Author:Anahi

A Little-Known Group of Pollinators: Beetles!

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As we mentioned in previous posts, when we think about pollinators, we tend to think of butterflies and bees, but rarely about the super important hoverflies or other groups of organisms. In today’s post, I want to tell you about another of those little-known pollinator groups; let’s talk about beetles that act as pollinators!

Beetles: “hard-shelled” pollinators

From a taxonomic perspective, beetles are a group of insects that belong to the Order Coleoptera. Among other important characteristics, they are recognized by their extremely well-protected body, in particular by structures called “elytra”, which provide a very hard cover to their wings (the wings are placed under the elytra). Generally, beetles have mouth parts that are adapted to chewing, which means that they have large mandibles that allow them to break their food. You may be wondering why I am talking about these structures in a pollination post… well, as for all pollinators, the shape and function of a pollinator define what they do (and don’t do). Let’s see how this affects our pollinating beetles.

a black and yellow beetle on a purple flower
Beetles are common flower visitors, with some of them being very effective pollinators. Because of their very well-protected bodies (see elytra covering the “back” of this beetle), they often spend a lot of time on flowers, where they feed on pollen, nectar, and floral parts. In this picture, we can see a cetoin scarab beetle with prominent elytra and a very hairy body that helps them transport pollen grains between flowers. Photo: C. J. Sharp (CC).

In the case of beetles, the fact that they are well protected by those elytra makes them more “confident.” That “hard shell” provides a great deal of protection against predation by other arthropods, which in turn makes them generally more “chill” in their visits to flowers. Unlike butterflies, bees, or hoverflies, beetles tend to move little within and between flowers, taking all their time to get the resources they need from them. For this reason, they are often considered as more generalist and inconsistent pollinators than their less-protected counterparts.

The shape of their mouths and their feeding habits also affect their efficiency as pollinators. In fact, beetle visits to flowers tend to be relatively destructive because they are attracted to them by their floral tissues, including in some cases pollen and the ovaries! In this respect, beetles tend to visit flowers to feed on them, which in some cases can lead to floral destruction. So, given this, are beetles good pollinators or just flower herbivores?

Beetles as pollinators

Among all the many different groups of beetles, some of them are considered to be particularly good pollinators. Specifically, these belong to the beetle families known as soldier (family Cantharidae) and longhorn (family Cerambycidae) beetles, families that depend on floral resources for their survival at least at one stage of their development. Other families such as scarabs can also be strongly associated with flowers for their survival. In all these groups, the beetles in question have clear adaptations that make them good agents of pollen transfer. For example, we observe different parts of their bodies covered with abundant hairs. This improves pollen transport and thus increases their ability to effectively cross-pollinate the flowers they visit.

a beetle with pollen grains on its head
Beetles that are good at transporting pollen have hairier bodies that can carry pollen grains, like this cantharid beetle that got its face covered in pollen while visiting these flowers. Note the yellow “powder” – pollen – that covers part of the beetle body and take a look at the large mandibles the beetle uses to feed on floral parts. Photo: J. Tann (CC).

Further, although these beetles tend to still feed on floral parts, they are usually much less destructive than their more generalist cousins. They often feed on specific flower parts (instead of on all the floral sections), leaving the central reproductive structures (e.g., the ovaries) intact, and thus allowing plant reproduction. These beetles are also often more specialized in their floral choices, preferring a small range of plant groups (usually one or a few species within the same plant genus), and moving more readily between flowers. Combined, all of this means these beetles can not only carry a lot of pollen (they are hairy) but also move it from flower to flower more effectively and do not destroy completely the flowers they visit.

A cool beetle pollination example

Beetle pollination is a very understudied topic in temperate regions such as Maryland, and we are still learning a lot about it. It is thus not surprising that the number of examples from our region is not super high. Let’s talk about one of them that happens to be relatively well-studied elsewhere but that also occurs in North America.

yellow and black soldier beetle on a magnolia flower
Beetles are considered some of the most important pollinators of species of the genus Magnolia. Here, a long-horned (Cerambycid) beetle on a Magnolia grandiflora flower. Photo: D. Hill (CC).

