Get ready for Pollinator Week: Let’s play pollination bingo!

Here in Maryland, June is the month when it starts to get hot and we start seeing fireflies, but also when a lot of plants flower and a ton of insects are flying around! Also, June is when The Pollinator Partnership has declared National Pollinator Week to happen. And finally, June is also the month when kids (and adults) start to end school and may want to have some extra distractions. So, taking all of this together, it seems to me that June is the perfect month to invite you all to join me in doing The Ultimate Pollination Bingo!

Pollinator photo gallery by Christa Carignan, University of Maryland Extension

How does it work?

1- Download the bingo card. 

2- Print it or carry it on your electronic device.

3- Find some friends and/or family, and get out there and try to do a full card! 

4- When you’re done, share it with us through our social media channels, by taking a picture of your card (and you!), tagging us @UMDHGIC and using the hashtag #PollinatorWeek.

Happy June and let’s have some fun!

Note: many of the tasks in this bingo card relate to my previous posts, so feel free to go back to them and check them out if you don’t know how to do certain things! 😊 

pollinator week - June 21-27

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,, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Apples and strawberries, or how pollinators feed us

You may have heard that pollinators are suffering and that we need to support them so they can continue to stay around us. You may also have heard that as humans, we need pollinators because if we lose them, we also will lose our ability to feed ourselves. How is this so? In this blog post, I want to take some time to think about the importance of this, visiting two examples of foods very familiar to us: apples and strawberries. Hopefully, by the end of this article, you will be sending loving thoughts to pollinators every time you take a bite of these delicious fruits. 😊

Do apple trees need pollinators?

Like for all fruits, apples form after the fertilization of the ovules present in the apple flowers (check out this blog about how this works). If pollination and then fertilization happens, we end up with juicy and large fruits, which enclose the plant’s seeds, and which can be used by the plant to disperse their seeds. For this reason, the fruit we eat will only form if there has been fertilization. Unlike other plants which can use their own pollen to form fruits, apple flowers (but also cherries, apricots, and peaches) cannot do so, and they need to have an organism actively transfer the pollen from one flower to another: a pollinator!

Pollinators of apple trees can be of many types but they are mostly bees. These insects are sometimes managed, with a large series of honeybee or mason bee colonies brought to orchards or gardens to support pollination. Many times, however, it is not the showy presence of these large managed colonies, but the quiet “hidden” activity of a multitude of solitary and wild bees who perform the pollination of these flowers. (Read here to learn about wild bees.) These pollinators are often overlooked, but it is really these little ones that save the day in most gardens.

Apple flowers are pollinated mostly by bees, which can be managed (like honeybees), or wild (like metallic bees or native bumblebees). Photo: Hugo.

Sometimes we don’t realize the value of something until we don’t have it anymore. If you have apple trees in your garden or on your farm, you may have realized that if we have a year with a cold spell when apple trees are flowering, the tree will produce very few apples. This is most times directly related to the need for pollinators that these plants have. In fact, insect pollinators have trouble moving and flying at cold temperatures, which means that if it gets cold when the apple tree flowers, pollinators will not be able to visit the flowers because they cannot reach them. If the spell lasts throughout the whole flowering time, then most of the flowers will not receive any pollen and no fruits will be formed.

Weirdly-shaped strawberries? What’s going on?

The region where I grew up in Argentina is locally known for their delicious strawberries. Every early summer, we would get these small wooden boxes with small, sweet, and incredible strawberries. We would then wash and cut them, and eventually eat them like that or (my favorite) with whipped cream. I never thought at the time that I would today be thankful to all those pollinators for creating such fond memories I can keep forever. How so?

As most plants, strawberries can partially self-pollinate, but get better pollinated if pollinators are around. Like apples, strawberries flower early in the growing season, and a cold spell during their blooming time can make them lose their pollinators, and can lead to irregular strawberries or to no fruits at all. Why is this?

Strawberry flowers are formed by a multitude of mini female organs (shown with the black arrows, on the left), which eventually become a multitude of mini-fruits (shown with the white arrows on the right). Each of these mini-fruits carries one seed and is held by a “base tissue.” The group of all these mini-fruits and the base tissue is what we call a strawberry. Photo: A. Espíndola.

