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Cellophane bees are the real first sign of spring

Step aside robins, unequal cellophane bees (Colletes inaequalis) are the true harbingers of spring in the eastern US. Bees emerge on the first warm day, often when snow is still on the ground, and they refuel on flowers after a long winter. And, they are already out in Boston: in 2022, cellophane bees emerged on March 16th!

Unequal cellophane bees are incredibly abundant, especially in suburban areas, so they are easily spotted around town. Before you head out to find them, read this blog, check out this video, and explore our field identification guide. After you enjoy your time with them, be sure to report photos to iNaturalist!

Colletes inaequalis female sits in her nest entrance, ready for spring. Females dig long tunnels underground 1-2 feet in length!

Flight Season

Unequal cellophane bees are active in very early spring, usually before trees have leafed out, and are active for four to five weeks. In Massachusetts, they are typically active from mid-March through mid-April.

Appearance

Unequal cellophane bees are small—like macaroni, about 0.75x the size of a honey bee—with “cute” heart-shaped faces, sand-colored hair, and bold bands on their abdomen. Males have long antennae and thick mustaches. Females are bigger than males, with cleaner faces, shorter antennae, and long hairs on their legs for carrying pollen.

Colletes inaequalis are have bold stripes on their abdomens and have sand-colored hairs. Males (right) are smaller than females (left), with longer antennae and fuzzy mustaches.

Nesting habits

Unequal cellophane bees are easily spotted while nesting. Females build underground nests, excavating sand into a small mound at the surface called a tumulus (like an ant hill but with an entrance about the width of a pencil). They live in bee neighborhoods—termed aggregations—each of which can contain thousands of nests. In the first few weeks of the year, males can often be seen zooming low through the aggregation looking for mates.

Nesting aggregations typically appear on trampled, sandy south-facing slopes. Lakeshores, cemeteries, trampled picnic areas, sandy paths on the edge of the woods, and even backyards are all good places to look!

Cellophane bee nests occur in large aggregations, often in bare sandy soil. Each nest looks like a mini-volcano of sand, and females often sun themselves in the nest entrance.

Similar Species

Cellophane bees Colletes can appear similar to many mining bees Andrena that also nest below ground. But, Andrena have obvious facial foveae and parallel eye margins, which Colletes do not.

Comparison of Colletes vs. Andrena in the field.

Favorite Flowers

Unequal cellophane bees are not picky eaters. To attract them to your yard, plant spring-blooming trees like red maples Acer rubrum, apples Malus, eastern redbud Cercis canadensis, and serviceberry Amelanchier. They can also be spotted on garden bulb flowers like snowdrops, blue squill and crocuses.

Colletes inaequalis has a penchant for red maple (Acer rubrum) flowers.

Safety

You do not need to worry about being stung–cellophane bees are incredibly gentle! Even the biggest aggregations consisting of thousands of nests pose absolutely no threat to people or pets.

How to pick cultivars for pollinators

by Emily Erickson

Spring has finally arrived in the Northeast, and it’s time to start planting your pollinator garden! Perhaps you have already picked out the perfect spot in your yard and started making a list of which plants to purchase. Once you reach the garden center, you may be in awe of the different varieties to choose from. At the same time, you are faced with a familiar dilemma: are all these varieties equally good for pollinators?

What is a cultivar and why should I care?

Unless you are going out of your way to buy your plants from a specialty nursery, chances are you are purchasing a “cultivar,” or a plant that has been bred for desirable traits like the number of petals, flower shape, or flower scent. Plant breeding is not inherently a bad thing: it broadens the diversity of species that you can grow in your garden by improving resilience against pests, drought, or poor soils. As a result, cultivars have become the industry standard. They can be identified by the single quotation marks in the name (ex. Marigold Alumia ‘Flame’).

While cultivars are great for people, they are not always great for pollinators. Native plants and their pollinators share a long evolutionary history, and many flowers have evolved particular traits that signal honest advertisements of a high quality food resources. For instance, the smell and color of wild geranium tell a bee that that nectar and pollen awaits and the dark lines on the petals help them to quickly locate their meal.

In contrast, cultivars have been removed from evolutionary history with insects; humans have bred cultivars in labs and greenhouses to meet our aesthetic preferences. And sometimes, by selecting for traits that we deem impressive, we inadvertently produce plants that broadcast false advertising. Recent work, including my PhD research,  has demonstrated how cultivars—even ones that look quite visually similar—can vary dramatically in the abundance and diversity of insects that they are able to support1–6, so it’s important to choose carefully.

5 tips for choosing better cultivars

But, how do you choose? Ideally, all ornamental cultivars would scored for pollinator attractiveness to help guide customers to select high-value plants for their flower gardens. A metric like this doesn’t yet exist, however, so we’ve distilled down some basic guidelines that you can use to identify the best plants for flower-visiting insects!

