By: Kristen Morrow, JCC Naturalist
While out walking my dog around my Iowa City neighborhood last weekend, I stopped to enjoy one of my favorite springtime events: the emergence of ground-nesting bees. Every year in early April, I notice these frenetic bees out and about for the first time. For those unacquainted, this event appears as clouds of insect activity, buzzing around near the ground amidst patches of bare soil. When I saw them this year, I squatted down to observe, right there on the sidewalk, for over ten minutes, watching with fascination as the bees crawled in and out of their tunnels (surely, drawing equal fascination from the residents of the houses nearby, who may have been conducting their own observations from behind their blinds of the peculiar naturalist outside).
I am not 100% certain, but after doing some research, and using clues of behavior, seasonality, and general appearance, I think that this springtime passage I enjoy so much may be the activity of cellophane bees, possibly that of a gregarious species called the Unequal Cellophane Bee (Colletes inaequalis).
Most readers likely have never heard of such a creature as a cellophane bee – I certainly hadn’t until a few years ago. For a long time, when anyone said the word “bee,” most of us conjured up images of a honey-making, colony-dwelling honeybee, an insect not native to North America (yet, which has high support to become the state insect of Iowa). Don’t get me wrong, I love honeybees, mainly because I love a good jar of local honey. Still, I’m happy to report that the honeybee is increasingly having to share the stage, as more of us are aware of the incredible diversity of our native bees each day.
Worldwide, there are over 20,000 species of bees (only a handful of which make honey). In the U.S. and Canada, there are 4,000 species, and here in Iowa, we have between 300 and 400 species of native bees.
The vast majority of bees do not live in a shared colony, but rather are considered “solitary.” Most solitary bees (70%) are ground-nesters, meaning that they live in little tunnels in the ground, like the bees I observed on my walk. The other 30% of solitary bees are cavity-nesters, nesting in little tunnels in tree trunks or in the center of plant stems. Some solitary bees are gregarious, meaning that, even though females use individual nests, hundreds to thousands of these nests may be found together in a concentrated area.
Among solitary bees, each female creates her own nest and works alone to find food for her future offspring. This food, called “bee bread,” is made from a mixture of pollen and nectar. As each bundle of bee bread is complete, she provisions a nest cell, lays an egg, and then gets to work on the next cell. Once she has finished laying eggs, her mothering role is complete, and she flies away.
While I was observing the bees along the sidewalk, I had no fear of being stung. Any species of bee can sting (only females sting), but solitary bees are very unlikely to do so. With no colony to protect, they have little reason to sting unless they feel directly threatened, usually by being handled or getting tangled up in clothing. So long as you are gentle, these bees can be fun and safe to observe, even up close!
Once you are aware of the huge array of bee diversity, you start to notice that they are everywhere! It becomes an exciting fascination to wonder about who they are and what their lives are like. Check out the following selection of Iowa native bees, and keep your eye out for them this spring and summer!
Cellophane Bees Colletes sp.
Cellophane bees are so named because of their cellophane-like nest lining. The female creates this waterproof material through a mixture of saliva and a special secretion, then paints the material onto the walls of the nest cells. The material prevents the egg and its provisions (which are uniquely liquid) from drying out, flooding, or spoiling. (Check out some photos of these nests here.)
Cellophane bees are some of the earliest to emerge in the spring. Males emerge first, and can be found in large numbers flying low to the ground, seeking later emerging females to mate with (I think this is probably what I was witnessing next to the sidewalk). The species that emerge in the spring will develop throughout the summer and fall, and overwinter in their nest cells as adults, before the cycle starts all over the following spring.
Leafcutter Bees Megachile sp.
Leafcutter bees are, without a doubt, my favorite bees. Their genus, Megachile, means big lipped, and refers to their large mandibles, which they put to work to cut leaves. These bees are primarily cavity-nesting. They construct individual cylindrical nest capsules out of leaves or petals. To create the capsules, the female cuts out ovals from her plant material of choice. The ovals are rolled up into a cylinder; once the female has placed the provision of bee bread and laid the egg, she caps the cylinder with a cut-out leaf/petal circle. Multiple capsules are stacked end-to-end in the nesting cavity.
In late summer, I often spot the circle and oval cuttings made by leafcutter bees. Though many different kinds of plant material may be used, they most commonly use the leaves of tick trefoils, roses, St. John’s wort, ash, and redbud. One study of leafcutter bee nests found that the majority of plant materials selected for the capsules had antimicrobial properties.
Most species of leafcutter bees share some distinguishing traits. The females have broad flattened abdomens with thick hairs underneath, used to collect pollen. Males do not have the under-abdomen hair, but do have long hairs on their forelegs.