An example of beetle pollination of native plants that are also present in our region is that of Magnolia flowers. Although most of our knowledge on the pollination of this plant genus comes from studies done on species outside of North America, there are a couple of reports of floral visitors in several of our local species. From elsewhere, we know that these trees display flowers that appear to be particularly attractive to beetles: they are white, easily accessible, offer a lot of pollen, are fragrant, and in some cases even produce heat! In many of these species, the flowers appear to attract scarab beetles, which, once landed on the flowers, feed on the petals, mate, and then actively move between flowers and cross-pollinate. In North America, some studies like this one and this other one (in PDF) have found a wide variety of beetles attracted to our native species. Many of these beetles are very small and visit Magnolia flowers to feed on them, mate, and spend the night protected within the flowers.

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!

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How Do We Study Pollination?

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Pollination is such a buzzword right now, and a lot is said about pollination and pollinators. However, how do people learn about pollination and pollinators? How do people know who the pollinators are and how pollination works? Because I happen to do research on pollination, I wanted to use this opportunity to share with you some insights into how pollination is studied, what it teaches us about plants and their reproduction, and how this connects with the things we hear about pollination.

What are we studying when we study pollination?

As we mentioned in previous posts, pollination is basically how plants reproduce. Generally, pollination involves the deposition of pollen grains on the female organs of a plant, which in many cases leads to ovule fertilization and often the production of seeds and sometimes fruits. So, when we study pollination, what we are studying is the reproductive strategies of plants. If we think about plants and the many different ways they have to reproduce, it may be simple to imagine all the different aspects one can try to understand about pollination. Here I will present a couple.

The reproductive strategy of plants – selfing, crossing, or both?

Unlike us humans, many plants can self-pollinate. This means that the species that can do this can technically accept pollen from their own flower and use it to fertilize their own ovules. The consequence of this is that plants that can self-pollinate do not necessarily need pollen from another individual to produce offspring. This may seem like a nerdy technicality of mine, but the ability or not of a plant to self can have a lot of wide-ranging consequences. From an evolutionary perspective, this can affect the genetic diversity in a species or group of species, which can define whether a species can adapt or not to certain conditions, among other things. This can also have consequences for food production and plant breeding; if a plant cannot self, several stocks need to be present in a field for it to be able to produce fruit. This for example happens to some varieties of cherries, where more than one tree needs to be planted in an orchard for the plants to produce fruit.

reproductive parts of flowers
To test for plant reproductive strategies, researchers can perform controlled crossing experiments, which follow generally what is presented in this figure. Image: University of Waikato.

To understand whether a plant species can self, a basic experiment can be done. In this experiment, one creates groups of plants of the same species that will be pollinated following different methods. By comparing the number of seeds produced by each method, one can infer how the plant reproduces. In its simplest forms, one of these experimental groups of plants is manually selfed, which usually involves removing all anthers from a flower and then manually depositing pollen from the same plant on its stigma. In another group, plants are crossed using pollen from another plant. The flowers and potentially fruits of both groups of plants are then left to develop, and once fruit/seed maturity is reached, one counts the number of fruits and seeds per group of plants. If the two groups present significantly different numbers of fruits or seeds, then we can infer whether the plant is able or not to self.

Who pollinates a plant?

Imagine that we figured that a plant requires cross-pollination. Now, a question we may want to ask is how the pollen of one flower can get to the stigma of another flower. Again, this is not just a biologist niche question; this has practical and evolutionary consequences. For example, if a plant is wind or water-pollinated, it will be able to produce offspring in the absence of animal pollinators. Alternatively, if a plant needs animal pollinators, then their absence can lead to the plant’s inability to sustain its population over time. In a food production world, plants that need animal pollinators will benefit from the presence of those pollinators, leading to higher fruit or crop production when more pollinators are present (this is the case of, for example, almonds and strawberries).

To study this, scientists have a large palette of methods. Here are some. One of them involves observation of the flowers in question. For example, one can assume that a flower that produces nectar or that has special color markings aimed at directing pollinators when they visit a flower will be more likely pollinated by animal pollinators than one that does not offer any floral rewards in exchange for flower visitation. Similarly, the general floral shape gives clues about how it may be pollinated. Flowers pollinated by animals tend to have specific shapes that improve pollen deposition by animal visits, while those pollinated by abiotic factors are usually droopy or displayed in very humid areas.

markings on flowers only visible with UV light
Flowers that can look “plain” to us may have special colorations that only pollinators can see, like this black-eyed Susan, which shows its floral markings that can be seen only under UV light (a wavelength many insects can see). Observing markings or “signs” on flowers indicates that the plant may use animals for pollen dispersal and transfer. Photo: A. Davidhazy.