1. Avoid doubled flowers

Double-flowered varieties are those that have been selected for extra petals, such as in many roses, impatiens, chrysanthemums, and carnations. Often, this doubling comes at a cost: the reproductive florets (where pollen and nectar are produced) are converted to petals, meaning the flower no longer feeds pollinators! And, even if the plant is still capable of producing rewards, doubling often obstructs visitor access to those resources6. So, while doubled varieties are interesting to look at, they are best left on the shelves.

2. Choose perennials and ‘nativars’

Recently, the commercial plant industry has shifted towards producing more cultivars of perennial plants, including many native species, or ‘Nativars’.7 These varieties are often rewarding to grow since they come back every year once established and they require less maintenance overall. My research found that many native and non-native perennial cultivars can be highly attractive to flower-visiting insects in the field. I even observed several rare and specialized species foraging on nativars! Some of the best pollinator-friendly nativars are also easy to find:

  • Oenothera ‘Fireworks’
  • Echinacea ‘Magnus’
  • Rudbeckia ‘Herbstonne’
  • Solidago ‘Fireworks’
  • Agastache ‘Blue Fortune’
  • Eupatorium ‘Gateway’

For tips on which native plants to source for your garden, check out TPI planting guides!

3. Choose cultivars that resemble wild types

A general guideline for selecting the best ornamentals is to go for cultivars that look most like the wild types. Of course, this is a subjective criterion, and there are many traits that we cannot readily perceive (such as scent or nutrition) that can influence plant attractiveness to pollinators. Still, in my research I found that pollinator attraction to the herbaceous perennial Catmint (Nepeta)—of which purple is the primary color found in the wild (Catmint is native to the Caucasus region)—was highest for purple compared to white cultivars. In other words, the less derived, the better!

4. Check the label

A major concern with ornamental flowers is the use of pesticides, particularly systemic neonicotinoids, during production. These pesticides can end up in the pollen and nectar treated plants and can have lethal and sublethal effects on visiting pollinators. Before you purchase a plant from the nursery, check the label to see if it has been treated with neonicotinoids!8

5. See for yourself!

One of the best ways to find ornamental cultivars that are attractive to pollinators is to walk through the garden center and notice which plants seem to be either getting the most pollinator visits or are visited by many different species! This will open your eyes to all the different pollinators that call our yards home and the wide array of plants that they like to use.

References

1.  Garbuzov, M. & Ratnieks, F. L. W. W. Quantifying variation among garden plants in attractiveness to bees and other flower-visiting insects. Funct. Ecol. 28, 364–374 (2014).
2. Erickson, E., Patch, H. M. & Grozinger, C. M. Herbaceous perennial ornamental plants can support complex pollinator communities. Sci. Rep. 11, 17352 (2021).
3. Erickson, E. et al. More than meets the eye? The role of annual ornamental flowers in supporting pollinators. Environ. Entomol. 49, 178–188 (2020).
4. Rollings, R. & Goulson, D. Quantifying the attractiveness of garden flowers for pollinators. J. Insect Conserv. 23, 803–817 (2019).
5. Marquardt, M. et al. Evaluation of the importance of ornamental plants for pollinators in urban and suburban areas in Stuttgart, Germany. Urban Ecosyst. 24, 811–825 (2021).
6.  Corbet, S. A. et al. Native or exotic? Double or single? Evaluating plants for pollinator-friendly gardens. Ann. Bot. 87, 219–232 (2001).
7.   Criley, R. A. Native fashion. Acta Hortic. 1167, 1–10 (2017).
8.   Erickson, E. et al. Complex floral traits shape pollinator attraction to ornamental plants. In Review.

The 5 best ways to make your yard pollinator friendly

by Atticus Murphy

Planting a pollinator garden is all the rage these days, but if you’ve never gardened before, it may seem like a daunting task. Don’t worry, it doesn’t have to be complicated! You can support pollinators in your yard by taking several easy and important actions. Tufts Pollinator Initiative has distilled it down to the 5 most important actions you can take today!

1. Plant a diverse set of flowering plants

Diversifying the flowers in your garden is the best way to support the most types of pollinators. Shoot for diversity on all levels: color, flower shape, size, and, most importantly, bloom time. Each pollinator species might only be active for a few weeks and visit a small number of plants, so adding flower diversity throughout the year will almost always boost your yard’s pollinator diversity (and give you blooms year round!). A good place to start? TPI’s top 10 flowers for bees! 

Diversity begets diversity: we’ve planted over 15 flowering species at our campus gardens and seen over 115 species of insect pollinators!

2. Add woody plants like trees and shrubs

Native trees and shrubs make excellent additions to pollinator gardens because they provide resources that herbaceous, perennial flowers often don’t. For instance: many native trees and shrubs bloom early in spring, at a time when few other plants are blooming on the landscape. In addition, trees and shrubs provide homes for solitary bees and many butterflies depend on tree leaves to complete their life cycles. As a bonus, trees and shrubs require very little maintenance after their first few years and provide shade for decades! To help you pick, check out TPI’s top 10 trees and shrubs for bees.

