Mysterious Bumble Bee Behavior

On a cool day in early November, my husband spotted a cluster of Bumble Bees on Blue Wood Aster (Symphyotrichum cordifolium) in the garden outside our living room window.  A queen bee was at the center of the group.  She was clinging to a flower, with as many as four other bees grasping her.  Amazingly, the queen was supporting the weight of the entire group.

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens)) on Blue Wood Aster (Symphyotrichum cordifolium)

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens)) on Blue Wood Aster (Symphyotrichum cordifolium)

We watched for about an hour.  During that time the number of bees clutching the queen varied a bit as some of the bees came and went.

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens) on Blue Wood Aster (Symphyotrichum cordifolium)

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens) on Blue Wood Aster (Symphyotrichum cordifolium)

It was a puzzle trying to figure out what was going on. Since the temperatures were fairly low, could they just be huddling together for warmth?

Later, when I looked at the photos I had taken, an explanation for their behavior presented itself. The smaller bees appeared to be males, one actively mating with the queen, with the others doggedly hoping for their turn.  (A bunch of hangers-on and wanna-bees. Sorry!)

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens), one mating with the queen.

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens), one mating with the queen.

In the Bumble Bee world, the only females that mate are queens. The primary role of male Bumble Bees is to pass on their genes if chosen by a queen for a chance to mate.  Queen Bumble Bees decide who their mating partners will be.  When a queen is ready she’ll chose the lucky male that will be the recipient of this honor.

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens), one mating with the queen.

Bumble Bees (probably Common Eastern Bumble Bees (Bombus impatiens), one mating with the queen.

This gathering may have been the male bees’ last chance to pass on their genes. The males, any non-breeding females and the old queen from a colony will die as the cold winter temperatures set in.

Only newly emerged queen Bumble Bees survive through the winter. Soon after successful mating, this new queen will seek an underground winter hibernation shelter. If she survives the stresses of winter, she will be among the first bees we see next spring, foraging on spring ephemerals.  She’ll look for a nest site, provision it with nectar and pollen, and begin laying eggs for the new Bumble Bee generation.

Queen Bumble Bee in spring on Virginia Bluebells (Mertensia virginica).

Queen Bumble Bee in spring on Virginia Bluebells (Mertensia virginica).

 

Acknowledgements

Thanks to Dr. Randi Eickel of Toadshade Wildflower Farm for help identifying the bees and their behavior.

Thanks to Jeff Worthington for ‘wanna-bees’.

Resources

Goulson, Dave. A Sting in the Tale.  2015.

Heinrich, Bernd. Bumblebee Economics.  2004.

Colla, Sheila; Richardson, Leif; Williams, Paul. Bumble Bees of the Eastern United States.  2011.

Bumblebee Conservation Trust – The Bumblebee Lifecycle

 

 

 

Feasting on Green-headed Coneflower

How many flowers do you see in the photo below?

Gray Hairstreak on Green-headed Coneflower (Rudbeckia laciniata)

Gray Hairstreak on Green-headed Coneflower (Rudbeckia laciniata)

If you said one, that’s the answer I was looking for. However, it’s not correct!

The plant pictured here is Green-headed Coneflower (Rudbeckia laciniata), also sometimes called Cut-leaf Coneflower in deference to its deeply lobed leaves.  Green-headed Coneflower is a member of the Aster, or ‘Composite’ family, a name that’s pretty descriptive of their typical flower clusters (inflorescences). What our brains think is a single flower is actually a cluster (or composite) of tiny flowers, often of two different types, ray flowers and disk flowers. The petal-like parts of the flower cluster are each an individual ray flower with a single petal. In the center there are dozens of tiny tubular flowers called disk flowers, in reference to the disk-like shape of the flower cluster.  In the picture above, just a few of the disk flowers are blooming.

Some Aster family members just have ray flowers, like Dandelions.

Eastern-Tailed Blue nectaring on a Dandelion

Eastern-Tailed Blue nectaring on a Dandelion

Some have just disk flowers, like New York Ironweed.

