Planning your garden to support specialized pollinators

Looking out my window, as the ground is covered with snow and I am getting ready for another snowstorm coming tonight, it seems ironic that I have been spending many hours these days ordering seeds and planning my garden. While I am thankful that the winter brings some rest to the soil in my garden, planning this season brings me happy memories of the scents and buzzes in my yard during the growing days… which reminds me that I should also plan for my little buzzing pollinator friends when I plan what to grow this season. In today’s blog, I want to chat about how we can plan for many types of pollinators, with a special focus on planning for specialists and not just for generalist pollinators.

Specialist pollinators – never heard of them?

As we mentioned in a previous post, pollinators visit plants to feed on nectar and/or to collect pollen to feed themselves or their offspring. However, pollen is not just there for pollinators to feed on; pollen is central to plant reproduction, so plants tend to make it both attractive to pollinators but hard to digest. For this reason, and in order to be able to properly digest the pollen, pollinators are often specialized in their pollen choices. This is because being able to digest the compounds that plants add to their pollen to make them hard to eat requires some level of adaptation, which often involves a trade-off with the ability to eat anything. There are, of course, many levels of specialization, and, while many pollinators feed on many plant families, others are more specialized than that, and feed on only specific plant genera or even species! For us gardeners, this means that if we want to support many different pollinators, we need to make sure that we are also providing for those very specialized pollinators as well!

Luckily for us, the floral choices and pollen specialization is known to some extent for Maryland and Eastern USA bees (see this site to learn more). For this reason, we know that many specialized bees in our region are also rare or uncommon… another reason to try to provide resources for them!

Who are pollen specialists in our region?

Many known pollen specialist bees in our region belong to bee genera Andrena, Colletes, Osmia, and Melissodes, which have many species considered rare or uncommon in Maryland and Mid-Atlantic.

Continue reading

How do pollinators find plants and flowers?

As we know, pollinators help plants spread their pollen among flowers, and many plants do indeed need them to be able to reproduce and set seeds. We also know that by planting flowers and providing nesting habitats, we can help pollinators’ populations and thus assist with plant pollination. However, how do pollinators find plants? In this post, we will talk about that topic, which can help us become even better at helping pollinators and the plants they pollinate.

The big picture – pollinators need to be in the area

In order for pollinators to find plants, pollinators need to be present in the general region. In fact, although the vast majority of pollinators can move and travel from place to place, all of them have limitations on the distance they are able to travel. For example, hummingbirds can travel for miles (in Maryland, they are migratory), while large bees are able to travel relatively large distances for an insect (~500m-1km), and smaller insects will not be able to travel that far. This means that if, say, we lived in the middle of a very developed area with very few pollinator-friendly resources (few flowers, lots of cement, no green areas, etc.), planting a pollinator garden will attract few pollinators at first. This is due to the fact that it is likely that few pollinators are present in that area, and thus it will take a while for certain groups to arrive and establish in our garden.

It is for this reason that many communities tend to try to establish joint pollinator-friendly actions, and encourage many people in the region to participate (e.g., becoming Bee City USA-certified, creating “pollinator highways or corridors”). By increasing the regional number of pollinator-friendly resources, the whole region becomes more pollinator-diverse, and any supplementary action is more likely to improve pollinator support. As we talked about in a previous post, if you are interested in promoting pollinator-friendly habitat on your property, it may be a great idea to talk to your neighbors or your City, and see if others may also want to participate. In terms of pollinator-friendly activities, the saying “the more, the merrier” is very much true!

pollinator habitat sign in a garden
Pollinator-friendly actions are very effective when they are coordinated across regions. Photo: A. Kokai.

The local picture – different pollinators prefer different plants

As we mentioned in other posts, not all pollinators are made equal, and this is also true in terms of what plants will be found by what pollinators. For example, hummingbirds tend to visit tubular and reddish flowers, while syrphids prefer open flowers, and bees tend to visit flowers that they can access with their mouth parts (see this post to learn more). 

These floral preferences are due to the different pollinators’ abilities to see different colors, the presence of specific attractive floral scents in different plant species, and the ability of different pollinators with different body and mouth part shapes to handle and feed on flowers, and the matching of pollinator presence and flowering time. The practical consequence of this is that if we want to help many different pollinators find their preferred plants, it is necessary to grow different types of plants in our green spaces. By doing this, we would always provide resources that will be preferred to at least one pollinator, and by providing different types of resources, we can make sure that many different types of pollinators are supported by our plants. In order to do this, there are different floral mixes that exist that allow us to plant diverse floral resources appropriate for our region, which lets us build a diverse and welcoming floral bed for many pollinators.

