Archives For Nature in View

The surprising science behind hummingbirds and flowers

Do they have a “type,” or it is just economics?

Guest Blogger —  October 30, 2018 — 4 Comments

Fast and graceful, hummingbirds flit from flower to flower—but which ones and why? A Chicago Botanic Garden scientist and his collaborators recently made some unexpected findings on the subject.

It’s a common perception that plants are perfectly matched to their pollinators and that each pollinator has a specific flower type that they are attracted to. For hummingbirds, many gardeners and scientists alike have long assumed their flower type to be one that is strikingly red, tubular, and scentless.

Flowers that are often thought of as typical choices for hummingbirds:

Wyoming paintbrush (castilleja linariifolia)

Wyoming paintbrush
Castilleja linariifolia

Giant red paintbrush (castilleja miniata)

Giant red paintbrush
Castilleja miniata

Scarlet gilia (lpomopsis aggregata)

Scarlet gilia
Ipomopsis aggregata

It’s not hard to see why anyone might assume that hummingbirds and certain kinds of flowers are perfect matches. Hummingbird visits to flowers are visually striking, and many casual observations suggest a typical and consistent set of floral characteristics associated with this plant-pollinator interaction. The vibrant red or orange color of blooms appear as if they were designed specifically to attract the eye of hummingbirds. A hummingbird’s long bill appears perfectly matched for the extraction of nectar from the long, tubular flowers. But don’t be fooled—while it’s satisfying to organize flowers and pollinators and their interactions into clear-cut categories (known as pollination syndromes), these human constructs may mask what is really going on in nature.

Many “typical” hummingbird flowers belong to species that produce diluted nectar with lower sugar concentrations. Yet the hummingbird’s signature hovering flight burns massive amounts of calories. From the hummingbird’s perspective, it would therefore be much more efficient to drink from flowers with more concentrated nectars. Hummingbirds are also known to have acute color vision and show no innate preference for the color red—in other words, there is no reason for them to exclusively focus on red or orange flowers. And their long and slender bills are perfectly capable of extracting nectar from both long and shallow flowers. Finally, hummingbirds do have a sense of smell. So why would hummingbirds go out of their way to visit a limited selection of reddish, long-tubed, scentless flowers that produce cheaper nectar when they could feed from more suitable nearby sources in a diverse buffet of flowers?

Flowers that are “atypical,” or lacking the characteristics we associate with hummingbird-visited flowers (note that they vary in color, shape, odor, and nectar concentration):

Nuttall’s larkspur (delphinium nuttallianum)

Nuttall’s larkspur
Delphinium nuttallianum

Glacier lily (Erythronium grandiflorum)

Glacier lily
Erythronium grandiflorum

Ballhead waterleaf (Hydrophyllum capitatum)

Ballhead waterleaf
Hydrophyllum capitatum

The Garden’s  Paul CaraDonna, Ph.D., and his research collaborators Nickolas Waser, Ph.D., and Mary Price, Ph.D., of the Rocky Mountain Biological Laboratory, discovered that it all comes down to the basic economics that maximize energetic gain at minimal energetic cost. While camping and conducting research across the American Southwest, the three researchers kept observing something curious and unexpected: hummingbirds routinely visited flowers that lacked the expected typical characteristics of hummingbird flowers.

To make sense of these observations, the team dug back into their field notes from the past four decades and began to look more closely at the potential profitability of atypical vs. typical flowers for hummingbirds. Their field notes contained information on hummingbirds’ foraging rates at flowers and measurements of the nectar sugar concentrations; with this information, the team was able to calculate the energetic profits that could be gained by a hummingbird foraging at either type of flower.

How do hummingbirds choose flowers?

A broad-tailed hummingbird (Selasphorus platycercus) feeding from the so-called “atypical” flowers of pinedrops (Pterospora andromedea). Photo courtesy: Audrey Boag

What the team found was that typical and atypical flowers overlapped considerably in their energy content and profitability for hummingbirds. In other words, most typical flowers were no better than most atypical flowers and most atypical ones were no worse than most typical ones. Taken together, this research reveals that hummingbirds are making an energetic profit—not a mistake—when visiting these atypical flowers. In fact, atypical flowers may play a critical yet underappreciated role in supporting hummingbird migration, nesting, and populations in areas that seem to be lacking in suitable floral resources. The results of this research were recently published in the peer-reviewed scientific journal The American Naturalist. Neither typical nor atypical flowers are categorically better or worse than the other, and instead show considerable overlap in the energetic gain they offer to foraging hummingbirds.