Bumble Bee on New York Ironweed

Bumble Bee on New York Ironweed

Many, like Green-headed Coneflower, have both types of flowers. When both ray flowers and disk flowers are present, the ray flowers are often sterile, in which case their primary purpose is to act as nectar guides, alerting pollinators to the availability of nectar and pollen in the many disk flowers at the center of the flower cluster.

A Silver-spotted Skipper is nectaring on the disk flowers that are in bloom on this Green-headed Coneflower. The lowest disk flowers have finished blooming, while those at the top of the flower cluster are still in bud.

A Silver-spotted Skipper is nectaring on the disk flowers that are in bloom on this Green-headed Coneflower. The lowest disk flowers have finished blooming, while those at the top of the flower cluster are still in bud.

The disk flowers bloom gradually over a period of a few weeks, maximizing the plant’s chances for pollination with the assistance of insect partners. In the case of Green-headed Coneflower, the disk flowers bloom gradually from the bottom, or outside ring, to the top, or center, of the flower cluster.

A Red-banded Hairstreak is drinking nectar from the last few blooming flowers of this Green-headed Coneflower inflorescence.

A Red-banded Hairstreak is drinking nectar from the last few blooming flowers of this Green-headed Coneflower inflorescence.

Because of the number and size of its disk flowers, Green-headed Coneflower is able to attract many insects as potential pollinators. Often multiple insects can be found feeding simultaneously on different flowers in the same flower cluster.

This Green-headed Coneflower offers enough flowers with nectar to feed both an American Copper and a Honey Bee.

This Green-headed Coneflower offers enough flowers with nectar to feed both an American Copper and a Honey Bee.

Green-headed Coneflower’s disk flowers are large enough to accommodate small to medium sized butterflies like those pictured here.  They may rub against some pollen and transfer it to another plant, assisting with pollination.

Summer Azure with Green-headed Coneflower (Rudbeckia laciniata)

Summer Azure with Green-headed Coneflower (Rudbeckia laciniata)

Common Buckeye and Bumble Bee feeding on Green-headed Coneflower (Rudbeckia laciniata)

Common Buckeye and Bumble Bee feeding on Green-headed Coneflower (Rudbeckia laciniata)

Beneficial predators like the thread-waisted wasps (a species of Sphecid wasp) pictured below also benefit from the abundant nectar, giving them the energy they need to reproduce.  (I often see this species mating and nectaring at the same time, as they are doing here. A level of skill and coordination to which humans can only aspire!)  Their anatomy makes it more likely that they will help with pollination than butterflies, since more of their bodies are likely to come in contact with pollen.  The female wasps of this species (Eremnophila aureonotata) hunt caterpillars to feed their larvae.

Green-headed Coneflower with mating Wasps (Eremnophila aureonotata)

Green-headed Coneflower with mating Wasps (Eremnophila aureonotata)

But bees are the most likely to be successful pollinators, because they are the best anatomical match for gathering pollen, and it’s more likely to stick to the branched hair on their bodies and be carried away to be deposited on another flower.

Bumble Bee and American Copper nectaring on Green-headed Coneflower (Rudbeckia laciniata)

Bumble Bee and American Copper nectaring on Green-headed Coneflower (Rudbeckia laciniata)

Sweat Bee on Green-headed Coneflower (Rudbeckia laciniata)

Sweat Bee on Green-headed Coneflower (Rudbeckia laciniata)

The Sweat Bee below is gathering pollen on her hind legs to take back to feed her larvae.  Only female bees gather pollen this way.

Sweat Bee (Lasioglossum species) on Green-headed Coneflower (Rudbeckia laciniata)

Sweat Bee (Lasioglossum species) on Green-headed Coneflower (Rudbeckia laciniata)

Dining on Green-headed Coneflower is not without danger, as this Bumble Bee found out when it fell victim to a Wheel Bug, a type of assassin bug.  Sometimes the diner becomes the dinner.

