Pollinator Garden Basics

A Green-Headed Coneflower provides nectar for multiple Sweat Bees, a Bumblebee, and Orange Mint Moth.

     There are over 200,000 species of pollinators worldwide. These include such diverse animals as bees, wasps, butterflies, moths, flies, beetles, and hummingbirds. We owe them much, as it is often said that one out of every three bites of food we enjoy is due to the direct actions of an animal pollinator. In fact, three-quarters of all plants, regardless of whether we eat them or not, depend on animal pollinators in order to reproduce. There are many basic things we can do to make our gardens and landscape more pollinator friendly:

•      Avoid using pesticides and/or herbicides.

•      Plant for continuous blooms throughout the seasons (so you have continuous food).

•      Use mass plantings (they’re easier to see by pollinators flying by)

•      Include host plants for caterpillar and oligolectic plants for bees (the native plants 1/5

        of our native bees evolved with and need in order to reproduce).

•      Provide basking sites (they all need to warm up).

•      Consider wet mud spots to serve as puddling areas for butterflies, mud plots for

         mason bees/wasps.

•      Try to locate your garden in the sunniest location you have for the most blooms.

•      Consider flower color & shape (white, yellow or blue composite flowers are often

        best).

•      Avoid double-flowered or other cultivars (cultivars are chosen for traits people want; 

   evolution chose what the pollinators want).

•     Leave old stalks, if not diseased, to overwinter. If you can cut stalks to a foot or so

        high and leave them for the new growth to grow over, you can provide nesting spots

        for insects such as bees, of which 30% nest in places like old stalks. It will still look

        neat, but provide nesting platforms throughout the year. If you resist the urge to

        clean up and remove fallen leaves, you also provide good habitat.

•      Go Native!



A Goldenrod is covered in small pollinators.

 

Why Choose Natives?

 

-    They provide more food/shelter for the animals with whom they evolved. 96%

       of terrestrial birds feed their young caterpillars (and sawflies) as their major food source,

       particularly while nesting. All 17 of our bat species feed on insects preferring moths

       (which of course are adult caterpillars).

 

-    They are preferred by native wildlife (with whom they evolved). Indeed many are

       necessary as host plants for caterpillars and 1/5 of our bees.

 

-    Given that most insects lay large number of eggs, supplying the plants they need can

       make a big difference locally. Of all the insects that feed on plants, 90% are specialists

       needing the native plants they evolved with, and many of these are pollinators such as

       butterflies and bees.     

 

-    They are adapted to our environmental and soil conditions in which they evolved.  

 

-    There are so many to choose from adapted to just about every growing condition (over

       1700 species in NoVA alone).

 

-    The same plants can have multiple uses (aesthetics, edible landscaping, herbal, wildlife

       gardening, etc.).

 

-    They are attractive!

     
     So do your part for pollinators and other wildlife by following these guidelines, most especially by going Native!

A Bumblebee and Monarch Caterpillar share a Swamp Milkweed.

Happy National Pollinator Week!

A Bumblebee, Metallic Sweat Bee, and Orange-Spotted Mint Moth share a meal on a Green-headed Coneflower.

   Happy National Pollinator Week! There are over 200,000 species of pollinators worldwide. These include such diverse animals as bees, wasps, butterflies, moths, flies, beetles, and hummingbirds. We owe them much, as it is often said that one out of every three bites of food we enjoy is due to the direct actions of an animal pollinator. In fact, three-quarters of all plants, regardless of whether we eat them or not ,depend on animal pollinators in order to reproduce.
     When thinking about planting things to benefit our pollinators who benefit us so often, a critical thing to consider is the use of native plants. Studies show that native plants are four or more times more attractive to native pollinators than exotic plants. This, of course, makes perfect sense since these plants and animals evolved together, sometimes to the point that one cannot exist without the other. Many caterpillars for example cannot survive without their specific native host plant to feed on. About one out of every five of our 450 native bees in the Mid-Atlantic area need the specific pollen of certain native plants or they cannot reproduce. Just any flower or plant simply won't due.