Planting diverse floral resources will attract many different types of pollinators. Photo: C. Celley/USFWS.

The super-local picture – pollinators need to see the plant to access it

This will sound silly, but pollinators need to be able to have access to the plant to find it. For example, if a plant is not clearly displayed or hidden by many other plants or structures, it will be hard for pollinators to find it… even if the pollinator is present in the area and the plant in question is a preferred plant. This means that for us to help pollinators, we need to make sure that our plants are findable by the pollinators. Picking appropriate parts of our green spaces to plant our pollinator-friendly plants is thus key! For example, plants that require full sun to grow should be planted in those conditions and not under the shade of other plants or behind structures.

To know what these specific conditions are, there exist several resources (for example, see this useful and simple resource (PDF) published by the City of College Park, MD). These resources allow us to pick the best growing spot for our plants, making them easily findable by their pollinator friends.

Finally, pollinators are more likely to find plants if there are several of them! This is particularly true for smaller herbs, which may not display many flowers. By increasing the number of plants planted in an area we are also making the plant species more easily findable to the pollinators.

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí. Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Introducing the king of fall fruits: persimmons!

It’s fall, the air is starting to get crisp, you are walking and you see these strange trees. You are sure that they are trees, yet they have these fruits that look like tomatoes… but they are on a tree. What are those fruits? They look so attractive with that wonderful orange… should you harvest them? Should you eat them? Are they any good? What IS this? In today’s post, I want to (re)introduce you to these plants and their fruits, and hopefully the next time you see them you will have answers to all those questions and will know what to do. 😉

persimmon tree in a yard
In the fall, persimmon trees are recognized for their many orange fruits that look like tomatoes! Photo: P. Tain.

What are these orange fruits?

These fruits are what here in the USA we call persimmons (from the Powhatan word “pichamin”). Persimmons are the fruits of a group of trees that belong to the same family as ebony, and that can be found on a number of continents, including North America. Among all the persimmon species that exist, a number of them are edible, producing fruits in late fall. In the USA, there are two persimmon species that produce edible fruits, and one of them is native to right here in Maryland: the American persimmon (Diospyros virginiana).

Although the wild American persimmon still grows in our forests and was well-known by native Americans, who used its hardwood, consumed the fruits, and introduced them to the European colonists (see some Native American legends involving persimmons here), the American persimmons we see cultivated in orchards come from selected lines. Indeed, varieties of American persimmons have been selected, and many cultivars of American persimmons can be purchased and grown in gardens and orchards to produce fruit. Besides the American persimmon, there are also other species available for purchase, in particular the Oriental persimmon (D. kaki), which is very well-known in Europe.

close-up of an orange persimmon fruit in a tree
The American persimmon tree harbors fruits that turn orange, soft, and tend to fall when they are ripe. Photo: W. Pollard.

Although American and Oriental persimmons are edible both raw and cooked (see here for some recipes), it is important to note that the fruits are very astringent prior to ripening, meaning that they have to be ripe for them to be palatable. The level of ripening is usually shown by the coloration of the fruit (ripe fruits are orange), its softness (ripe fruits become soft to the touch), and their voluntary falling from the tree while not rotten. It is often said that persimmons need to go through a frost in order to ripen. This is in fact not accurate: unripe persimmons will simply rot after a frost; ripe persimmons will not rot after a frost and will in fact start slowly drying out, which will make them become sweeter. This may have led people to assume that frosts actually lead to ripening, while the frost will not help in the ripening of any fruit that was not already ripe at the moment of the frost.

Is it true that I need to plant more than one persimmon tree to have fruits?

The short answer is mostly no. American persimmon trees are what we call dioecious plants. This means that each plant will either harbor female flowers (which will become fruits) or male flowers (which will provide pollen for pollination and will not produce fruits). The first consequence of this is that if one plants or encounters a male plant, it will be impossible to ever harvest fruits from it. The second consequence of this is that a female persimmon flower needs to receive pollen from a male plant in order to produce seeds (and reproduce). In most wild forms of American persimmons, pollination is also required for fruit production.

small yellow flowers on a persimmon tree
American persimmon trees display small and delicate white flowers, which are either female or male. Photo: M. Beziat.