Many hummingbird conservation efforts focus solely on typical flowers. Perhaps you have come across suggested hummingbird plant lists that are dominated by typical species. Now knowing that atypical plants can support the migration and residence of hummingbirds, we can consider more than just the typical plants as food resources in habitats and along migration routes.


Karen Wang

Guest blogger Karen Wang graduated with a B.S in ecology and evolutionary biology and a B.A in creative writing from the University of Arizona in 2017. She has worked as a research assistant on a variety of projects, mostly involving pollinators such as bees and moths. 


©2018 Chicago Botanic Garden and my.chicagobotanic.org

Dragonflies capture summer

Carol Freeman —  September 13, 2018 — 1 Comment

Summer won’t be over for a while in my book—not as long as there are dragonflies around. I think I’ve seen more dragonflies this year at the Chicago Botanic Garden than I have in the past ten years combined. The quick, strong fliers seem to be everywhere. 

Female Eastern Pondhawk

Eastern pondhawk dragonfly, female. Most dragonflies have very different-looking males and females. This one was in the Native Plant Garden. Photo ©Carol Freeman.

Some of the dragonflies migrate south toward the Gulf Coast through September and maybe beyond. With the help of citizen observers, scientists are studying the migration patterns of this fascinating insect, which has a near 360-degree field of vision that helps it avoid predators.

The most abundant dragonfly I’ve seen this year is the Eastern pondhawk, with blue dasher dragonflies coming in a close second. I’m also seeing quite a few damselflies, which are generally smaller and more thin-bodied than dragonflies and tend to hold their wings above their bodies. (See my blogpost Damselflies 101 for more information.)

Female Blue Dasher Dragonfly

Blue dasher dragonfly, female. She looks very different from her male counterpart. Photo ©Carol Freeman.

Male Blue Dasher

Blue dasher dragonfly, male. Hanging out on the waterlilies. Photo ©Carol Freeman.

Dragonflies and damselflies, both in the order Odonata, can spend several years as aquatic nymphs before they emerge into the beautiful winged insects we see on land, which is why you will often see them around water. They are fierce hunters in both stages. They don’t bite or sting humans, though.

Green Darner

The common green darner dragonfly is one of the first dragonflies to emerge in the spring, and one of the species that can be found migrating in huge swarms in the fall. Photo ©Carol Freeman.

Dragonflies can be found here from March through the first hard freeze in the fall. Right now, you might even be lucky to find yourself in the middle of a migrating swarm of green darners, black saddlebags, or wandering gliders as they head south. About 90 different odonates can be found in the Chicago area. Each one is a delight to behold.

Eastern Amberwing

Eastern amberwing dragonfly, male. This is one of the smallest dragonflies in our area, at just more than 1 inch long. Photo ©Carol Freeman.

Widow Skimmer

Widow skimmer dragonfly, male. This is one of the larger, flashier dragonflies, and it is easy to identify. Photo ©Carol Freeman.

Eastern Forktail Damselfly

Eastern forktail damselfly, female. This is the most common damselfly in our area, and it can be found in the Dixon Prairie. Photo ©Carol Freeman.

Dragonflies are territorial and will often chase off other dragonflies, only to return to their favorite perch. A favorite place to find them at the Garden is around the waterlilies and lotus blossoms, but you can spot them throughout the 385-acre grounds. Drop by and keep an eye out for the dragonflies near the late-summer blooms. 

Skimming Bluet Damselfly

Skimming bluet damselfly, female. This is a small, delicate damselfly found in the Dixon Prairie.
Photo ©Carol Freeman.

Slender Bluet Damselflies

Slender bluet damselflies, getting ready to lay some eggs. I found this pair along the shoreline next to parking lot 5.
Photo ©Carol Freeman.

©2018 Chicago Botanic Garden and my.chicagobotanic.org

At Butterflies & Blooms on Monday, I saw something I had never seen before in my five years as a butterfly wrangler at the Chicago Botanic Garden. I noticed that a leopard lacewing’s right wings were bright orange, just like any other male of the species, but the left wings were beige—only females have beige wings. This lacewing was half male and half female, or a gynandromorphic butterfly.