A Hibiscus Bee (Ptilothrix bombiformis) digs its nesting hole. While it can visit many flowers, it needs pollen from plants in the hibiscus family or it cannot reproduce.

     So the most important consideration is to plant plants that are locally native. These plants are not only adapted to grow in this type of habitat, but are what the pollinators have been using for thousands of years. It is also always best to use straight wild species, rather than cultivars or nativars which have been selected for certain traits. When we plant a flower that has been bred to appeal to us through a novel color or look, it may not have the same appeal to the pollinator its parent plants originally evolved with. What might be attractive to us may not be attractive to pollinators, some of which see flowers through different spectrums or look for certain traits in them. This is especially true of plants bred to have double flowers or blooms with extra large petals, since they often sacrifice nectar/pollen for the extra showy flowers. To remove any doubt and provide maximum habitat value, go native.



Multiple Great Spangled Fritillaries nectar on Swamp Milkweed, the host plant for Monarch butterflies and 11 other caterpillar species. With 15 species of milkweed alone in Virginia, there's a native one for just about every growing condition, not just swamps.

     Also something to consider are the multiple uses you get with native plants. Many exotic plants may have a pretty flower that may (or may not) provide nectar for a short time each year while blooming, but it otherwise provides little habitat or nutrition for pollinators or other native wildlife. Take the Chinese Aster (Callistephus) for example. It is a pretty flower, comes in many color forms and is widely planted (and has escaped and naturalized into some areas). The blooms on some varieties provide some nectar and pollen to a few pollinators for a short bloom time each year. But only two species of caterpillars have been recorded as feeding on it. It is for the most part and for most of its plant life a barren habitat for wildlife, taking the place of what might have been a much more beneficial native plant.
     Contrast that with one of our many (Virginia alone has 43 different species) colorful and attractive native asters, many adapted to a variety of growing conditions. Now you have flowers that not only provide attractive flowers for the garden and a similar look, but also serve a habitat and food function. In addition to pollinators visiting them, most also supply seeds for birds such as finches and sparrows. But 109 different caterpillar species have also been documented feeding on asters. These in turn feed the vast majority of our nesting native birds (96% of terrestrial birds feed on insects, particularly during the nesting season, most of which are caterpillars) and most of the 18 bat species found in our region (all of which are insectivores and many of which prefer moths over other insects). At least 8 different bee species need their pollen or they cannot reproduce.

A Pearl Crescent nectars on an aster, which also is the only food its caterpillars can feed on.

      So you can see how something as simple as choosing a native plant species can not only serve to provide for pollinators, but then serve many other habitat functions as well. So this National Pollinator Week, enjoy the pollinators in our gardens, farms, and parks. Include locally native plants in your gardens. This way you too can help the pollinators who are always helping us.

A Syrphid Fly, a wonderful bee mimic, pollinating Tickseed Sunflower.

     In Arlington County, we try and make the vast majority of the plants we use natives for all the reasons stated above, it is part of our planting policy. This week serves as the two year anniversary that Arlington County made the Mayor's Monarch Pledge to commit to doing several different things to help monarch butterflies. We of course will continue to do many other things to help monarchs and so many other pollinators. Here's a look at the Bluemont Pollinator Patch one year later during National Pollinator Week in June of 2018: https://www.youtube.com/watch?v=PLu9pEFCpEo.

A pair of Long-Horned Locust Borer Beetles multitasking, feeding, mating and pollinating Goldenrod all at the same time.

     The establishing of Pollinator Patches and Monarch Way Stations is just one way to continue to support pollinator numbers. Please join us in supporting our pollinators by planting native plants when you can and taking pollinator needs in to consideration when you do things at home. 

A Sweat bee and Bumblebee sharing a Wingstem meal.