As said before, observations are a huge part of studying pollination and the identity of pollinators of a plant. This generally also entails spending hours upon hours over several seasons carefully observing and sometimes capturing any floral visitor and potential pollinator of a plant population. This requires patience and focus, and careful recording of the abundance, frequency, and identity of any flower visitor. This also often requires hours of identification of captured floral visitors, often under the microscope (given that most floral visitors are often insects), and through the use of taxonomic keys or the consultation of experts of specific taxonomic groups.

a man in a field using an insect sweep net
One way to understand what pollinates a plant involves hours of focused observation of flowers and capture of the animals seen visiting them. Photo: A. Espíndola.
fluroescent dyes are used to track movement of pollen by pollinators
Fluorescent dyes can be used to track the movement of pollinators and the potential for pollen transfer. Photo: Huais et al., 2022.

Along with these hours of observing and describing what is being seen, other more “manipulative” approaches exist. For example, many scientists try to understand who visits a flower by marking flowers with powdery dyes and then seeing if any animal seen visiting the flowers becomes colored with the dyes. More “technological” approaches use high-resolution cameras and artificial intelligence (AI) methods, as well as DNA sequencing to identify the presence and species identity of pollen grains on animals seen or suspected of visiting flowers.

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!

Make Your Garden Shine Like Gold This Spring With Golden Ragwort

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The golden leaves of the trees outside my window remind me that the growing season is almost over and that winter is coming. However, those same gold colors also remind me that spring is not that far away and at my place, it will start with some gold showing up in my garden. This golden treasure connects the gold of the fall with the gold of spring to close the season’s circle. Let me tell you about what I think is an underrated plant from right here: the golden ragwort!

Golden ragwort – a treasure for our gardens

The golden ragwort (Packera aurea) is a perennial native plant of our region that belongs to the sunflower family, Asteraceae. The species is found pretty much across the whole state and is commonly found in eastern North America. Its name comes from the abundant yellow flowers it produces early in the season (all that gold!), at a time when most other spring plants have not flowered. In fact, in our region, the golden ragwort starts flowering as early as March and continues doing so for several weeks/months afterward.

A species in the Asteraceae family, the golden ragworts displays many inflorescences that are of strong yellow. Photo: B. Gratwicke (CC).

Besides it being a great addition to any space that needs some floral resources, another benefit of this species is its tolerance of a wide variety of growing conditions. Golden ragworts can be grown in conditions ranging from full sun to shade, tolerate heat well, and require some soil moisture. Once established, the plants are great ground covers since they can spread easily thanks to their rhizomes.

After flowering, the rosettes and rhizomes continue to cover and occupy the ground, making them also a great resource to retain water and soil in spaces that may be prone to soil erosion. Related to this, another benefit of this strong ground cover is that because they are so good at establishing, this species can have a high potential for competing against invasive plants that we may want to prevent from arriving or to remove from our green spaces.

Golden ragworts are great ground covers, forming mats that flower for several weeks. Photo: D. McGrady (CC).

And if your green space is like mine, and often visited by deer, this is a plant for you! In fact, because plants cannot escape predation like animals, they have evolved other ways of protecting themselves against herbivores. It turns out that all plants produce chemical compounds that act as chemical shields against herbivory. These compounds can make them toxic or unpalatable to many animals, thus leading to at least an unpleasant and at worst a deadly experience if ingested. Well, it turns out that Packera aurea has some of these defenses! This means that it may not be a great idea to try to eat this plant yourself (in case you were thinking of it 😊), and second, that other mammals such as deer will not feed on it due to its toxicity… making it deer resistant!

What do pollinators think of this plant?

Because they flower so early in the season, golden ragworts are very valuable for pollinators. In fact, because there are often not too many floral resources available in the early spring, early-flowering plants such as this one play a key role in supporting early-emerging pollinators.

Packera aurea flowers have been shown to support a large diversity of bees and hoverflies, and of course, this diversity increases with the progression of the season. Among some of the species it supports are several sweat bees, little carpenter bees of the genus Ceratina, and many species of hoverflies. Interestingly, this species has also been described as one of the preferred pollen sources of the rare pollen specialist mining bee Andrena gardineri.

At the end of the flowering time, the plants create a nice ground cover with their rosettes. Photo: M. Heberling (CC).

When is the best time to plant golden ragwort?