Wheel Bug (Arilus cristatus) consuming a Bumble Bee smoothie

Wheel Bug (Arilus cristatus) consuming a Bumble Bee smoothie

If the flowers are successfully pollinated, you’re likely to see Goldfinches and other birds feeding on the seeds later in the season and throughout fall.

Goldfinch eating Green-Headed Coneflower seeds

Goldfinch eating Green-Headed Coneflower seeds

The Aster family is the second largest family of flowering plants in terms of its number of species, second only to the Orchid family.  In late summer and fall the Aster family represents a high percentage of what’s in bloom.  For information on a few other Aster family members, see Asters Yield a Treasure Trove! and Fall Allergies?  Don’t Blame Goldenrod!

Resources

Eaton, Eric R.; Kauffman, Ken.  Kaufman Field Guide to Insects of North America.  2007.

Elpel, Thomas J.  Botany in a Day.  2006.

 

Milkweed – It’s Not Just for Monarchs

One of the most well known associations between an animal and plant species is the relationship between Monarch butterflies and Milkweed.  Monarch butterflies may certainly be seen nectaring at various species of milkweeds…

Monarch nectaring on Common Milkweed (Asclepias syriaca)

Monarch nectaring on Common Milkweed (Asclepias syriaca)

Monarch nectaring on Butterflyweed (Asclepias tuberosa)

Monarch nectaring on Butterflyweed (Asclepias tuberosa)

Monarch nectaring on Swamp Milkweed (Asclepias incarnata)

Monarch nectaring on Swamp Milkweed (Asclepias incarnata)

but this isn’t unique – they also drink at a wide variety of other flower species.

Monarch nectaring on New York Ironweed (Vernonia noveboracensis)

Monarch nectaring on New York Ironweed (Vernonia noveboracensis)

It’s the dependency that Monarchs have on Milkweeds as the only food source for their caterpillars that makes this relationship so noteworthy. Monarchs, like many species of insects, have evolved to specialize in their larval (in this case caterpillar) food source in order to gain protection from predators through the chemicals they ingest from the plants they eat. Milkweeds contain cardiac glycosides, which are toxic to many species of birds and mammals. Plants have evolved these chemicals to protect themselves from being eaten, a strategy that has largely been successful for the plants. Plants are all about surviving and reproducing, to further the continued existence of their species.

Such a plan for protection is never completely foolproof, however. Monarchs, along with some other insect species, have evolved to be able to digest these plants and sequester the toxins in their bodies, making the insect unpalatable at best and toxic at worst to anyone inexperienced enough to attempt to eat them. As a reminder to bird or mammal predators who sample such an insect and survive to eat another meal, insects with these toxins have also evolved to have bright warning colors, an easy to remember signal to predators to beware before attempting such a meal again. In exchange for this protection obtained from eating Milkweeds, Monarchs are gambling that this food source will continue to be available. Without it, Monarchs won’t survive.

Monarch Caterpiller on Common Milkweed (Asclepias syriaca)

Monarch Caterpiller on Common Milkweed (Asclepias syriaca)

Monarch Caterpiller on Swamp Milkweed (Asclepias incarnata)

Monarch Caterpiller on Swamp Milkweed (Asclepias incarnata)

Butterflyweed (Asclepias tuberosa) with Monarch Caterpiller

Butterflyweed (Asclepias tuberosa) with Monarch Caterpiller

Monarchs are not alone in their use of Milkweeds. Their copious nectar offerings attract a broad range of butterflies to drink at their flowers, from Eastern Tiger Swallowtails,

Eastern Tiger Swallowtail and Bumble Bee on Common Milkweed (Asclepias syriaca)

Eastern Tiger Swallowtail and Bumble Bee on Common Milkweed (Asclepias syriaca)

to the smallest skippers.