In the case of strawberries, what we consider a fruit is in fact a series of tiny fruits (each little seed we see on a strawberry is one of those fruits) all growing together and in parallel on a “base tissue.” It is this whole “mega-fruit” that we call a strawberry and that we eat. As for apples, strawberries are also particularly well-pollinated by bees, and it has been shown that it is really the wild bees that we need to thank for their services here! Also, like for apples, when pollinators are not around because they are just not able to survive in the area or because they can’t move due to low temperatures, only some of these tiny fruits will get to receive pollen and be fertilized, meaning that only those parts of the “mega-fruit” will get to develop. When this happens, we obtain strawberries that are odd-shaped and that look deformed. These strawberries can still be eaten; they are just not as full and sweet as they could have been if the pollinators had been around.

I want apples and strawberries. What can I do?

We have treated in previous blogs some specific actions you can take in your own green spaces, gardens, and orchards to help pollinators thrive and continue helping us get our own delicious food. And in fact, what better way to thank them for their help in feeding us than to provide food and nesting spaces for them!

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,, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Some plants are not cool, skunk cabbage heats up

IMG_3725-eastern skunk cabbage at pine hole bogEastern skunk cabbage at pine hole bog by dreamexplorer is licensed under CC BY-NC-SA 2.0

The middle of the winter may seem like an odd moment to think about flowers. In fact, if I look out my window, I can barely see the ground, with most of it covered in snow or ice. So, flowers and all the greenery of spring and summer seem like something that happened in another world which today seems sooooo far away! There are some flowers, however, that defy some of these rules of low temperatures and do a revolution in nature (OK, maybe not a revolution, but still…). In today’s post, and although surrounded by ice and snow, I invite you to join me and warm up using the heat that some plants produce, since we’ll be talking about heat-producing plants!

Really?! Can plants produce heat?

The short answer is yes, which is super cool in itself. The long answer is yes, but let me tell you how, and what are the advantages of producing heat (and why not all plants do it).

The production of heat in plants is relatively rare, and this feature is found mostly in plants considered to have evolved a long time ago from an ancestor to most living plants. Today, heat production in plants is restricted to groups associated mostly with tropical and subtropical environments, such as water lilies, aroids, palms, and birthworts.

Unlike what we may expect, heat production in these groups has not evolved to keep the plant alive, but rather to help the plant reproduce. In these groups, heat production is associated with floral maturation and in particular to pollinator attraction. In these cases, different parts of the flowers increase their metabolism at a specific point in their development, leading to an increase of temperature that in some cases can be extremely noticeable.

In some cases, the heat has been described as a reward for pollination. (Check out this other post for other “special” rewards pollinators get from plants.) This is because it may occur at times of the year (or the day) when the environmental temperatures drop a lot, and when pollinators that visit the flower could benefit from an extra source of heat.

In other cases, heat is known to promote the release and spread of floral odors, which attracts the preferred pollinators. In many cases where heat production is present, it has been observed that plants also display a way to retain the pollinators, such as floral chambers, and in many of those cases the interaction between the plant and its pollinators involves luring and temporarily trapping the pollinators!

plants in the arum family
Some arum family plants (here, the European Arum maculatum) temporarily trap their pollinators. The species shown here displays a chamber in the lower part of its “flower” that is closed by hairs (shown on the right), which let the insects in but makes it hard for them to leave. While the flies are trapped in the chamber, the flowers mature, dropping pollen on the flies. These flies will be released after a while, and some of them will be caught again by another plant, leading to the cross-pollination of the species. Sneaky, sneaky! Photos: A. Espíndola.

While it takes a lot of energy from the plants to produce heat, this usually allows them to flower early in the season while other flowers are not around. This reduces inter-plant competition for pollinators, makes the plants easy to find by pollinators, and increases the chances of having pollen be transferred from one flower to another — all of which increases the number of seeds plants are able to produce.

Our very own heat-producing plant, the Eastern skunk cabbage

Many of you may be familiar with Eastern skunk cabbage (Symplocarpus foetidus), which is among the first plants we see peek out their leaves in the snow or the ice in the early spring. Besides being among the first plants to appear in our region, they are actually also among the first to flower, and that flowering and their pollination are intrinsically related to heat production.