Although the ideal time to plant it is in the early spring, depending on where you are in the state, you may be able to have just enough time to establish it this fall. Either way, the plant gets established very quickly, so if you are afraid of it being too late right now to try it, keep it in mind for the spring and check out your local native plant nursery to get your starts in time! I promise you will not regret it, and you will be thankful every spring for the lovely botanical chest of gold that will enrich your garden.

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!

Want Flowers Next Year? Here Are Some Pollinator-friendly Plants to Plant This Fall

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Although the end of the summer/early fall may seem like an odd time to think about planting, don’t be fooled! This is actually prime time to allow plants to establish and grow strong for next spring. In fact, planting in the early fall gives time for plants to establish their root system, acclimate to the new conditions, and be ready to grow as soon as the spring conditions become ideal for them to develop. In today’s post, I want to present a couple of very neat plants that can be planted now to bloom and provide resources for next spring’s pollinators. And because these are some plants that are just close to my heart, let me try to convince you to add some (or all! 😊) of these to your green spaces, so you can enjoy them next year. Let’s talk about mountain mints, beardtongues, and Culver’s roots.

Narrow-leaved Mountain Mint – Pycnanthemum tenuifolium

As its name may let you infer, this is a plant that belongs to the mint family (Lamiaceae) and, as a mint, it is very aromatic. The genus is native and restricted only to northern North America, and we are lucky to count several species within Maryland’s native flora. As is the case for most Lamiaceae, mountain mints do not only present beautiful flowers; they have been used traditionally as a food seasoning and in medicinal teas to treat colds, coughs, and fever by many Native American tribes. Although some species are currently protected in the state, some are common, one of which being the narrow-leaved mountain mint (P. tenuifolium) I want to introduce you to.

white flowers of mountain mint with a butterfly visiting for nectar
(Left) The plant establishes very well in sunny areas where it displays its clusters of white flowers. Photo: SB_Johnny (CC). (Right) The delicate flowers of the mountain mint attract a very large diversity of pollinators, such as this Pearl Crescent butterfly. Photo: S. Cadwell (CC)

This plant is a favorite of mine because it is relatively tall (~ 3-4ft), makes a lot of flowers, attracts a bunch of insects, and tolerates conditions that many other plants don’t like. As is the case for all mountain mints, the flowers of this plant are clustered, and in this species, the flowers are white and bloom in the summer. The plants attract a very large variety of insects and for that reason are one of the recommended plants by the Xerces Society for supporting pollinators in our area. Bees of all sizes, beetles, butterflies, wasps, flies, and hoverflies… nobody can resist this beauty! And to top it all, this plant grows great in full sun and even in relatively dry conditions, which makes it a great one to plant close to roads or in those areas of our green spaces where other more water-needy plants may not do so great.

Hairy Beardtongue – Penstemon hirsutus

I have to say that I have a weakness for Penstemons specifically and plants of the whole family they belong to (the figwort family; Scrophulariaceae) generally. Their complex flowers always get to me, and plants of the genus Penstemon are to me one of those that I can look at and marvel at forever. So, this is one of the first ones I want to grow every time I can… maybe I’ll convince you to plant it too?

The genus Penstemon is almost restricted to North America, where they represent one of the largest groups of native plants on the continent. They are characterized by having tubular flowers, and their coloration varies by species, going from white, to pink, purple, red, and blue. Although there are a few species native to Maryland, and several can be grown, I want to talk a bit about the hairy beardtongue, P. hirsutus (but also check out the foxglove beartongue, P. digitalis!).

pink-lavender flowers of hairy beardtongue
lavender flower with a bee
(Left) Hairy beardtongue plants display a large number of tubular flowers. Photo: K. Woods (CC). (Right) The tubular flowers of hairy beardtongue provide nectar and pollen to a variety of pollinators, such as bumblebees, other bees, hoverflies, and butterflies. Photo: A. Espíndola

The flowers of this species are multicolored, with purple tubes tipped with yellow and white. The flowers are visited by bees (including bumblebees), hummingbirds, and butterflies, and have been described to support the adults of the Baltimore checkerspot, our state insect! The plant itself is not overly tall (~2-3ft) and makes a lot of flowers. They prefer drier conditions and full sun to some shade and will bloom in the late spring/early summer.

Culver’s Root – Veronicastrum virginicum

I feel that plants with small white flowers (like this one) are often kind of forgotten, to the benefit of showier and more colorful flowers. However, Culver’s root is a little gem native to our region that any local interested in supporting pollinators should consider having around.