Watch a pretty cute video of a leafcutter bee emerging from her leaf capsule.
Golden Sweat Bee Augochlorella aurata
Many people are shocked when they hear that bees can be green. In fact, bees are represented by a whole rainbow of colors! Sometimes, those colors can even vary among the same species, as it does with the Golden Sweat Bee. Though these bees are a shimmering golden green here in Iowa, the same species can be a stunning deep purple along the coasts of the deep South.
This species is one of the most common bees in the eastern U.S. They are most readily found through July and August, especially in open grasslands and fields.
Green Metallic Sweat Bee Augochloropsis metallica
Augochloropsis metallica is another beauty. Green Metallic Sweat Bee is a common name that is used for multiple species, all with the same shimmering emerald hue. The wide variety of shiny green bees can be challenging to distinguish. Technical details on the eyes and face are useful for determining identity among the similar genera. All of the Green Metallic Sweat Bee species are quite small, ranging from about five to 12 millimeters long.
Squash Bee Peponapis pruinosa
If you grow pumpkins or squash, be sure to peek into their flowers this summer – you may find a Squash Bee working inside! Squash bees specialize on plants in the Cucurbita genus, and they are the most efficient at pollinating these vegetables. These hardworking bees are also early risers, starting their foraging day before dawn (when few other bees are out) to reach the newly opened squash blossoms, and working until the blossoms close around mid-morning.
My favorite thing about Squash Bees: Both males and females can be found napping inside squash flowers! Males regularly sleep inside the blossoms, and females will nap inside them before she establishes a nest of her own.
Rusty-patched Bumble Bee Bombus affinis
This bee is especially noteworthy. In 2017, the Rusty-patched Bumble Bee was listed as an endangered species under the federal Endangered Species Act. The listing was historic as the first bee to join the list. This species has declined by an estimated 87%, with most of the sudden decline taking place in just the last 20 years. Their range, which once included 31 states spread between the Midwest and along the East Coast to the Northeast, has now shrunk to small populations in just 12 states.
While the Rusty-patched Bumble Bee is the first bee to be listed as endangered, it is not alone in its vulnerability. One in four of the 46 bumble bee species in North America is at risk of extinction, including three other species in Iowa.
The male and worker Rusty-patched Bumble Bees can be distinguished by a band of rusty orange on the middle of the second abdominal segment. Those new to bumble bee ID, might confuse it with somewhat similar looking bees, such as the Tri-colored Bumble Bee or the Red-belted Bumble Bee. Check out this Iowa specific guide to learn identification tips.
After seeing all of these gorgeous and fascinating bees, you may be wondering what you can do to help them thrive. Take the following steps to become a bee steward:
1.) Plant native flowers. The importance of establishing and expanding native habitat cannot be underscored enough. Planting native plants will provide a significant health boost for the web of life generally, not just for the bees. While non-native flowers can be helpful as well, the nectar and pollen resources in native plants are more nutritious for pollinators. Native plants also serve as host plants for other pollinators like butterflies and moths. You might be wondering where you can find native plants. Good news – there are many regional nurseries, including popular nurseries in Iowa, Minnesota, and Wisconsin, that specialize solely in the production and sale of native plants. Check for availability with your favorite local garden center as well.
2.) Leave the leaves. Leaf litter is valuable overwintering habitat for some types of bees, including queen bumble bees. If you feel the need to rake leaves, rather than removing leaves entirely, consider redistributing them to other parts of a yard, such as undisturbed corners, as a covering for flowerbeds and gardens, and as mulch around trees.
3.) Provide nesting sites. The majority of bees nest in tunnels in the ground or in cavities in wood and plant stems. To aid the ground-nesting bees, leave some areas of bare ground. To aid cavity-nesting bees, leave flower stems standing throughout the winter and into the spring. Wait until consistent warm temperatures to remove the stems in preparation for the next growing season. You can also use logs intentionally within the yard and garden, as a substrate for cavity-nesters. Use caution when providing artificial “Bee Hotels.” If not properly cared for, some can cause more harm than good.
4.) Avoid pesticides. Consider refraining from using lawn and garden chemicals of all kinds. Avoid establishing new pollinator habitat if there is high pesticide use nearby. When purchasing established plants, look at tags and avoid plants that were treated with neonicotinoides, a group of insecticides that are absorbed into plant tissues and can be present in nectar and pollen resources.
5.) Be a citizen scientist! Help track bumble bee populations by submitting photos of bumble bees you observe to Bumble Bee Watch.
The bees included in this post, barely scrape the surface of Iowa’s incredible bee diversity. To learn more about our fascinating native bees, I highly recommend Bees: An Identification and Native Plant Forage Guide and The Bees in Your Backyard as two wonderful resources.
Happy bee watching!