Skunk cabbages belong to a mostly tropical family of plants, the arum family (Araceae). Fortunately to us, some of them do occur also in more temperate regions like ours (another native Araceae from our region is the beautiful Jack-in-the-Pulpit, Arisaema triphyllum). As with many other Araceae (for example, the titan arum), skunk cabbage attracts their pollinators through the production of a very pungent odor, which gives the plant its common name. And like all Araceae, their flowers have a very special shape that allows them to not only produce but also retain heat.

skunk cabbage
The skunk cabbage has a typical arum family flower with a bract that covers the central part of the flower. The central part displays all the reproductive parts. In the picture shown here, it is possible to see the yellow pollen exposed on the flowers of this plant. During flower maturation, the reproductive part heats up, reaching temperatures of over 20˚C (about 70 ˚F)! Center and right images show pictures of the flowers taken using a camera able to measure surface temperature, with a color scale that relates shown colors with temperatures. Photos: left: Janet and Phil; center and right: Onda et al. 2008.

When their flowers start to mature, the “head” of the flowers heats up reaching temperatures of about 70˚F (!!!), even if the surrounding temperatures are below freezing. This heating leads to the release of aromatic odor bouquets, formed mostly by compounds rich in sulfides (thus, the stinky odor). Even though this odor may not be the most attractive to us, it is very much so to the skunk cabbage’s favorite pollinators: small flies and beetles that may be lured by the flower “thinking” it is their favorite food or egg-laying site.

In defense of the plant, though, even though the attraction may be slightly dishonest, the lured pollinators may actually benefit a bit from the visit. While some of them may indeed find laying sites on the plant material, most of them will benefit from the heat received, which especially that early in the season is a much welcome reward! This heat also allows the pollinators to become more active and sometimes even mate within the plant’s flower, which also benefits their own reproduction. Finally, and most importantly for the plant, through this heat release and all the insect movement associated with it, insects passively pollinate the flowers, getting covered in pollen and later transferring it to other equally stinky and warm skunk cabbage flowers. Isn’t this super cool?… I mean, warm?

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

New! Anahí is starting an Extension Blog in Spanish! Check it out here,, and please share and spread the word to your Spanish speaking friends and colleagues in Maryland. Bienvenidos a Extensión en Español!

Hot cocoa, bugs, and forests

Last week my neighborhood hosted the traditional Christmas tree lighting event. Usually this event involves lighting the large Christmas tree across my street, having Santa come visit the kids on the firefighter truck, and sharing a cup of warm chocolate while chatting with the neighbors. This year, things were a bit different, with the lighting being live broadcasted, Santa parading the neighborhood on a truck, and chocolate being picked-up at one of our neighbor’s yard and enjoyed at home.

I have been since thinking a lot about this event, and how important it is to maintain the social ties in our neighborhood. However, I also have been thinking a lot about how the food at this event is almost as important as the event itself; how the chocolate was not left out of this year’s modified event. And this made me realize yet again how foods are central to our social ties, and how losing them would also make us a bit lonelier. So today’s post, the third in our comfort foods series, will be about that food that was so important to my neighborhood this past weekend: chocolate. Join me today in exploring how cacao comes to be, and how partnering with nature helps its (re)production.

cupcakes with chocolate sprinkles
Chocolate – the ultimate winter comfort food. Photo: Kathy Smail

What is cocoa?

The cocoa we find in the chocolate we eat and drink comes from beans of the cacao tree, a small tree in the mallow family. As for the other comfort foods we talked about in my last two posts (spices and vanilla), cacao is also not grown in the USA, and thus has to be imported. (Interestingly, it also has to be 100% imported into the countries we usually associate with chocolate, like Switzerland and Belgium.) Cacao, indeed, can only grow in very humid rainforests and can only be cultivated close to the Equator. Today, the major producers of cacao are in West Africa (e.g., Ivory Coast, Ghana) and the Americas (e.g., Ecuador, Brazil).

cacao tree a the forest
The plant of cacao, Theobroma cacao, is a small tree naturally occurring in South and Central America. The fruits of cacao plants grow directly attached to the trunk. Photo: F. and K. Starr

Even though cultivated in Africa, the cacao plant originates in South and Central America, where the species grows in the wild. Studies demonstrated that the wild plant was domesticated one or two times, first about 5,000 years ago in the Amazon, and about 3,500 years ago in Central America.