Belonging to the Plantain family (Plantaginaceae), the genus counts only a couple of species, one of which is the only North American native: Culver’s root (V. virginicum). Like all members of the genus, this species presents its white flowers arranged in long spikes. This species will become taller over the years, reaching 4-5 feet at full maturity. They prefer sunny to shadier spots, where sufficient moisture is present (e.g., wood edges).

The flowers mature sequentially, and because there are so many flowers in their long spikes, a single plant is likely to flower for weeks. Besides its sustained floral display, this plant is super interesting and important for pollinators because it happens to flower at a time when few other plants flower in our region (July-August). Their white flowers attract and provide food for bees, butterflies, wasps, and (hover)flies.

spiky white flowers of culver's root
Once established, Culver’s root can reach 4-5 feet in height, displaying their long spikes of white flowers. Photo: E. Enking (CC)
close up view of culver's root flower spike
A tiny bee collects pollen on Culver’s root (can you spot it?). Note the multitude of flowers present on the long spikes. Photo: A. Espíndola

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!

How Are Aquatic Plants Pollinated?

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When we think about pollination, we tend to only think about terrestrial plants. However, a large number of plants are not and actually live fully or partially in the water. These plants also need to reproduce, and thus need to have their flowers pollinated to produce seed. How do they do it? In today’s post, I will try to give a (short) answer to that question, using some native plants as examples.

You may recall from previous posts, that flowering plants require pollination to be able to produce seeds and thus reproduce. Since we are terrestrial organisms ourselves, we tend to be more aware of other organisms and processes that share that trait with us, and pollination is no exception. However, there are lots of flowering plants that are completely or partially aquatic, and these plants also require pollination to produce seeds. Depending on the specific requirements of the plants in question, some of them may use different strategies for pollination.

Wind pollination

Many aquatic or semi-aquatic plants depend on wind to transfer pollen to the female reproductive structures. Especially under conditions distant from land, using wind as a means of pollen dispersal can be extremely advantageous. In fact, being distant from land tends to reduce the types and number of animals that can visit the flowers of aquatic plants. By depending more heavily on wind, these plants usually display light and abundant pollen that can be readily blown away and potentially deposited on the stigma of the female counterparts. A global evaluation of this indicated that about a third of all aquatic plants in the world are wind-pollinated.

small leaves on the surface of water - watershield plants
a red flower protruding from the surface of the water
Watershields are very common wind-pollinated aquatics from our region. These plants display their small flowers well above water, first exposing their stigmas and the next day releasing pollen into the air. Photos: S. Elliott, S. Osborne (CC)

In Maryland, an aquatic plant known to be wind-pollinated are watershields (Brasenia schreberi). This plant has non-showy flowers that display both anthers and stigmas. In order for the plant to promote cross-pollination (i.e., avoid receiving pollen from its own flowers), the flowers of these plants go through a complex blooming process that spans two days. This process involves on the first day the receptivity of the stigma (the female part that receives the pollen) and on the second day the maturation and release of the pollen grains. When the grains mature, they are swept by the wind and can reach stigmas from other flowers that are at that point going through their first flowering maturation step.

Animal pollination

It has been shown that a large number of aquatic plants are at least partially pollinated by insects or other animals. In fact, as is also the case in terrestrial plants, aquatic plants can sometimes use both wind and animals to transfer pollen, increasing the chances of some pollen eventually reaching the stigma. Animal-pollinated aquatic plants are pollinated by a large variety of organisms, but their identity will depend on the specific place where the plant is growing and the ability of the pollinator to reach the plant and even survive in that environment. For example, while large bees may be able to fly further away from land, smaller insects may mostly visit plants that are close to land.

a closeup of the flower of arrow arum - its yellow inside
the leaves of arrow arum plants are pointed like arrows
a tiny fly with red eyes is the pollinator of arrow arum
The arrow arum or tuckahoe is an aquatic native that displays a nursery pollination system in association with small flies. Photos: Sheri, N. DeBarros (CC), K. Shulz (CC)

A special case of insect pollination of a Maryland native is that of the arrow arum or tuckahoe (Peltandra virginica). The species belongs to the Araceae family and displays a stunning pollination system. As is often the case in this family of plants (see also the skunk cabbage example we talked about in a previous post), the maturation of the female and male flowers is linked to the production of specific aromas. In the case of the arrow arum, these smells attract small flies, and in particular individuals of Elachiptera formosa. These flies seek the flowers to mate, feed on pollen, and eventually lay eggs on the plant, making this an example of what is called nursery pollination (the plant receives a pollination service in exchange for providing a brood site for the pollinator). By moving along the flower, these tiny flies move pollen from the anthers to the stigmas. Some of this pollen may come from the same plant, but other pollen may come from a different flower already visited by the flies.