Underside of the gynandromorphic leopard lacewing

Underside of the gynandromorphic leopard lacewing

Topside of the gynandromorphic leopard lacewing

Topside of the gynandromorphic leopard lacewing

That morning, when I had discovered the male-female lacewing, butterfly visitors had been waiting for me to release butterflies from the pupae chamber. So I packed up the lacewing, with all of the other newborns. I then released each of the two dozen butterflies that had hatched that morning, saving our special discovery for last. I got everyone’s attention and announced, “This is extremely rare! As a butterfly wrangler, I have released many thousands of butterflies, but this is the one and only butterfly that is literally half male and half female!” The visitors were fascinated by the lacewing, which sat on the tip of my finger. Then it took flight and was free in the blink of an eye. Luckily, one of our volunteers snapped some beautiful photos.

Later, it occurred to me that this specimen could actually be a valuable contribution to science, and if nothing else, something that everyone should get a chance to see. I tried to find and capture it so an expert could take a closer look. A full day went by without anyone seeing it. I was afraid we had missed an opportunity to contribute something special to the scientific community, but our luck was about to change. 

On Wednesday morning, I was chatting with a young butterfly enthusiast about the gynandromorphic lacewing. I asked him if he could keep an eye out and possibly help me find it. He said, “Oh, you mean like this one?” He turned and pointed to the rare creature, which was sunbathing just behind his head. I couldn’t believe it. I offered to name the butterfly after him, but he modestly declined. I’m still trying to reach out to experts. Meanwhile, after that, I brought the special butterfly back into the pupae chamber, where it has been on display to visitors. I have been feeding it by hand, using a piece of foam dipped in fruit juice and Gatorade, which the butterfly seems to love.

Here is a little information about gynandromorphism. Gynandromorphs are very rare, but can be found in birds, fish, crustaceans, and butterflies, among other organisms. Usually, gynandromorphs have an uneven mixture of male and female features, but our special butterfly has an even rarer form of gynandromorphism because the male and female traits are bilateral, meaning they are split perfectly down the center of the body. How rare are we talking? In a 1980s study, only five out of 30,000 butterflies displayed gynandromorphism.

So how does gynandromorphism occur? There are several possibilities having to do with mishaps that occur during early cell division. Butterflies have a W and a Z chromosome for female and male, respectively. Sometimes, the W and Z chromosomes get stuck together during cell division, resulting in a mixture of male and female traits. In another scenario, the embryo is “double fertilized,” resulting in both female and male nuclei throughout the organism. The causes include bacterial or viral infections, ultraviolet radiation, and other environmental factors that can alter an organism’s DNA during division and growth.

In any case, it’s cool to have a butterfly with such a rare deformation that is still fully able to exist as a healthy adult, sipping nectar and basking in the adoration and fascination of its fans. We have not yet named this butterfly, so please leave some suggestions. The typical lifespan of an adult butterfly is about two weeks, so drop by Butterflies & Blooms and say hello to our newest celebrity.


©2018 Chicago Botanic Garden and my.chicagobotanic.org

Bees in the Big City

Andrea Gruver —  August 15, 2018 — 3 Comments

The plants you see from your train seat on the Metra Union Pacific North line may help conservation scientists learn about how urban areas impact native bees.

Although most people think of honeybees when they think about bees, there are more than 4,000 native bee species in the United States and 500 species in Illinois alone. Like their honeybee counterparts, native bees are undergoing global declines, making them an important conservation concern. With the growth of urban areas, native bees may be faced with new challenges, yet we don’t know the extent that urban areas impact native bees.

My research at the Chicago Botanic Garden is investigating how urban areas may affect native bees in Chicago. Chicago is an ideal city to study the impact of urbanization on native bees because the intensity of urbanization slowly wanes from the urban core of the city out into the surrounding suburbs.

Megachilid (leaf cutter) bee

My research is focused on native bee species in Illinois like these Megachilid(leaf cutter) bees.

Megachilid (leaf cutter) bee

Part of that research is about bringing public awareness to the other native bees we have around Chicago.