Least Skipper on Common Milkweed (Asclepias syriaca)

Least Skipper on Common Milkweed (Asclepias syriaca)

Swamp Milkweed (Asclepias incarnata)

Tawny-edged Skipper on Swamp Milkweed (Asclepias incarnata)

Tawny-edged Skipper on Swamp Milkweed (Asclepias incarnata)

and Butterflyweed (Asclepias tuberosa)

Sleepy Orange and Andrena bee on Butterflyweed (Asclepias tuberosa)

Sleepy Orange and Andrena bee on Butterflyweed (Asclepias tuberosa)

as well as other milkweed species are also favorites of butterflies, bees, and other insects that are nectar feeders, for their reliable, sweet, high energy food.

Butterflies benefit from the food offered by milkweeds, and in return they do help the plants with pollination, but they are not the most successful pollinators of milkweeds. Milkweeds have bundles of pollen, called pollinia, that are linked in pairs by a thin filament. This connector snags an insect appendage that is inserted in just the right spot in a flower. An insect has to approach the flower in a way that will engage the filament connecting the pollinia, and it must also be robust enough to remove the pollinia from the flower in order to assist the plant in cross pollination. The pollinia is carried by the insect to another flower, and inserted by the same mechanism.

Take a look at the Eastern Comma below. It’s perched on top of a flower, using its straw-like proboscis to sip nectar from a Common Milkweed (Asclepias syriaca) flower. With this approach, a butterfly isn’t that likely to be helping this Milkweed out with pollination.

Eastern Comma on Common Milkweed (Asclepias syriaca)

Eastern Comma on Common Milkweed (Asclepias syriaca)

This Bumble Bee, on the other hand, is facing the flower, with its left front leg inserted in the very location where the pollinia are stored. This bee is engaging the pollen sacs, and has the heft to be able to escape from the flower with them clinging to its leg.

Bumble Bee engaging pollinia of Common Milkweed (Asclepias syriaca)

Bumble Bee engaging pollinia of Common Milkweed (Asclepias syriaca)

If you look carefully at the bee’s left front leg in the photo below, you can see the yellow pollinia attached to it.

Bumble Bee with pollinia of Common Milkweed (Asclepias syriaca)

Bumble Bee with pollinia of Common Milkweed (Asclepias syriaca)

Large bees, such as Bumble Bees and Carpenter Bees, are among the most successful intermediaries in Milkweed pollination. Common Milkweed flowers release a potent fragrance to attract bees to assist them in their reproduction.

Many other insects take advantage of the nectar bounty offered by Milkweeds, including the Snowberry Clearwing Moth (Hemaris diffinis).

Snowberry Clearwing Moth (Hemaris diffinis) and Oleander Aphids (Aphis nerii) on Swamp Milkweed (Asclepias incarnata)

Snowberry Clearwing Moth (Hemaris diffinis) and Oleander Aphids (Aphis nerii) on Swamp Milkweed (Asclepias incarnata)

There’s another insect species dining on this Swamp Milkweed. Do you see the little yellow critters on the stem? You might be thinking, “Eeuuw! Aphids!” If so, you would be half right. These are Oleander Aphids (Aphis nerii), a species frequently found on Milkweeds. But you might want to re-think the “Eeuuw!” It turns out that aphids are an important part of the food chain.

Aphids rarely really harm a plant.  And they offer a sustainable food source in the form of honeydew, a sweet excrement that ants love. The ants protect aphids in exchange for this tasty meal. Ants are essential for aerating soil, decomposing plant matter, dispersing seeds, and in some cases protecting plants from other predators.

Ants tending aphids on Common Milkweed (Asclepias syriaca)

Ants tending aphids on Common Milkweed (Asclepias syriaca)

Aphids are also a food source for other insects. In the photo below, this Oleander Aphid is being parasitized by two predators at once! It’s being bitten in the butt (abdomen) by a Convergent Lady Beetle (Hippodamia convergens) larva, who plans to consume the aphid. Notice also the bulge on the lower left side of the aphid. That is likely the result of a braconid wasp parasitizing the aphid. The adult female wasp lays an egg inside the aphid, with its resulting offspring consuming the aphid from the inside, leaving an empty husk.  (There’s a white squiggly thing on the lady beetle larva that I’m guessing may also be a predator, but so far I haven’t identified it.  If you know what it is, let me know!)