That being said, female plants of most selected cultivars of American persimmons can actually produce fruit without pollination. If they do not receive any pollen, these female flowers will still develop into fruits, which will not harbor any seeds and which will be fully edible. If one were to plant these cultivars in their garden or orchard, fruit production would not be restricted by female flower pollination.

But does that mean persimmons do not need pollinators?

Not really. Wild persimmons still need pollinators to transfer pollen from the male to the female plants. So who are these pollinators? In fact, we know relatively little about wild persimmon pollination. In terms of flowering time, American persimmons flower between May and June, and their flowers are small and white (and cute!). Floral visitors have not been extensively studied, but there is at least one study describing a large variety of wild bees (e.g., sweat bees, bumblebees, leaf cutter bees) visiting their flowers. From this respect, persimmons play a role in sustaining this group of pollinators and will benefit from their pollination services.

immature and adult moths that use persimmon trees for food
Persimmons also support other insects including many lovely moths from our region, such as Luna moths – top – and Regal moths – bottom). Photo: Askalotl, C. McClarren and A. Reagol, M. Clock-Rust.

Although not pollinated by them, persimmons also support other types of insects (and sometimes pollinators): moths! In fact, persimmon leaves are the favorite food of caterpillars of many native moths. In particular, Luna moth and regal moth (besides many others) caterpillars prefer persimmon leaves. It appears then that persimmons do not just feed us with their delicious fruits, but also feed many of these beautiful native moths, allowing for them to maintain their populations in our area!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí. Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Spooky Behaviors of Pollinators: The Curious Lives of Parasitic Bees

Fall is here and along with the pumpkins and falling leaves, there is one thing that pops up everywhere: Halloween! And because I can’t add Halloween decorations to a blog post, this blog will have a “conceptual” Halloween twist. Today, I want to talk about something that may seem spooky to many, but that to me showcases the stunning diversity of (pollinators’) life. In today’s post we will talk about bees that are a bit “special”: parasitic bees! Come along and marvel with me about these incredible creatures that coexist with us right here in Maryland!

Parasitic bees? What!?

Yes, you read it right. Although most of the bees we know are solitary and build and provision their nests, there are several groups that have taken an evolutionary path a bit different from their relatives. These bees have evolved parasitic behaviors, exploiting the nests and food from other bee species, and in the process actively killing the host’s brood. Because they display behaviors similar to cuckoos, birds who lay eggs in other birds’ nests and have their chicks reared by the host parents (check out this video), these bees are known as cuckoo bees.

Parasitic (right) and non-parasitic (left) bees look very different. One of the main differences is the fact that parasitic bees do not have structures to collect pollen (like hairy legs with pockets), as we can see in these photos. Photos: J. Gallagher.

Cuckoo bees look different from non-parasitic bees

Because these bees have evolved to not collect nectar or pollen for provisioning (adults do eat nectar and pollen, though), and do not build nests, they have also lost the morphological structures that allow bees to do so. Cuckoo bees thus lack all the structures commonly present in bees that collect pollen (e.g., little pockets on their legs, hairs), and all the structures that allow bees to collect materials and build nests. Unlike non-parasitic bees, who often can lay only one egg per day, cuckoo bees can lay many eggs on the same day. This adaptation allows them to take full advantage of a suddenly-available nest they can parasitize. Finally, as one can imagine, host bees are not super happy about having other bees come and exploit their nests… and they defend them! For this reason, cuckoo bees are strongly “armored”, with thick and bulky structures that can protect the parasitic females against the likely attacks from the host bees. And, last but not least, some cuckoo bees can camouflage using body odors that are similar to the host, which allows them to enter the nests without being “smelled”. Cool, heh?

But how do they do it?

A trait common to all these bees is that they have high levels of specialization on what other species they parasitize, meaning that one parasitic species will often parasitize a relatively small group of closely-related non-parasitic bees. For this reason, there are different methods cuckoo bees use to parasitize their hosts.

Larvae in many cuckoo bees are equipped with impressive mandibles that they use to attack and kill other larvae developing in the parasitized brood cell. Look at these weapons! Image: Rozen et al., 2019; American Museum Novitates.