To explore native bee communities along this urbanization gradient, I have a series of eight sites along Chicago’s Union Pacific North Metra (UP-N) railway. I chose the sites along the rail line because they followed a perfect gradient from very urban to very suburban. I was also drawn to them because most of the vegetation around the sites is unmanaged and composed of similar species.

All of the sites vary in the levels of green space and impervious surface (concrete/buildings) surrounding the sites. Sites near downtown are surrounded by nearly 70 percent impervious surface, while sites near the Chicago Botanic Garden are surrounded by just 15 percent impervious surface.

[Click here to view video on YouTube.]

Studying bees in this area along the Metra line allows us to ask a variety of questions about native bees. For instance: Are there fewer bees in highly urban areas? Are there different bees in natural areas compared to urban areas? Do the bees in highly urban areas have different traits than those in natural areas?

Pollinator Collection Near the Metra with Andrea

Andrea and an intern collect bees along the Metra line.

This summer, a few interns at the Garden and I have been gathering and sampling bees at each of my eight field sites. To catch the bees, we use two methods. First, we set out fluorescent colored bowls with soapy water that attract and capture the bees. Secondly, we use a butterfly net to capture bees at the site throughout the day. When we are finished sampling, the bees are taken back to the lab at the Garden’s Daniel F. and Ada L. Rice Plant Conservation Science Center and pinned for future study.

In addition to collecting the bees, we also record all of the flowering plants and count how many flowers are blooming at the sites.

Although our days are currently filled with fieldwork and pinning, in the fall we will spend almost all of our time in the lab identifying the bees down to the genus or species level. When we have all of the bees identified, we can then start analyzing the data for my master’s thesis and answer some of the questions we have put forth. We suspect we will see a higher abundance and diversity of bees in sites located in more natural areas with more flowering plants.

My research will help us understand how urban areas are shaping native bee communities and help us determine what landscape features promote native bee diversity in urban environments, some of which can be implemented in urban restoration projects. We also hope that this work will illuminate the amazing diversity of native bees we have here in Chicago.


©2018 Chicago Botanic Garden and my.chicagobotanic.org

One day at Butterflies & Blooms, I noticed a crepuscular, cosmopolitan imago puddling in order to prepare for an upcoming lek. What did I just say?

The vocabulary surrounding Lepidoptera can be very specific—and not so easy to understand. Let’s break it down, and go over some of my favorite butterfly and moth terminology (and learn some of the amazing things these insects do). Then, see if you can decode the sentence above. 

Painted Lady (Vanesa cardui)

The very cosmopolitan painted lady (Vanesa cardui)

Cosmopolitan—In this case, a cosmopolitan is not a mixed drink or a well-traveled individual—although this term is related to being in many geographic locations. “Cosmopolitan” describes a butterfly species that is found worldwide. The painted lady is considered cosmopolitan; it is found on every continent except Australia and Antarctica.

Crepuscular—Crepuscular species tend to be most active at dawn and dusk. At Butterflies & Blooms, we have a few species that prefer to fly around during the early morning and late afternoon, when the sunlight is less intense. Species such as the giant owl, as well as other butterflies in the genus Caligo are considered crepuscular based on this behavior pattern.

Diapause—Here in the Midwest, many people wonder how butterflies survive the winter. The answer is diapause. Chrysalids can feel and respond to the temperature outside of their protective exoskeletons. If they notice a few cold nights, they will react by going into a dormant phase called diapause. When this happens, they cease development, and the shell of the chrysalis will turn brown and harden; this is how they survive the overwintering. Many pupae are green in order to blend in with the surrounding foliage, so it makes sense that they would turn brown in the winter to blend in with the dead, brown foliage. When the warmth and light of spring return, they become green again and complete their metamorphosis into adult butterflies.

PHOTO: Danaus chrysippus chrysalids

One of these Danaus chrysippus chrysalids is not like the others. Did it begin to enter diapause during shipment? Or did this African queen butterfly begin its pupation in an area without typical greenery? We are still learning ourselves.

Eclosion—Here at Butterflies & Blooms, we normally refer to our butterflies as “emerging” or even “hatching” from their pupal state. The correct scientific term for this is actually “eclosion.” If you want to impress (or possibly annoy) your friends, tell them that when chrysalids complete their diapause, they resume metamorphosis, and eclose into adult imagos

Frugiverous—Butterflies such as the ever popular blue morpho, giant owl, and the great orange deadleaf are frugiverous; they come from habitats where there aren’t many wildflowers available, so they turn to feeding solely on fruit instead. This is why we have trays of fermented fruit in the exhibit.