City Nature Challenge 2019 Results

     This year's friendly global citizen science competition, the City Nature Challenge, ended up with 159 cities competing! These cities tried to get people out making nature observations using the free iNaturalist application to take photos that were uploaded during a 4 day competition to see who could get the most people involved, make the most observations, and identify (through crowd sourcing) the most species. These could all later be data mined by researchers and others to provide information for various projects.

     This year the Greater Washington DC Region once again did very well, despite there being more cities competing this year from the 68 that participated last year. Reporting 29,976 observations, the DC Region came in 10th overall, behind, in this order: Cape Town, La Paz, San Francisco (who helped start the challenge), San Diego County, Tena (Ecuador), Klang Valley (Malaysia), Dallas/Fort Worth, Los Angeles, and Hong Kong. You can find out more about the City Nature Challenge, including details of the leaderboard here: http://citynaturechallenge.org/ . For a summary from the Academy of Sciences, look here: https://calacademy.org/press/releases/city-nature-challenge-results-in-nearly-1-million-wildlife-observations.
     As many other parts of the world have much greater biodiversity, the DC Region placed quite well coming in 15th on the globe with 2,261 species tallied. But where our area really stood out was in participation. The 1,259 particpants who entered their observations placed DC 4th overall! Only the 2 original founding member cities of San Francisco and Los Angeles, followed by La Paz placed better. What a wonderful testament to the interest in nature and the willingness to participate in citizen science the nation's capital has to show!

A Nessus Sphinx Moth found in the Barcroft Natural Resource Conservation Area

     Locally, I'd like to feature Arlington, which while part of he DC Region team, did fairly well on its own. It contributed 4,635 observations of 803 species entered by 163 observers. The Mayapple was the commonly reported plant while the American Robin was the commonly reported animal.  It will take quite a while to go over all the individual species reported and see if any should be further investigated, but the data is now there to do so. More over, 3 Arlington County staff placed in the top 11 in the DC region for species tallied.
     I personally had my best City Nature Challenge ever, and am happy that I tallied 880 observations and topped the leaderboard with 430 species reported. That species count overall was good enough to place 25th in the whole global challenge.

     So lots of reasons to be happy: with how great the DC region did, how Arlington did, and my personal tallies. But more importantly, I am so happy that 159 cities decided they would participate, that 32,781 people entered 32,781 observations, entering data on 31,837 species. What a great commitment to citizen science, to pride in what nature is found close to them, and that they were willing to have some great fun while in this friendly global competition. Now I can't wait until next year!

    

Participate in the City Nature Challenge 2019!

City Nature Challenge 2019!

     A friendly global challenge was issued this year: Which cities could engage the most people to record the most observations of wildlife and plants, and find the most species over 4 days, April 26-29?  In last year's global event, 68 cities participated and tallied 441,888 observations by 17,329 people. This year is even bigger! There are over 160 cities worldwide who have answered the call!
     The first City Nature Challenge started as Citizen Science Day, with citizen science teams at the Natural History Museum of Los Angeles County and California Academy of Sciences challenging one another into what turned out to be an eight-day friendly competition in April of 2016 between Los Angeles and San Francisco, engaging residents and visitors in documenting nature to better understand urban biodiversity. It grew to 16 cities in 2017, and went international in 2018.
     The free iNaturalist app (https://www.inaturalist.org/) is now the standard way for bioblitzes and other citizen science (the involvement of the general public in scientific research and data collection) projects to record information and is what most cities will use for recording City Nature Challenge observations, including the team here in the Washington, DC Metro area. The beauty of the app is that with a simple uploaded photo, crowd sourcing can then help identify the organism and the observation is recorded so that worldwide any researchers can data mine the info they need. You never know what piece of data you could be providing some researcher somewhere in the world. You don't even need to know what you're reporting (though the iNaturalist app has a neat suggested identification feature to provide likely ID possibilities and there's a neat new Seek app that can help ID things on the spot (https://www.inaturalist.org/pages/seek_app) too!). This is due to the crowd sourcing that allows other perhaps more knowledgeable people to provide their ID skills. A short instructional video can be found here: https://vimeo.com/246153496