The first main way is parasitizing brood cells that have been already closed. In this group, the females enter a foreign nest where closed cells are present, open the cell(s) where they want to lay the egg, kill the host’s egg with their sting or mandibles, then lay an egg in the (now empty) cell and close it. Other species that also parasitize closed cells are those in which the females open the cells, but instead of killing the host egg, just lay theirs in the cell before sealing it back. In this case, it is not the female but the larvae that will kill the host egg/larva. These parasitic larvae have strong mandibles that allow them to attack the resident larvae and kill them, keeping all the resources for themselves. Finally, other cuckoo species do not wait until the host cells are closed. The females of these species enter nests where cells are still open, and lay their very small and hard-to-see eggs in the open cells. The host female often oversees them and closes the cells with the parasitic egg in it. The parasitic larva develops in the closed cell and also uses its strong mandibles to attack and kill the host larva while in the cell.

Do parasitic bees exist in Maryland?

Yes! Although these life histories may seem like they are coming from another planet, we do not need to travel to exotic places to be able to encounter these species! They also occur right here!

The small Macropis cuckoo bees Epeoloides pilosula are very rare in Maryland and protected in most of their North American range. Photo: M. Veit.

A very cool species that is very likely present here in Maryland is the Macropis cuckoo bee Epeoloides pilosula, which parasitizes nests of the oil-bee of genus Macropis. Because of the level of specialization of both the oil-bee (on their host plant; see here to learn more) and its parasite, E. pilosula is very rarely encountered and is currently protected at different levels in Eastern North-America.

There are several species of Nomada or Nomad cuckoo bees in Maryland. These species often parasitize nests
of ground nesting bees. Photo: M. Lucas.

Another very neat example of local cuckoo bees are the parasites of Andrena and other mining bees: the parasitic bees of genus Nomada. The rule of lack of hairs and structures to collect provisions for the nest is very much true for this species! There are about 30 species of this genus known to be present in our state, and many of them are rare. While the spotted cuckoo bee Nomada maculata is somewhat regularly found in the state, Nomada bethunei is known only from a couple localities. Most of these Nomada species are, however, rare and often under conservation threats.

Will parasitic bees drive other bees to extinction?

Parasitic and non-parasitic bees have been co-evolving for millions of years, and it is very unlikely that this type of interaction would drive species to extinction. Indeed, the parasitized species also have evolved ways to protect their brood (something for another post). Interestingly, however, because parasitic bees are so specialized on their hosts, it is they who may be even more at risk of extinction than their hosts! Indeed, cuckoo bees are rare, hard to find, and are likely to have populations die out as soon as their host species disappears from a locality. From this respect, and if we want to protect the diversity of this super cool group of pollinators, providing resources for them and their hosts (see this and this post to learn some ways to do this) is key to maintaining the populations of these rare and fascinating parasitic bees!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Create a pollinator-friendly garden

What did you have for breakfast? 

If your plate included toast with jam, fresh berries, granola with nuts, coffee and juice, you had a nice balanced breakfast, right? Take away everything that needs a pollinator and your left with only dry toast and plain granola. That’s how dull and diminished our diets would be without pollinators.

Bees, butterflies and other pollinators are responsible for one in three bites we eat.  They are crucial to not only our food supply, but to our ecosystems. Pollinators build healthy habitat. They keep plant communities vigorous and able to reproduce naturally, supporting biodiversity and providing food, cover and nesting sites for wildlife.  

Unfortunately many pollinators are threatened by habitat loss, pesticide use, disease and changes in the way we manage the land.  They need our help.  While bees and butterflies are our pollinator poster children, we should also thank wasps, flies, moths, beetles, hummingbirds and bats for their services. 

How does pollination work?  Buzzing, flying, crawling and humming along, pollinators get dusted with pollen as they sip nectar and gather pollen from a flower.

Bee on bee balm
A bee searches for nectar and pollen in the tubular flowers of hyssop. Photo credit: Washington County Master Gardener Barb Hendershot

When they visit another flower – bam! – pollen gets transferred which triggers the formation of seeds and fruit.  That is how plants grow our food.

Without pollinators, there would be no strawberries, juicy peaches, crunchy nuts or corn on the cob.  I’m not willing to give that up.  Are you?

I didn’t think so.  So join me in helping pollinators by creating a pollinator-friendly garden.