PHOTO: monarch butterfly on fruit tray.

A selection of watermelon, banana, grapefruit, and orange slices are an attractive source of food to frugiverous butterflies like this monarch.

Generalist vs. Specialist—Some butterflies are successful because they “specialize” in certain plant families. This means that their success is somewhat tied to the success or failure of the particular plant they evolved to rely on. This is the case for monarch butterflies. Monarchs have evolved to rely on plants in the milkweed (Asclepias) family as both a nectar source and host plant on which to lay eggs. Although there are many different types of milkweed, this is still considered a niche. On one hand, this can be a benefit, because the monarch can capitalize on the unique benefits that come from plants in the milkweed family. On the other hand, if milkweed declines, monarchs don’t have any alternative plant families to use as hosts.

Generalists, such as the painted lady, can use a wide variety of plants families to lay eggs on, such as carrots, mints, and nettles. This ensures that they will always be able to find suitable host plants. Humans are also generalists, as we are able to use a wide variety of food sources and habitats.

Imago—While we simply refer to our butterflies as “adults,” the true term for the final stage of butterfly development is “imago.” The life stages of a butterfly are egg, caterpillar (larvae), chrysalis (pupae), and adult (imago). Interestingly, the term “imago” also refers to a human individual’s idealized image of himself or herself. What’s your personal imago?

Lekking—This is a very interesting term, because until the blue morpho was discovered, lekking was not thought to be a behavior found in butterflies. Lekking is a type of mating ritual in which all the males form a group and compete, showing off their most admirable features. The males with the right stuff will be the ones who get to mate and pass on their genes. With blue morphos, only the most colorful males will get this privilege. I once witnessed a group of blue morphos “lekking” at Butterflies & Blooms. A group of about ten males were hypnotically circling around a single female. I couldn’t believe my eyes!

Polymorphism—Some of our butterfly species display polymorphism, including the mocker swallowtail and the postman. This means that within the species, the wings can have numerous pattern variations. This can make their identification tricky. The postman butterfly (Heliconius melpomene) is intensely studied by Lepidopterists because its patterning is more variable than any other butterfly species on earth. Here at Butterflies & Blooms, we have observed at least four distinct patterns from this one species of butterfly. Some have a white “skirt” along the bottom of their hind wings, some have a red spot on each forewing, and yet others have a pair of red spots on each wing.

Heliconius melpomene aglaope

Heliconius melpomene aglaope

Heliconius melpomene melpomene

Heliconius melpomene melpomene

Heliconius melpomene amaryllis

Heliconius melpomene amaryllis

Puddling—Puddling is the tendency of butterflies to sit in wet soil or stone and extract the minerals from the ground. Apparently, puddling is somewhat exclusive to male butterflies, because they need these minerals for sperm production. This is also why the butterflies (especially males) land on visitors. They drink our sweat to obtain these precious salts, sometimes absorbing them directly through a t-shirt!

Blue-spotted Charaxes (Charaxes cithaeron)

A blue-spotted charaxes (Charaxes cithaeron) puddles in gravel after a brief rain shower

Sexual Dimorphism—Butterflies tend to have different color and sizes based on whether they are male or female. This phenomenon is known as sexual dimorphism. Because female butterflies lay eggs, they tend to be a bit larger than the males. The males tend to have richer coloration and/or bolder patterns. Just like birds and fish, females will tend to choose the males with the boldest colors, as this indicates healthy genes.

Male leopard lacewing (Cethosia cyane)

Male leopard lacewing (Cethosia cyane)

Female leopard lacewing (Cethosia cyane)

Female leopard lacewing (Cethosia cyane)

These are just a handful of terms I like to use when talking about our amazing collection of butterflies. Expect to be quizzed on them during your next visit to Butterflies & Blooms!


Postman comparison images by Notafly (self-made Own photograph.Studio.Nikon.) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons

Flame-bordered charaxes (Charaxes protoclea) and blue-spotted charaxes (Charaxes cithaeron) ©Patty Dodson

©2018 Chicago Botanic Garden and my.chicagobotanic.org