a nest block, use preservative-free wood—4x4s are adequate for blocks with only small nesting holes, but 4x6s are required for larger nesting holes. You can also drill various-sized holes in stumps or old logs.
Making holes of varying depths and diameters in the nest block is often recommended to attract a variety of bee species. There is no “correct” way to do this, so it’s worth experimenting to see what you get. Nesting holes should be relatively small: 3/32 to about 3/8 inch. Holes 1/4 inch or less should be 3 to 5 inches deep, while holes larger than 1/4 inch should be 5 to 6 inches deep. The block must be closed at one end and holes should be smooth and placed in from the edge at least 3/4 inch.
Be sure to locate the nest block where it is protected from direct rain and faces south or southeast so it is warmed by the morning sun. Place the block on a firm support 2 to 6 feet above the ground. Bees use landmarks to navigate to and from their nest, so putting the nest block near a large object (like on a shed or tower) will help them navigate.
Stem bundles: You can also bundle pithy, soft-centered stems together in small packets. Good plants to use include sumac, box elder, elderberry, raspberry, and even phragmites, Japanese knotweed, or old bamboo plant stakes—anything with hollow stems. Cut sections just below a node, place them so that the open ends all face in the same direction, and strap them together. Hang the bundles outside in a sheltered location horizontal to the ground, facing the morning sun.
Bumble bee nesting boxes: Bumble bees, which naturally seek out old underground rodent nests or cavities under grassy tussocks, may find specially constructed boxes suitable for nesting. Typically, they are made of wood and filled with nesting materials such as dried moss or horsehair stuffing from old furniture. It’s not clear how well these artificial nests actually work, but building one can be a fun student project and help raise awareness about the needs of bumble bees and other native pollinators.
Care of artificial nests
Nesting blocks and boxes as well as stem bundles should remain out during the season but can be brought into a protected area for the winter. To prevent disease transmission, make sure you clean out nesting boxes or bundles after the new bees emerge in spring, or replace them each year.
Butterflies and Moths
To provide egg-laying habitat for local butterflies and moths, you need to become familiar with the food plants required by their larvae. The caterpillars of each species have specific host plants. Although adult spicebush swallowtails nectar on many different flowers, for example, their caterpillars feed mainly on the leaves of spicebush (Lindera benzoin). The North American Butterfly Association website has a good list of caterpillar plants for butterflies.
Another excellent resource is Caterpillars of Eastern North America: A Guide to Identification and Natural History by David Wagner.
Butterflies and moths lay their eggs directly on their larval food plants, so make sure these species are in close proximity to nectar sources for adults. Occasionally, butterflies and moths will pupate on their food plant, but often they move to another sheltered location or in the leaf litter to pupate. Maintain undisturbed habitat nearby where the caterpillars can safely pupate before emerging as adults.
Insect Pollinators in General
To retain a diversity of nesting materials, avoid excessive raking and manicuring.
Different bee species use different materials to construct the brood cells in which their young develop and to seal nests. For example, leaf cutter bees may use bits of leaves from various shrubs, while other bees may use mud or fine pebbles.
After spending the winter as far south as Central America, the Ruby-throated Hummingbird returns north to nest. Their tiny nests are constructed of plant fibers and lichen woven together with spider silk. Like bees and other insect pollinators, they require feeding and nesting habitats in close proximity. Ruby-throated Hummingbirds are found in a variety of habitats, but according to the recent New York State breeding bird atlas, they rarely nest in heavily developed areas.