Start with diversity. Plant many different flowering plants that bloom from spring to frost so pollinators have a constant source of pollen and nectar. Mass plants to give them a better chance of being noticed by pollinators.  Plant three coneflowers, not just one, to put out the welcome mat.  

Include native plants.  Since native plants co-evolved with native insects – including Maryland’s 400 species of native bees – they naturally support them best with better nutrition.

A silver spotted skipper butterfly explores a zinnia.
A silver spotted skipper butterfly explores a zinnia. Photo credit: Washington County Master Gardener Barb Hendershot

Think big.  Include not only annuals and perennials, but trees, shrubs and vines. Each plant type provides habitat for different pollinators’ needs from food and shelter to places to raise young.

What are some favorite plants for pollinators?  The list is long but includes columbine, phlox, purple coneflower, bee balm, butterfly weed, goldenrod and asters, redbud, ninebark, oak and birch. Here are some good resources for pollinator plants from the Xerces Society and Pollinator Partnership: and this guide on pollinator.org.

Provide habitat for nesting and egg-laying by pollinators by adding shrubs, grasses, a brush pile and orchard mason bee house.  Add water with a birdbath with a few rocks for pint-sized pollinator access. 

To really boost your yard’s pollinator appeal, limit or eliminate pesticides.  Bees, in particular, are very sensitive to chemicals.   Opt for kinder, gentler organic controls like insecticidal soap and hand-picking.

Learn more about creating a pollinator garden at our University of Maryland fact sheet. You’ll find resources for native and pollinator plants as well as tips for garden design and maintenance. 

I hope you will make your garden a pollinator hot spot, the place to be.  Or is that bee? 

Annette Cormany, horticulture educator, University of Maryland Extension – Washington County

This article was previously published by Herald-Mail Media.  

My flowers should be attracting lots of pollinators, but they’re not. What’s going on?

The presence of pollinators on flowers depends on many factors, so it is hard to know exactly why they are not visiting your flowers as much as you would expect. Plus, sometimes these factors happen simultaneously, so it may be that it is not one but the combination of factors that leads to the lower floral visits one sees. In today’s post I would like to touch on some potential reasons of why flowers may not be visited, and what we all can do to change it!

Are there really no pollinators?

We tend to think of pollinators as honeybees, and if we don’t see them we think that there are no pollinators. Pollinators come in a huge variety of types (see here to learn more!), and although you may not be attracting a lot of honeybees, you may be doing great at sustaining other pollinators!

To test if this is what is happening in your flower patch, observe carefully the flowers to see if there are other insects visiting them. Those may be pollinators too! Indeed, small wild bees, syrphids, and small beetles visit flowers often, but are usually inconspicuous. Also, make sure that you are observing your flowers when pollinators are most active, which tends to be under sunny and warm weather conditions.

Some pollinators are tiny and inconspicuous. Although seemingly not being visited, the flowers on this picture are visited by several beetles and bees. Can you see them? Photo: A. Espíndola

Pollinators have not yet had time to find your flowers

Especially if your flower patch is in an area or neighborhood where there aren’t many flowers, the pollinators in your area will need a bit of time to know that the flowers are there! It’s like when a new shop opens and it takes a while for people to know it exists. If you continue to have flowers there over the season and years, pollinators are going to start coming more regularly and you should see an increase over time.

Not sufficient(ly diverse) flowers

If you indeed live in a region where there are not many floral resources available for pollinators, you can plant more (diverse) flowers next year and/or talk to your neighbors and have them plant flowers too! The more flowers in a region/neighborhood, the more pollinators you may end up attracting overall! On this, consider talking to your City leadership and inquire on whether they would be interested in supporting pollinators by becoming a certified Bee City USA city.

Flower beds and gardens with many plant species are ideal to increase the number of pollinators in our green spaces. Photo: J. Dean

Lots of flowers but not many places to nest

Even though most pollinators can fly to get to floral resources, their flight ability depends on the species. Some species can fly some miles, while others forage just close to their nests. To make sure that there is a lot of pollinator diversity in your flower patch, you can create conditions that favor the nesting of those species that can’t travel far. For this, a great thing to do is create nest-friendly spaces on your property. One can also establish practices that ensure that critical pollinator developmental stages (e.g., overwintering stages, larval development) also have sufficient resources. This can be done, for instance, by leaving leaf litter on the ground over winter and protecting overwintering spaces (check this other post to learn more).