Water pollination

Finally, many aquatic plants display flowers that are either completely submerged or floating on the surface of water. These plants usually use water currents to disperse their pollen. As with wind, this dispersal is very inaccurate, which usually leads to the release of a large amount of pollen. These plants have either pollen that floats on water or remains attached to the anthers which float to the stigma.

aquatic plants with tiny white flowers on the surface of water
The American pondweed is one of our native species that uses water as their means of pollen dispersal. Note the very small white flowers that are placed on the surface of water. Photo: C. Fisher

A very common native from Maryland that displays this type of pollination is the pond- or waterweed (Elodea canadensis). This species native to North America displays flowers that have either anthers or pistils, but not both. The flowers with anthers are often displayed over the water, from where they release the pollen, which lands and then travels on its surface. By moving on the surface of the water, the pollen can reach the slightly submerged stigmas of the pistilate (female) flowers, which are held on flowers that float at the very surface of the water. Because such a dispersal can lead to large pollen loss, pollen release in this species is only done when the wind is light and the water current is low. This promotes a more “controlled” dispersal and increases the chances of the pollen effectively reaching the stigmas.

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!

And the Pollinator Prize Goes to… Hoverflies!

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We hear a lot about pollinators these days, but most of the attention appears to always go to one group of them: bees. However, the diversity of pollinators expands way beyond this one group of insects, as we discussed in a previous post. In today’s post, I want to bring the spotlight to one of those non-bee pollinators, which I always feel stay in the background of our pollinator discussions and are massively underappreciated, despite their important role in our ecosystems. Come with me to give hoverflies the recognition they deserve.

What are hoverflies?

With over 100 species in Maryland, hoverflies (sometimes also called flower flies, or simply syrphids) are a group of flies that belong to a family of insects called Syrphidae. They are called hoverflies because they are very good fliers, able to quickly change directions or maintain their flying positions in very impressive ways. While their larval stages can have a huge variety of nutritional needs (some of which make them great biological control agents of pests), a very large number of the species are strongly associated with flowers as adults. In fact, the females require nectar and pollen consumption for their ovary development, making them depend strongly on floral resources for reproduction. For this reason, they act as important pollinators of many wild plants and crops, especially in temperate climates. Although not fully recognized by the general public, pollinating hoverflies have been shown to contribute globally to the pollination of over 70% of crops globally and about the same percentage of European wildflowers (few studies have evaluated the latter in North America)! You can learn more about this in this recent publication.

Hoverflies can be recognized by their large eyes, short antennae, and at rest their wings positioned perpendicularly to their body, as seen here in this (likely calligrapher or Toxomerus) hoverfly from Maryland. Photo: A. Espíndola

Ecology and biology of hoverflies

I hope that you’re now starting to get excited about these little creatures. Before you run outside to try to catch a glimpse of them, let me tell you some more about their lives, so you can continue to be amazed at what they do and why I am on a “pollinator recognition” mission for them.

As I was saying before, a vast majority of hoverflies are strongly associated with flowers. This makes them potentially important pollinators, and this is indeed true for many of them. However, there’s another reason why they are so important: their ecology. In fact, hoverflies have migratory or at least long dispersal behavior. This means that they have great potential for long-distance dispersal of pollen, and thus can contribute strongly to the pollination of plants that may be spatially far away from each other. Thinking about pollination and its role in plant reproduction, such long-distance pollen dispersal can be key in the reproduction of isolated plant populations, and even in increasing and maintaining genetic diversity in those populations. All of that tends to positively impact the ability of those plants to maintain their populations, making hoverflies key actors in sustaining the diversity of many wild plant species.