Although, as I said before, cacao beans are the central ingredient of chocolate, it is suspected that the first uses of cacao were not based on the consumption of their beans, but rather of their pulp, which is sweet and readily ferments to produce alcoholic beverages. Researchers believe that the use of beans for making the chocolate drinks the first Spaniards saw Aztec emperors drink was indeed a secondary use of the fruit.

How is cacao produced?

Unlike many of the crops we eat, most of cacao production is done by small-scale farmers. Being small trees, cacao fruits are produced in cacao orchards, usually established in areas previously occupied by rain forests. The fruits grow directly on the trunk of the tree, and need to be harvested regularly, since all fruits do not ripen at the same time. Once harvested, the fruits are cut open, and the pulp and beans are separated from the husks. While the husks are discarded, the beans are left to dry out, at which point they become dark and start looking like the little pictures we sometimes see on our chocolate bars.

cacao pod split open
The fruits of cacao are large husks that contain the beans and a sweet pulp. Note the violet/whitish color of the fresh beans, which will eventually turn brown after drying. Photo: Presidencia República Dominicana

As we see, a central part of cocoa production (and us getting the yummy chocolate we like) is the production of fruits, which seems to be defined by many aspects of the production. On the one hand, poor soils lead to yield reductions. Interestingly, cacao trees are adapted to growing in the understory of the rain forest and for this reason had been initially grown under other trees. However, once it was observed that their productivity increased if exposed to full sun, the accompanying trees started to get cut off, further contributing to the deforestation of the rain forests where they are usually grown, and increasing the monoculture of cacao plants.

After some years of higher yield, farmers realized that their trees became less and less productive, and came to understand that the presence of other trees in the orchards maintained the nutrients in the orchard’s soil, what eventually benefited fruit production. Today, in order to maintain yield and sustain the soils, cacao is recommended to be grown in what is called agroforestry systems, meaning that orchards are interplanted with other trees, which enrich the soil with nutrients, and provide a more natural shady environment in which the cacao trees can grow. The little label with a frog that we see on some certified chocolate packages indicates indeed that the farms where the cocoa used in that chocolate was produced following such environmentally friendly practices. Interestingly, as for many environmental practices, it was shown later that using agroforestry methods for cocoa production was not only beneficial to soil fertility; it also indirectly improved fruit pollination, thus improving yield through different paths!

cacao plants
Agroforestry practices allow cacao plants to grow under the canopy of larger trees. This improves the quality of the soil, promotes the presence of pollinators, and leads to higher yield. Photo: J. Rocha, from Rocha et al., 2019

How is cacao pollinated?

Why am I talking about pollination if I was just talking about planting trees? There’s a relationship, I promise! Let’s back up a bit. Unlike other crops (e.g., pecans) most cacao plants need to be cross-pollinated to produce pods and beans. This means that most cacao varieties need to receive pollen from another plant to produce fruit. In the case of cacao, the pollen cannot be transferred by wind, which makes animal pollinators central to cocoa production. In a surprising turn of events, even though we tend to think about pollinators as bees or butterflies, this wonderful fruit is mainly pollinated by a very unexpected organism: a biting midge! 🤯

cacao flower and pollinator midge
Midges of the genus Forcipomyia are the main pollinators of cocoa flowers. These tiny flies visit cocoa flowers and get covered in pollen, as seen in the picture on the left. Photos; left: S. Forbes; right: C. Quintin

Males and females of a group of midges (genus Forcipomyia) act as the main pollinators of the small cacao flowers. These midges visit the flowers to feed on nectar and pollen, which provides energy to the insects and helps females in egg production. While moving from flower to flower to feed, they transfer pollen between flowers from different trees, and increase fruit production. From this perspective, we need to thank these midges for the delicious chocolate we eat and drink!