Some pollinators are territorial

Some pollinators (e.g., some bumblebees, honeybees, large carpenter bees, wool carder bees) can “push out” other smaller pollinators, especially while the males are looking for a mate. If the large ones are very abundant, it could be possible that they are chasing away the small ones. This would not explain an absolute lack of pollinators, but would be able to explain certain drops in abundances at certain times of the year.

Pesticide drift

Pesticide drift is a big problem for the protection of beneficial arthropods, and can lead to pollinator (and other beneficial insects) death. Drift happens when a region in the vicinity of your property is treated with pesticides, and the products drift into your property. This is really problematic when the applications are done at the wrong times, with the wrong concentrations, or using the wrong means. In particular, this can be a problem when homeowners decide to perform whole-yard spraying to control mosquitoes, which is not recommended (an exception to this are controlled community-wide sprays occasionally done by the State Department of Agriculture if disease spread –e.g., West Nile Virus — is a concern).

Unless there are strong reasons for pesticides to be continuously applied in the vicinity of your property (e.g., major and sustained outbreak of mosquito populations), this is normally restrained in time. If there has been drift, you would be seeing a drop in pollinators compared to a previous time in the year (say, the week prior to the potential drift event). If drift has actually happened, but is not happening anymore, one would expect to see the populations of your pollinators increase with time, since new pollinators could be attracted from other surrounding areas. If you suspect that drift is an issue, you can discuss with your neighbors and see if the applications are really necessary, if they are done at the proper times (ideally in the night or when beneficial insects are not active) and/or get them in touch with your UMD Extension officers, who can recommend whether treatment is even needed, and if so, how to do it. You can send your question online to Ask Extension.

If not properly done, pesticide applications can lead to pesticide drift to neighboring areas and pesticide runoff to our watersheds. Always carefully read the labels appearing on pesticide containers, and consult your Extension agents if you want to make sure to do a safe application. Image: C. Rusconi

Just a less-active year

If you have been successful in the past, it could just be that this year there is just a smaller population of pollinators in the area when your flowers are growing. For example, maybe the warm winter did not help some pollinators properly overwinter, or some disease outbreak locally affected pollinators in your area. If next year you realize that this was indeed a one-year thing, this will then be easily explained by natural fluctuations in pollinator populations.

Think broadly and don’t give up!

Remember that sometimes it is not one but the combined effect of these factors that makes that pollinator abundances drop in our gardens. If you’re not sure what the actual reason may be, your best call is trying to implement as many of the actions as you can, so at least you can exclude some variables. Either way, remember that your actions are likely not going to bring results from one day to the next, but rather from one season to the next! For example, many pollinators reproduce only once per year, so you may have to wait until the next generation (the following year) to see a difference. So, don’t give up if you don’t see an effect right away! You’re likely doing the right thing; you just need to wait a bit longer to see the result!


By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Climate change impacts on pollinators and pollination

Do you agree that the weather has been getting a bit crazy? Summers are getting extreme, some being dry, others overly wet and too hot, the winters too warm, hurricanes and tornadoes becoming more common and stronger. Climate change is here, but what does it mean? Does it even matter? In this post I want to spend some time talking about why these strong changes in our climate do not just affect us, but mostly organisms that help us survive, like our beloved pollinators and the plants with which they interact.

What is climate change?

Climate change is any change in the mean and/or the variability of the climate, which persists for an extended period (decades or longer). This means that when we hear about climate change, people can be referring to any long-term change that has been detected in the records of temperature and precipitation, as well as the variations in their extremes and averages over time. Although we tend to think about the current climate change as increases in temperature, temperature is just one aspect of it. Often, it is also the precipitation patterns that are affected, leading to extreme rainfalls or droughts. Climate change is not just a climatic curiosity; because all the places and environments we live in and obtain our foods and livelihoods from are affected by climate, changes in climate affect our lives and those of other organisms with which we coexist.

How does climate change affect pollinators and pollination?

Like all organisms, plants and pollinators are only able to survive under specific climatic conditions. If the conditions change, their options are adapting to the new conditions, migrating to regions where their optimal conditions are still present, or going extinct.