 

The DC Metro Area did very well indeed in this global event last year:

     Its 22,809 observations was 5^th place overall, behind San Francisco which started the competition 3 years ago (41,737 observations), Dallas/Fort Worth (34,218 observations), San Diego (33,448 observations), and Klang Valley/Greater Kuala Lumpur (25,287 observations). Just behind DC were Houston followed by New York. Coming in last was Palmer Station Antarctica which understandably only had 36 observations (but 27 species with only 3 people in Antarctica of all places!). Globally 124 new species were added to the iNaturalist data base that had not been present before.
     As far as participation, the DC region again did wonderfully! It came in 4^th place overall with 876 participants who made observations. This was behind San Francisco (1,532 observers), San Diego County (1211 observers), Boston (992 observers), and just ahead of Los Angeles (which also started the competition 3 years ago, with 855 observers). With over 40 planned DC regional events over the competition period, it turned out those group events really paid off.
     The DC Metro Area also did remarkably well with its species count, considering some tropical places have so much more biodiversity. The DC Metro Area came in 8^th overall with 1,855 verified species observed.

Among one of neat findings was this Southern Adder's Tongue Fern at Huntley Meadows Park

      Arlington had a good showing overall as well for the DC region it was included in. Of the over 40 DC Metro Area planned events, Arlington led or had a leading partner role in 25 of them. Within Arlington County itself, 134 observers tallied 3,957 observations and identified 644 species. The top observed species for Arlington were the American Robin (reported 46 times) and Virginia Creeper (reported 46 times). Some unusual sightings will need to be investigated and verified as they might prove to be very interesting. While some are positive, the observations of potential new invasive plants are also important to know about, and a few were indeed reported. Overall, a very respectable showing and demonstration of Arlington’s commitment to citizen science.

     This year, the DC area has over 124 events planned, with numerous organizations, local jurisdictions, and individuals planning to participate. You can find out more about the DC Metro Area events here: https://citynaturechallengedc.org/ (including Capital Naturalist events). The Arlington County sponsored events are here: https://parks.arlingtonva.us/nature-history/city-nature-challenge/ . More Arlington events sponsored by the Arlington Regional Master Naturalists here: https://www.signupgenius.com/go/60b0b4fa8ab22a31-arlington
     Whether you'd like to join one of these organized events or go solo, what great fun and discovery! What's not to like about that? So here's to the City Nature Challenge, as a fun way to make nature discoveries in our wonderfully diverse region while providing valuable scientific data! So please do participate!




Bee Nesting Structures

An Eastern Carpenter Bee and numerous mason bees make use of two artificial bee structures.

     About 30% of our region’s 450 or so bees nest above ground. Many do so in dead trees, borer beetle burrows, and in stems of plants with soft or hollow stems and piths like elderberry, sunflower, sumac, and blackberries. This is one more reason to leave garden plants standing through the winter, as many are housing insects in various parts of their life cycle, including pupating or adult overwintering bees. Ecologically minded gardeners don’t tidy up (unless removing diseased plants) until spring, along with of course planting non-cultivar native plants. Even better is to cut the tops off about a foot high, leaving the stems for bees and other insects to use for the following season. Since many bees need help in getting into a stem, the open tops are perfect for this. Native plants not only provide nesting and nectar sources, but 35% our native bees are oligolectic, needing the specific pollen of the plants they evolved with in order to be able to reproduce. 

An Elderberry shows signs of where woodpeckers have foraged for mason and other cavity nesting bees.

    These mostly solitary bees include Small Carpenter Bees (Genus Ceratina, about 24 species in North America, 4 locally), Large Carpenter Bees (Genus Xylocopa, only the Eastern Carpenter Bee, X. virginica, is common around the DC region, though the Southern Carpenter Bee, X. micans, has been found in southern Virginia), Leafcutters (Genus Megachile, about 130 species in NA), Mason Bees (Genus Osmia, about 150 species in NA, 27 east of the Mississippi, though several other Genera such as Hoplitis and Chelostroma are also often called mason bees), and a few other types which use cavities or take advantage of above ground structures.