And this is where planting trees relates to pollination. These midges prefer to develop on humid and shady environments, using leaf litter as a laying site. Making the soils shadier and increasing their leaf residues, agroforestry practices in cacao plantations directly benefit midges’ populations… and cacao production! Thus, through increasing the diversity of trees in these plantations, farmers can both make the soils provide nutrients for the plants to grow, and maintain large midge populations that ensure the effective pollination of cacao flowers. Isn’t it impressive what we can accomplish when we work with nature? And I mean, isn’t chocolate worth it?

Happy Holidays, everybody!

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

Vanilla and food: not plain when it comes to pollination

You decide to bake some cookies. You have your butter stick ready to go, you open your pantry to look for the ingredients. There is flour, oats, sugar, chocolate chips; things look good. You then realize that you’re missing that one ingredient, the one that makes it all come together: vanilla! Luckily, you can quickly buy some fresh vanilla pods or vanilla extract. In a couple hours you are there, enjoying your cookies and the pretty fall landscape.

This is all good, but have you ever thought how that spice – vanilla – gets to your pantry? And who is allowing for that to happen? In today’s blog, the second in our comfort food series (part 1 is here), we will talk about this spice that is so present in our lives that we may not even think about it. Let’s talk about vanilla and how appreciating it is tightly linked to understanding pollination and the key role of pollinators in our food system.

What is vanilla?

What we consume as vanilla is the fruit and the seeds of an orchid, the vanilla plant. This fruit comes in the form of a pod, and the tiny “dust” that comes off it is the hundreds of tiny seeds that this plant produces in each fruit. Vanilla orchids have a vine habit and in the wild are found clinging to trees in the forests of Central and South America. Considering this natural habit, all vanilla cultivation is done vertically, using different types of support.

vanilla plants
Vanilla orchids have a vine habit, and the pollination of their flowers leads to the development of the pods and the tiny seeds we consume. Photos: M. Paredes, M. Manners, Joy.

Although vanilla is now cultivated in several parts of the world, it is accepted that all cultivated varieties/species are Meso- and South American. Indeed, the plant species had been known to be selected and used by Natives of those regions prior to the arrival of Europeans in the New World, but it is only following that arrival that Europeans created a strong demand for the spice. From this respect, if we can today enjoy our yummy cookies and cakes (and more!), recognition is due to the ancient selection done by Aztecs, Totonac, and Mayas in the current Mexican territories.

vanilla vines and pods with a historical description about use
Each plant produces several pods that are harvested and dried before commercialization. Historical descriptions (here, from 1651) indicate that the plant we know today was cultivated by Natives in current Mexico, who called it “Tlilxochitl” or “black flower”. Images: Hernández (1651), Foam.

Today, vanilla is produced mostly in Madagascar, Indonesia, and Mexico, and is the second most valuable spice in the world (after saffron). Its production, however, experienced a bumpy road and still today goes through regular difficulties, which leads to extreme annual fluctuations in vanilla prices. In fact, vanilla plantations occur in regions regularly affected by extreme weather events, such as cyclones, which can destroy a whole year of production. These events lead to large variations in yield from year to year, leading to crazy changes in vanilla prices, going for example from $20/kg in 2010 to the current $350/kg.

How is vanilla produced?

Although vanilla became a European favorite quickly after it was first introduced to the continent, the production of vanilla pods remained elusive for a long time. Indeed, people realized very quickly that without active transfer of pollen to the stigma of the flower, the flowers would not develop into fruits (see how that works), and thus the much-searched-for vanilla beans would not develop at all!