Evolving and adapting to the new and fast-evolving climatic conditions has not been often observed in the case of pollination interactions. Most species are either observed to display what is called plasticity and use their already-evolved ability to adjust to different conditions. This allows them to tolerate more extreme conditions with possibly a small loss in their ability to obtain food, grow, or mate. In the USA, it was shown that some species of bees can advance their emergence time when the winters are warmer, and match to some extent the advancing in the flowering season associated with warmer winters or early springs.

Orange-legged Furrow Bee
The Orange-legged Furrow Bee (Halictus rubicundus) is a species that has been shown to be advancing its time of emergence with increasing temperatures. Photo: M.L. Legrand.

Most species, however, respond to these changes in the climatic conditions by dispersing to new regions, where their preferred conditions are still present. For example, species from Maryland, may disperse further north under a warming climate. Likewise, species that live on the slopes of mountains may disperse upwards, to higher altitudes. However, this is often impossible, when, for example, northern latitudes do not offer the right habitat (e.g., the preferred plants are not available or there is no more natural habitat left due to human pressure), when it is impossible to disperse further to the poles (e.g., for cold-adapted species), or when it is impossible to move higher on a mountain (e.g., for alpine species). These species see their ranges become smaller and smaller, until their population becomes too small to avoid extinction.

various species of butterflies
Some species, like the Giant Swallowtail and the White-M and Red-banded Hairstreaks, have been expanding their ranges northward (top row, left to right). Others, like the cold-adapted Atlantis Fritillary or the Arctic Skipper are likely to become at least locally extinct (bottom row, left to right). Photos: T. Eagle, S. McCann, G. Lasley, S. Elliott, S. King.

Finally, other species are unable to disperse at all, because they may not be mobile or because they move too slowly for the pace of climate change. Although only through modelling approaches, studies suggest that this may be the fate of many mid-Atlantic bumblebee species like the Perplexing or the Golden Northern bumblebees, which may become slowly doomed to extinction.

bumblebees
Perplexing and Golden Northern Bumblebees have been predicted to become unable to track their preferred climatic conditions under many climate change scenarios. Photos: P. Pieluszyński, Molanic.

Climate change and extreme weather events however, also can affect the survival of pollination interactions, and not only of individual species. For example, species that are specialized on their floral preferences or their pollinators may be unable to survive climate change. If the winter is warmer than usual, certain plants and insects may start emerging and developing earlier than usual. If these advances in their developments do not match between the plant and the pollinator, the partners will not co-exist, which can have drastic consequences such as loss of food, nesting sites, or lack of seed production for lack of cross-pollination. This is one of the reasons why the Baltimore Checkerspot, Maryland’s state insect, is at such high risk from warming winters and is currently endangered in the state.

Baltimore Checkerspot caterpillar and adult butterfly
If there are warm spells during the winter, the Baltimore Checkerspot’s larvae leave their “winter sleep” too early, when their plant food is still unavailable to them, and are at high risk of dying from starvation. Photos: WikiCommons, S. Snyder.

Another way these changes in climate can affect pollination is through changes in the functioning of the interacting species. For instance, it has been recently shown that extreme rainfalls and heat are able to affect the quality and composition of nectar and pollen, the odor compounds present in flowers, and the ability of insects to move and reach the flowers for reward collection. This means that even if species were to still co-occur, these extreme climate events can affect their ability to encounter each other, which again, leads to their survival being harmed!

This is complicated! Can I do anything to help?

It’s true! Understanding all biological interactions and protecting species IS complex, but that doesn’t mean that there’s nothing one can do to help! Some ways to support pollination include providing a lot of resources for both the plants and the pollinators to survive. For example, planting many different native species and providing nesting resources in our green spaces supports pollinators that may be migrating to new areas, or ones that may be just under a lot of climatic stress.

Also, it has been thoroughly demonstrated that increased concentrations of carbon in our atmosphere are leading to the climate change patterns we are observing. The good news (if we react quickly) is that we may still be able to do something to revert it, and this does not have to be anything that affects our ability to survive. Even relatively simple behavioral changes like turning off unused lights at home, bringing the thermostat even 4 degrees higher in the summer, or reducing meat consumption make a huge difference in our carbon footprints.

If you would like to start helping pollinators by reducing your carbon footprint, I strongly recommend visiting this website to receive “personalized” free recommendations to successfully reduce your carbon footprints through simple (and also more complex) and very feasible actions. And if you would like to learn more, I also strongly recommend the webinar series by University of Maryland Professor Dr. Sara Via.

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!