A male Eastern Carpenter Bee nectars at a Swamp Milkweed. Many cavity nesting bee males have white faces. More on Eastern Carpenter bees: http://capitalnaturalist.blogspot.com/2014/10/carpenter-bees.html

     After planting native plants, limiting use of pesticides/ herbicides/fungicides, leaving garden bed plants standing throughout the winter, leaving some old stems standing cut a foot or so high, and allowing your lawns to have some clover and other perhaps weedy looking flowers, there are some other things that you can do to make your yard more bee friendly and appealing to many pollinators. In many parts, bee/insect “hotels” are becoming quite popular. 

An insect hotel geared for bees at Audubon Naturalist Society headquarters in Maryland.

     But you needn’t make things so extravagant, unless of course you want to. While there are numerous types of bees that will make use of artificial structures, mason bees are the most common, and luckily what works for them will generally work for others. Simply changing the size of the openings to the structures often is enough for the other cavity nesting bees (and many other insects). 

Blue Orchard Mason Bee, the most common native mason bee.

     Mason bees (including Osmia lignaria and others) are small, dark bees that do not live in large social hives, but are actually solitary (like most of our 4,000 species of native bees in North America). They tend to be primarily active in the spring. They also can work at lower temperatures than the introduced European honey bee. They are very peaceful, only using their weak sting if grabbed or trapped inside clothing and do not swarm. Although not honey producers, they are superb pollinators, especially under questionable spring time conditions. Individuals supposedly can visit more plants per hour and in many cases can be up to 90% more efficient at pollination than the introduced European honey bees. Mason bees also carry their pollen on their hair (scopa) underneath their body so often pollinate more flowers than honeybees that carry their pollen moistened in “baskets” on their back legs (leading to less pollen contact with another flower). This pollen also tends to be dry and pollinates easily where honeybees often use nectar to wet the pollen they carry so it does not fall off as easily to pollinate the flower. Mason bees tend to prefer flowering shrubs over plants but will visit whatever is available. Two introduced Japanese Horned Mason Bees are also becoming quite numerous in our area, and are the most likely ones you will attract. In the wild, orchard mason bees (as they are sometimes called) use hollow stems or cavities in trees to nest in (they do not make their own holes). Many commercially available bee houses with replacement tubes are sold for them to utilize. It is also quite easy to make some suitable homes for them. One simple way is to cut some bamboo, Phragmites (a good use for both these invasives), elderberry, and/or sumac at their nodes, hollow them out all the way to the node so one side is still sealed, and bundle them together (with the open ends facing one direction) for the bees to discover. Place them where they will get some sun in the morning and some shelter from the rain. The bundles do not have to be all even at the open end since that makes it even easier for the bees to orient themselves to their own nests. From 5-8 inches long is fine. Various entrance-hole sizes will work but a good compromise size is 5/16inch in diameter.

A structure supporting both blocks with drilled holes and bamboo built as an Eagle Scout project as part of a pollinator patch in Arlington Virginia.