In fact, after much observation of the plants in their natural habitat, people realized that their pollination required especially the visit of a group of bees restricted to the New World, the euglossines, or orchid bees. Restricted to South and Central America, these bees have strong associations with orchids, from which the males are known to collect floral scents they use for courting females (this is super fascinating, and worth a future blog post). Some species of this group of bees are currently suspected to act as pollinators of vanilla flowers in the wild. During their visits, they passively deposit pollen on the stigma of the flower, which leads to the vanilla bean development. Although these bees do pollinate, flower visits by these bees are not common, so even in regions with bee populations, fruiting rates remain relatively low.

bee approaching a vanilla flower
In their natural habitats, vanilla flowers are thought to be pollinated by beautifully metallic euglossine bees. Photo: Gil Wizen,

Adding to this, once vanilla was “discovered” by Europeans, it was introduced into a variety of colonial lands, especially to Indian Ocean islands (e.g., Madagascar, the Comoros, la Réunion) and to French Polynesia. However, and because as I said before, the pollinators of this plant are restricted to the Americas, vanilla production was not successful in those regions. Plants would flower, but the lack of pollinators would lead to virtually no pod production. This changed when a solution was found. Indeed, there had been some early attempts to develop human-based pollination methods, which were as complex as impossible to use. It was finally a slave from the Réunion Islands, Edmond Albius, who developed a simple method to pollinate the flowers by hand, helped with a stick and his own fingers. It was only after this method development that vanilla production could bloom (actually, fruit 😉) to reach its current extent.

hand pollinating a vanilla flower
Edmond Albius was the Réunion slave who revolutionized vanilla production, developing the hand-pollination method still currently used today across the globe. Photos: Antoine Roussin (1863), F. and K. Starr.

Although one may expect the techniques to have changed since the first development of this method, the vast majority of today’s global vanilla production is still hand-pollinated following Albius’ technique! In other words, the production of the second most valuable spice in the world is currently based on pollination done by hand. And this is what I wanted to stress today. We hear a lot about the importance of pollinators, but I feel that the case of vanilla is such a clear example of how important pollinators are to maintaining not just food supplies, but also global economies: take the pollinators away and you lose basically the whole vanilla bean production chain and market. Doesn’t that make you feel especially thankful for pollination and pollinators for that great flavor in your cookies?

Happy Thanksgiving to all!

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

The buzz in your seasonal latte: Who pollinates the pumpkin spices?

Wow, fall is here. When did that happen?! And because this fall comes after a tortuous year, I want to spend time doing some soul pampering. It is for this reason that, until the end of the year, I will be talking about many of the yummy foods we love and that many times help us through rough times. And to start the series, and matching the fall season, let’s talk about how the spices that create “pumpkin spice” – cinnamon, nutmeg, ginger, cloves – go around getting pollinated and reproduced.

pumpkin spice products
How do you know it’s the fall in the US? We’re surrounded by pumpkin-spice
everything! Photos: PatentingPatch, M. Mozart, J. Kramer, theimpulsiveguy.

As a general introduction to these spices, we have to realize that they all originate outside of the US, and that most of them are even today not produced in the US. This is important to mention because it is humbling to realize how much our food habits (especially those related to comfort foods) are based on foods that are imported by the US. Further, even if that may seem futile, markets for these spices have been historically and are still currently huge, with power over these markets driving major geopolitical clashes, setting the foundations of the current global distribution of wealth, and sustaining (and sometimes undermining) societies around the world.

The cinnamon bark is collected by “peeling” the tree (Photo: P. Nijenhuis). Cinnamon flowers are pollinated by many insects, but several Apis species are particularly important (Photo: D. Valke). Shown are Apis cerana and Apis dorsata visiting other flowers (Photos: Peterwchen, R. Thumboor).


The cinnamon we eat comes from the bark of cinnamon trees. This bark is either ground or consumed in strips, which are added to savory and sweet foods. Cinnamon trees originate in South Asia and are adapted to growing in wet tropical forests. Today, the most important cinnamon producer is Sri Lanka, and most of the exports go to the USA and Western Europe. Even though we do not eat the fruits of this plant, pollinators play a key role in their reproduction. Cinnamon flowers are poor “selfers,” meaning that they produce the most seeds if receiving pollen from a different flower. These flowers thus rely on insect pollinators for their reproduction (see this post for more details about how flowers function) and among the most abundant species are three Asian “cousin” species of the managed honeybee, as well as some flies.

Nutmegs are the seeds found in the fleshy fruits of the nutmeg tree (Photo: B. Vauchelle). Nutmeg flowers are very small, pollinated mostly by thrips, and through a deceit-based pollination called “mistake pollination.” (Photos from Sharma and Armstrong, 2013). White bars indicate 1mm.