Unequal cellophane bees (Colletes inaequalis) depend on pollen and nectar from early-blooming red maple trees to complete their life cycles.

3. Grow native plants

To support our native pollinators, grow native plants. Our native pollinators have been in relationships with native plants for thousands of years, and sometimes have evolved such a picky diet that only one or a few native plant hosts will do. Avoid non-native ornamental plants (esp. doubled cultivars) like petunias and impatiens–they either offer unsuitable food resources, or have been bred to offer no pollen and nectar whatsoever. Compared to traditional ornamental plants, native plants can survive is less than ideal soils and periods of droughts, while still filling your garden with bursts of color. Pick up your locally-grown native plants at TPI’s summer plant sale!

fall bees fueling up on new england aster before winter
Native bees love native flowers like New England aster.

4. Minimize herbicide and insecticide use

It’s simple: to keep insect pollinators around, don’t apply pesticides. Herbicides kill the flowers that pollinators use for food. Leaving weedy flowers (“weeds”) to bloom creates abundant and diverse resources for pollinators. And insecticides like neonicotinoids are deadly for pollinators: remember, anything that kills a mosquito almost certainly kills a bee. Even if you apply these chemicals to a separate area of your yard, they have a high potential of running off into the surrounding pollinator friendly areas. Stick to hand weeding problem plants whenever possible and try handling pesky insects in chemical-free ways like limiting standing water or having nests removed.

5. Mow remaining lawn infrequently

Conventional turf lawns are fun play spaces, but monocultures of grass do not support pollinators, so it’s always best to limit the amount of lawn on your property. For any lawn that you keep around, one of the most impactful things you can do is to mow as little as possible. Even going from mowing weekly to mowing every other week leads to dramatic increases in the number of pollinators and flowers found in lawns. You don’t need to let the lawn look truly wild to achieve big benefits either! Leaving a margin of unmowed grass around the edge can provide valuable nesting habitat for bees and low-growing flowers like white clover.

By mowing your lawn less frequently, you can support native pollinators like bicolored striped sweat bees Agapostemon virescens!

Following these simple steps can help you take big strides towards making your patch of the urban landscape a haven for pollinators. One of the most rewarding things about implementing steps like these is that you are nearly guaranteed to see returns after just a small amount of investment–if you plant it, the bees, butterflies, wasps, and hover flies really will come. Happy gardening!

To learn more, check out our publication on pollinator gardening produced in collaboration with Tufts CREATE Climate Solutions.

The strange sex lives of bees

By Isaac Weinberg

Most complex organisms, like humans, reproduce sexually. Sexual reproduction occurs when a sperm cell produced by a male fertilizes an egg cell produced by a female. Some organisms, like aphids, can reproduce asexually by undergoing a process known as parthenogenesis, where unfertilized eggs develop into fully functional organisms. Bees ants and wasps, however, reproduce using a combination of both strategies.

These closely related species, known as hymenopterans, must use both reproductive strategies because of their unique genetics. In most complex organisms, even those who reproduce using parthenogenesis, all individuals are diploid and have two sets of chromosomes. In hymenopterans, however, females are diploid and males are haploid, having only one set of chromosomes. Females arise from fertilized eggs, while males arise from unfertilized eggs. This unique sexual determination is called haplodiploidy. It is possible because the queen can selectively fertilize any egg she lays, and as such can determine whether each egg will develop into a male or a female.

Haplodiploidy is even weirder than it sounds because of the effects it has on each bee’s family tree. Every female bee develops following normal fertilization, and as such has a mother and a father. Male bees, known as drones, do not have a father, and receive 100% of their genetic code from their mothers. This in turn means that each female bee has two grandmothers, but only a single grandfather! Male bees not only have half the genetic material of their female counterparts, but are also less prevalent in the family tree!

This brings us to another quirk of haplodiploid reproduction. In sexually reproducing species, both sperm and egg cells are haploid. Both of these cell types are created through meiosis, a process by which diploid cells undergo a complex multistage reductional division. In hymenopterans, meiosis only occurs in female bees as the queen generates her eggs. Since drones are already haploid, their sperm cells do not need to undergo meiosis. Instead, each sperm cell contains an exact copy of the drone’s complete genome.

Where does the meiosis that generates those sperm cells occur? Within the queen as the egg that develops into a drone is produced! Putting all the pieces together, each drone is haploid, receives all its genetic material from a single parent, and is produced through meiosis. All features of a sperm cell in a species that reproduces using classical reproduction.

What is a sperm cell’s only purpose? Fertilization. Each drone leaves the nest in hope of finding a mate to pass his genes onto the next generation. If successful, each of his daughters will have inherited his complete genetic code – and will be equally related to his mother as to their own. His sons will inherit… nothing. Since each male is produced from an unfertilized egg, drones cannot have sons. The next time you see a drone sipping nectar from a flower, remember that his only purpose in life is to carry and pass on his mother’s genes to a new generation of daughters–some of whom will be future queens of their own colonies.