     Another way is to drill some 5/16in diameter holes (or you can vary hole sizes) in some untreated pieces of wood (sections of 2x4’s or bigger is even better). Make each hole ¾ inches apart from any other on all sides. The deeper the holes the better (6 inches or so but again not all the way through) since female eggs are laid towards the rear of any tunnels. The more longer-lived females you have, the faster your population can grow. Luckily nesting bees show great nest fidelity and tend to try and use the same area each time. Place the pieces of lumber so they can get morning sun and some protection from the elements much as you would with the bamboo and other cut stems. Some large diameter wire screen across the front will help keep woodpeckers or rodents from eating them, but still allows the bees to do their thing (something smaller than chicken-wire).     
     Provide some moist soil nearby (preferably clay based) so they can construct their nest cells. Try to have your nesting structures for them out by mid-March around here since more female are produced earlier in the year than later. The bees tend to be active for just a little over a month each (each bee lays about 35 eggs) so you want to be ready for them. This works for most blue orchard bees, but there are many other different bee species. For this reason, some people experiment with different size holes to attract whatever local types might be around.  In the Fall, some people put the nests in a cool place like a shed to protect them from predators. Other people carefully remove the containers (straws or open plastic tubes often commercially) as they fill and put out fresh nesting holes. The stored containers should be placed right-side up with the mud-sealed openings towards the top, in a protected shed or other place that undergoes conditions similar to the outdoors.
  Care should be taken not to jostle them very much so as to not dislodge the developing young or eggs.  Some people even refrigerate them after September and “activate” them just before they need them for their orchards or plants. For more instructions on building or providing bee “homes” check out the Xerces Society: http://www.xerces.org/wp-content/uploads/2008/10/nests_for_native_bees1.pdf.

A commercial mason bee system consisting of cardboard straws with paper inserts that can be cleaned and replaced yearly.

     Commercially available systems and boxes are sold and most work fairly well. Most people agree that paper straw inserts and tubes will work, but some are better than others. Waxed paper tubes tend to keep the nectar from drying out and are an improvement and those made out of cardboard are even better. Wood is best since it offers the best protection from predators like Chalcid wasps but can’t be re-used too often without parasite problems (unless you use paper straw inserts in them). Bamboo and plant stems can crack and offer less protection from predators or parasites. The bees also prefer darker colors and you should also try not to clump too many holes or tubes together since the bees can get disoriented as to which exact hole is theirs. Some folks insert different color paper straws to help the bees find their own home easier or simply paint the edges different colors to help the bees orient themselves. Plastic straws do not work and lead to fungal problems.  
 

A Blue Orchard Mason Bee utilizing a commercial plastic bee box system which can be pulled apart for cleaning and has multiple colors to help the bees find their individual holes.

     Populations often build quite well from year to year. But there are issues with placing so many solitary bees so close together. This unnatural situation attracts many predators. More so, it allows for the build-up of illness, fungal issues, and parasites. For that reason many people change them out or clean them yearly. After several years, many also move the structures to new areas. All this helps with these high population issues. 
 

A Leucopis Chalcid Wasp searches for a place to insert her ovipositor to parasitize a mason bee tube.

 

A male mason bee covered in pollen mites. In large numbers, these can be harmful to bees. Populations can build up in colonies or when using the same holes/tubes each year.

      As mentioned, 2 nonnative Japanese horned bees (the Japanese Hornfaced Bee Osmia cornifrons and the Taurus Mason Bee Osmia taurus) are now quite prevalent and are the most likely mason bee to be attracted, as they are less picky about where they nest and reproduce quickly. Whether or not they are harmful to the native bees through competition for limited nesting sites or nectar sources may yet need to be proven, but I’ve noticed that as the nonnative numbers build, the native blue orchard native bees, and leafcutter bees who also may use the nesting tubes later in the season start to decline.
 

The two Japanese Hornfaced bees are the most likely mason bees to be attracted to man-made structures. As is sometimes the case for cavity nesting bees, the male is smaller, has a white face, and longer antennae.

     There’s also a much larger nonnative bee, the Giant Resin Bee (Megachile sculpturalis) that is now getting common in our area. They compete with cavity nesting bees, and I believe they will pull out or disturb the other bees’ nests when they can, nesting later than many native bees. For more about them, read this blog article I put together on them: https://capitalnaturalist.blogspot.com/2015/07/giant-resin-bees.html.

Two nonnative Giant Resin Bees fight over a nesting space. Notice one has pollen all over its scopa, or belly "hairs".

    Many other types of bees, wasps and other creatures make use of these type of nesting structures too, including mason wasps, leafcutter bees, and grass-carrying wasps.

A Grass-carrying wasp has made its nest among numerous mason bee nests.

Though it may look very similar, the smooth features make this more likely to be a mason wasp rather than mason bee.