The nutmeg we consume is the seed of the fragrant nutmeg tree, which originates in Indonesia. Even though currently it is cultivated heavily in Indonesia and Malaysia, it is also produced in the Caribbean. Because the food we consume is part of the fruit of this tree (there is no nut if there is no fruit), pollination of this crop is central for food production — and this is a super-fun crop to learn about!

Indeed, only some nutmeg trees bear fruit, because half of the seeds of this plant produces male trees (which produce pollen) and the other half produces female trees (which will make fruits and nutmegs). The fun pollination story doesn’t end there, though. The flowers of these plants are tiny, bloom in the night, and need pollinators to transport the pollen from the male trees to the female flowers. So who does this job? A lot of insects! Studies in the species have demonstrated that most pollination is done by tiny thrips, and probably also some beetles, flies, and maybe some bees (here you can read about pollinators other than bees).

But let’s spice up (pun intended) this story! This plant is not only pollinated by uncommon types of pollinators; it also tricks them into pollinating! In fact, the insects are interested only in male flowers, where they can collect pollen they can feed on, and they do not care about visiting female flowers, which do not offer any pollen or nectar. Thus, the strategy used by female flowers to attract pollinators is to trick them by making them assume they are actually male flowers, a strategy known as “mistake pollination”. It’s only after they entered the female flower and deposited pollen on the stigma that the insects realize their mistake.

ginger plants
Ginger plants grow from the rhizomes we consume and production is based on clonal reproduction (Photo: S. Podhuvan). Flowers are showy and small, but their pollinators are not well known (Photo: Ogniw).


The part of the plant we consume from ginger is its rhizome, meaning that one can plant the piece of ginger one buys in the store and one would grow a ginger plant! This plant species also originated from the Southeast Asian archipelago. The plant is easy to grow, and thrives in warm climates, but most of the world production is currently from India. Under production conditions, ginger is multiplied through the planting of rhizomes, meaning that most of the production is not based on seeds. For this reason, the pollination of this species was not of high production interest until only recently. Indeed, while ginger propagation is based on rhizomes, this does not allow for the use of sexual reproduction for the development of better new varieties that may be resistant to diseases or pests. Recent studies indicated that ginger is extremely hard to pollinate because pollen has a low rate of successful pollination, leading to very low seed success. Several researchers are now focusing on identifying its pollinators, so stay tuned to know more!

Cloves are the dried immature flowers of the Clove tree. Flowers are harvested right before they open and are dried to reach the product we find in our markets (Photos: Midori, A. Heijne, Peripitus).


As with most other spice plants treated here, cloves also come from a tree, which originates from the Moluccas, in Indonesia. While the plant originates in those islands, most of clove production is currently from Indonesia and Madagascar. The part of the plant consumed is the flower buds, which are harvested and then dried to produce the spice we buy. Although we consume the flowers, these plants still require seed production to reproduce, and this is central to maintaining clove production. Because the plant can self-pollinate but its genetics are improved by cross-pollination, pollinators are very important for its reproduction. Here, again, pollination is not very well known, but flies, bees, and some butterflies are suspected to play an important role in transferring pollen, as it has been observed in a closely related (but not cultivated) species.

Note: this blog post is dedicated with love to Luke Harmon, who despises Pumpkin Spice. <3

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

Why Do Pollinators Visit Flowers? Hint: It’s Not Just for Nectar and Pollen

Other than because I think they are pretty, I love looking at plants and their flowers. In fact, one of my pastimes has become figuring where and what is the reward that pollinators get out of their visits to their favorite flowers. You may be now thinking that my pastime is a bit nonsensical, since it is pretty clear that pollinators get pollen and nectar from flowers, so why bother checking? Well, actually, that is only partially true; did you know there’s a myriad of rewards that pollinators can get from their flower visits?

In today’s post I want to tell you a bit about some of those other rewards; the ones that fascinate me so much. Let’s talk about special floral pollination rewards and where you can see them in real life!

We like essential oils, some pollinators like floral oils!