And also, because I really want to make an impression on you 😊, know that when I talk about hoverfly migration, I am talking about migration patterns that can in some cases be equivalent to those of more “famous” insects, such as monarchs. Some studies have shown some hoverfly species migrate thousands of miles, following the seasons. Although this is relatively well-studied in Europe, we know that similar migration patterns also occur in other parts of the globe, including North America. And as a fun fact, in our research group at UMD, we believe that we once observed and sampled a wave of migration of hoverflies right here, while studying pollination interactions in the endangered serpentine grasslands of Maryland.

a fly that looks like a bee with large black eyes

a syrphid fly that looks similar to a bumblebee

a syrphid fly has yellow and black stripes and two wings
Hoverflies often trick us into thinking that they are something they are not. Here we have some great examples of elaborate mimics of bees/bumblebees and wasps. Can you spot the traits that give them away? Top: Bare-eyed bee mimic (Mallota bautias); center: Hairy-eyed bee mimic (Mallota posticata); Bottom: Transverse-banded flower fly (Eristalis transversa). Photos T. Shahan, M. Wills, J. Gallagher. All CC.

How to recognize them?

Perhaps a reason why hoverflies are underrecognized is that many of their species display impressive body mimics of other species, many of which people tend to be afraid of because of their stingers. For example, some of the most common hoverflies in our area display yellow and black stripes, tricking us (and potential predators) into believing they are in fact wasps or bees. This is a strategy that protects them from predation but also requires us to be more attentive when we are trying to find them.

Despite this, there are some simple ways to recognize their trick. Because they are flies, hoverflies have characteristics that differentiate them clearly from other groups of insects, such as wasps. One of the main traits to look for when trying to figure out if we are facing a hoverfly (vs. a wasp, for example), is looking at their wings. Unlike bees and wasps, flies have only one pair of wings, which at rest they usually extend perpendicularly to their body, which makes them look like a plane or a “T”. Wasps and bees, on the other hand, typically don’t do this, and they fold their two pairs of wings flat over their abdomen while they are at rest.

Another way to tell them apart from most other wasps and bees is their heads (this may be also useful when the wing trait is not easy to see). In fact, flies generally have VERY large eyes (just think about any fly costume 😉). Hoverflies are no exception! They also have large eyes that cover a very large part of their heads, as well as very short antennae. On the other hand, bees and wasps, usually have much much longer antennae that extend way beyond their heads.

Ready to go out and find some of them? Remember that you can always check out iNaturalist to help you out with identifications! Good luck!

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!

An Ode to Beebalms, Our Beautiful Biodiversity Magnets

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Scarlet beebalm (Monarda didyma). Photo: A. Espíndola

Among the many native plants of North America, there’s one that every summer stuns me with its beauty and its important role in our ecosystems and our lives. In today’s post, I want to share some information about a lovely group of plants local to right here, which can be easily grown in our green spaces, and which one can observe flowering right now: beebalms!

What are beebalms?

Beebalms are a group of plants in the mint family (Lamiaceae) that belong to the genus Monarda. This genus is restricted to North America and includes several species. In Maryland, there are at least four species present, one of which (M. clinopodia, the basil beebalm) is currently listed as requiring conservation actions (listed as Vulnerable). The other three species (M. didyma, M. fistulosa, M. punctata) appear to be relatively common in the region and are easy to grow in our green spaces. All species reach about 2 to 5 feet in height and are great additions to flower beds because of their beauty but also because they act as biodiversity magnets. For example, the genus Monarda has been recognized as supporting at least three rare and specialist bee species in the Eastern USA, and attracting a lot of natural enemies of pests, meaning that providing these floral resources can support the populations of bee species that depend on the pollen of these plants for their nutrition and help us naturally control pests in our green spaces. And last but not least, later in the season their fruits support birds and, if left uncut, their stems offer overwintering spaces for arthropods.

Scarlet beebalm (M. didyma)

This is a perennial species with dark red flowers that bloom during the summer. As for all beebalms, the flower heads are formed by many elongated flowers that harbor abundant nectar. The plant is incredibly attractive to pollinators, acting as a magnet to bees of all sizes, butterflies, and hummingbirds. Besides its great support to pollinators and other arthropods, this species (along with M. fistulosa) has medicinal properties, which have been identified and used since immemorable times by Native Americans. The very name of beebalm is even related to these uses, since the plant can be used to produce poultices that help with skin affections, including bee stings. Preparations of the plant are also traditionally used to help with digestive and respiratory issues. Finally, as for many mint plants, this species is rich in essential oils, which makes it a good one to flavor foods like one would do with oregano and mint. You can learn more about how to grow this species, along with other facts on this USDA information sheet.

a stand of brightly colored red flowers - monarda didyma

Scarlet beebalms display red flower heads that offer abundant nectar to a large variety of vertebrate and invertebrate pollinators. Photos: A. Espíndola, J. Schneid (CC)

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