     So do your part and become a bee rancher yourself. You’ll be amazed at the activity and the new mini ecosystem that develops around the nests, while you benefit these neat pollinators and your garden as well.                                                                                                                                     
   

Bee/Pollinator Basics

   

• Avoid using pesticides, herbicides, and fungicides when possible.
• Plant for continuous blooms throughout the season (so you have continuous food sources).
• Use mass plantings as it's easier to see a bunch of plants blooming when flying than single blooms.
• Include native host plants for caterpillars and oligolectic (specific pollen requiring) bees.
• Provide basking spots when possible.
• Consider puddling areas for butterflies and mud plots for certain bees and wasps.
• Try to locate your garden in the sunniest location you have for best bloom production.
• Consider flower color and shape (reds are the worst, blue/white/yellow open top flowers that serve as landing platforms are the best. Composite flowers supply multiple food sources per landing).
• Avoid double-flowered or other cultivars/nativars as they often sacrifice nectaries for more showy petals. 
• GO NATIVE!  As evolution provided flower colors and shapes that pollinators found attractive rather than cultivated or introduced plants that people find attractive, best not to gamble and go with non-cultivars or nativars (very few of which have ever been tested for attractiveness to pollinators rather than people). Choose native plants, its what the pollinators chose and evolved.

Picky About Pollen

      About 35% of our bees are specialists, depending on a limited range of plants (usually a genus or family) to collect pollen (though they can often nectar at many more). They cannot reproduce without the specific pollen of these plants they evolved with. They are oligolectic. If they collect pollen from a single species they are monolectic. If they use various plants they are polylectic.


Some particular pollen producing plants for specialist bees:

•  Blueberries & Deerberries (Vacciniums)- at least 5 bee pollen specialists
• Native Loosestrifes (Lysimachia) - at least 3 oil collecting bee specialists
• Hollies (Ilex)
•  Ironweeds (Vernonias) - at least 2 bee pollen specialists
• Willows (Salix) - at least 8 bee pollen specialists
• Native Thistles (Cirsium) 
• Pickerelweed (Pontederia cordata) - at least 3 pollen specialists
• Ground Cherries (Physalis) - at least 3 specialists
• Goldenrods (Solidago) - a t least 11 bee pollen specialists
• Asters (Symphyotrichum) - 8 specialists
• Aster Family - at least 131 specialist bee associations
• Rose Family - at least 102 specialist bee associations

Bee Nesting Structure Basics

• Most spring time solitary bees tend to use the same areas each year very early in the season, so try to have bee nests/structures out by early March.
• Bees, like most other insects are "cold blooded" not producing internal heat, so placing basking sites and nesting structures so they catch the morning sun but are out of the baking afternoon sun work best.
•  Bees lay female-producing eggs the deepest in the holes/tubes that they can while male-producing eggs are closest to the entrance hole. To maximize the number of reproducing females tubes/holes should be 5-8inches deep.
• While 5/16inch diameter holes are a good compromise for many bees, vary hole sizes to attract different bees and wasps. 
• For better predator and parasite protection, most bees prefer structures and tubes/holes that are sealed off in the back.
•  As most of the bees attracted are solitary, packing them close together attracts predators and parasites. Sanitary conditions of clean or new tubes/holes are best. Consider moving the colony every few years.
•  Do not move structures once they are start being actively used. Each bee remembers where its individual hole is locates, so moving them often disorients and often leads to them abandoning their nests.Make sure they don't sway or move.
•  In addition to having nearby nectar/pollen sources, mud sources are used by many bees and wasps, so maybe good to provide or have nearby.
• Provide protection form the rain and wind when possible, such as under roofs or eaves if the structure is not built with these protections in place. 
• Consider placing large screen in front of of bee structures that have openings to easily let bees through but still protect against predators. 
• Once all the holes/tubes are filled and sealed, they can be moved with no harm (perhaps to be stored in a cool garage or shed where they may be protected but  still experience cold so as to not emerge early.