The first time I heard about floral oils my mind was blown in such a way that I became obsessed with them, to the point that now a large part of my research program focuses on them. Floral oils are a reward that many types of plants offer to their favorite pollinators: oil-bees.

But don’t let me get ahead of myself! Floral oils are a special type of oil – different from essential oils – that are produced and presented to pollinators on different parts of the flowers of some plants. Independently of what exactly they look like, all these plants are visited and pollinated in a very specialized way by oil-bees. Unlike honeybees, these oil-bees are solitary and make their nests in the ground. These oils help these bees line their nests to waterproof (!!) and strengthen them. Along with that, they also mix the oils with pollen and feed that ‘pollen ball’ to their larvae.

Macropis oil bee
The whorled yellow loosestrife (left; photo: Eli Sagor) is one of Maryland’s native plants that offers floral oils to their Macropis oil-bees (right; photo: Don Harvey). Note the shiny load of oils and pollen on the hind legs of this Macropis!

Oil flowers are present all around the globe. In our region, they are represented by several species of the yellow loosetrife plant genus Lysimachia. With their floral oil rewards, these loosestrifes sustain the rare oil-bees of the genus Macropis. At the level of the country, most oil-flowers (and their specialized pollinators) are restricted to the Southern USA, where they are visited by the large bee genus Centris. Some of these plants are the wild crapemyrtle, the prairie bur, and the purple pleatleaf.

Hungry? Please, help yourself!

Along with nectar, pollen, and floral oils, food for pollinators can come in many different shapes and forms. In fact, some flowers even offer parts of their flowers to their pollinators. In cases like this, flowers develop special structures – usually around their petals – with the only function of becoming food for pollinators. Flowers providing this type of reward are usually pollinated by beetles, who can use their strong mandibles to chew on and eat the special structures.

Sweet shrubs display nutritious structures to their pollinators, small sap-feeding beetles of the family Nitidulidae. Photo: Wikipedia commons.

One of the coolest examples of the use of this type of reward is our very own sweet shrub, Calycanthus floridus. This spring flowering plant (flowering right now in Maryland!) attracts small beetles that enter the flower and stay there for quite some time. To maintain and support them while they are helping the plant reproduce, the sweet shrub flowers englobes them during parts of their flowering (this is why sometimes these flowers seem to be opening and closing throughout the day) and present small extremely nutritious structures at the base of their petals. It is on these structures that the beetles can feed on to stay strong and healthy while they are on the flowers. If you have one of these flowers in your yard, or happen to see them in one of your walks, take a second to stop and check them; you may get to meet their little beetle friends! 

Need a hand taking care of the kids? Here I am!

Some other flowers have established even more intricate relationships with their pollinators, and what they provide is not just food, but also a house! Because in these plants the offered reward is a place for the larvae of these pollinators, these interactions are called ‘nursery pollination’. Here, the pollinator visits the plants, collects pollen, and sometimes even actively places pollen on the flower tip. By doing so, the pollinator makes sure that the plant seeds develop. This is important, because their larvae will need some of them to feed on throughout their development.

yucca moth
Joshua trees (left; photo: Shawn Kinkade) are some of the most iconic plants of the US Southwest. These plants offer a brood site to their super-specialized small moth pollinators (right; photo: Judy Gallagher).

Along with this being the reward we see in a plant we love to eat (figs!), one of the most spectacular examples of the use of this reward is found in an iconic plant of the deserts of the US Southwest, the Joshua tree. Indeed, Joshua trees produce flowers that are visited by a group of moths, the Yucca moths. These moths visit the flowers, collect their pollen, and then literally push it into the flower tip to actively pollinate it. Because the moths lay eggs on the flowers, this assures that the flower develops seeds so the larvae have something to feed on. What is fascinating, though, is that these larvae never eat all the seeds, so this really is a win-win relationship between the plant and the moth.

To see how this is done, take a look at this video!

yucca moth video
Larvae of the Yucca moths feed on a Joshua tree’s seeds. To make sure that there is something for their larvae to eat, these moths actively pollinate the plants, exchanging a brood site for pollination, and in the process display some of the most fascinating behaviors one can see in pollinators. Check out the video to see it for yourself! Video: University of Nebraska-Lincoln. 

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