Lady Beetle larvae biting aphid that shows signs (bubble) of being parasitized by a braconid wasp.

Lady Beetle larvae biting aphid that shows signs (bubble) of being parasitized by a braconid wasp.

If you’re really observant you may have noticed that this scene was taking place on half of a Common Milkweed leaf, with the right side of the leaf missing. Wondering how that happened?  It’s the way Milkweed Tussock Moth (Euchaetes egle) caterpillars feed, neatly chewing side by side, stopping at the midrib.

Milkweed Tussock Moth (Euchaetes egle) Caterpillers

Milkweed Tussock Moth (Euchaetes egle) Caterpillers

Another insect that feeds on milkweed leaves is the Red Milkweed Beetle (Tetraopes tetraophthalmus). This clever creature bites through the midrib of the leaf in a few spots near the leaf tip. This stops the milky latex-like sap from flowing to that part of the leaf, making it possible for the beetle to eat it without having its mouthparts glued together by the sticky substance.

Red Milkweed Beetle (Tetraopes tetraophthalmus) on Common Milkweed

Red Milkweed Beetle (Tetraopes tetraophthalmus) on Common Milkweed

Even Milkweed seeds are a source of food for insects like the Small (Lygaeus kalmii) and Large (Oncopeltus fasciatus) Milkweed Bugs.  Adults may also consume nectar.

Swamp Milkweed with Large Milkweed Bugs (Oncopeltus fasciatus) , adults and nymphs

Swamp Milkweed with Large Milkweed Bugs (Oncopeltus fasciatus) , adults and nymphs

Small Milkweed Bug (Lygaeus kalmii) on Butterflyweed (Asclepias tuberosa)

Small Milkweed Bug (Lygaeus kalmii) on Butterflyweed (Asclepias tuberosa)

All of these insects sport bright colors that warn birds and mammals to avoid eating them. Insect and arthropod predators including the Lady Beetles, wasps, assassin bugs, spiders and Praying Mantises (or Mantids) are not put off, however. They may consume not just nectar feeders, but foliage and seed feeders, too.

Assassin Bug (Pselliopus cinctus) and Bumble Bee on Swamp Milkweed (Asclepias incarnata)

Assassin Bug (Pselliopus cinctus) and Bumble Bee on Swamp Milkweed (Asclepias incarnata)

Many of these predators are safe for birds and other predators to eat.  A large percentage of a bird’s diet consists of insects, especially when they are raising their young.

Female Indigo Bunting with lunch

Female Indigo Bunting with lunch

Birds also benefit from Milkweeds by using them as nesting material. The fluffy hairs attached to the seeds can make a soft lining for a Goldfinch nest.

Common Milkweed (Asclepias syriaca) dispersing seeds

Common Milkweed (Asclepias syriaca) dispersing seeds

Most Milkweeds also have strong fibers in their stems that birds use to weave nests, including Northern Orioles

Northern Oriole Nest

Northern Oriole Nest

and Yellow Warblers.

Yellow Warbler

Yellow Warbler

Milkweeds are essential to the continued survival of the Monarch butterfly. They are a copious nectar source for our beleaguered bee populations, and offer food to many other beneficial insects. They’re a source of insect protein and nest material for birds and other animals.  Milkweeds – they’re vital for Monarchs, and a whole host of other species, too.

Butterflyweed with Monarch, Great Spangled Fritillary, and Pearl Crescent

Butterflyweed with Monarch, Great Spangled Fritillary, and Pearl Crescent

Resources

Eastman, John. The Book of Field and Roadside. 2003.

Eastman, John. The Book of Swamp and Bog. 1995.

Eaton, Eric R.; Kauffman, Ken. Kaufman Field Guide to Insects of North America. 2007.

Harrison, Hal H. Eastern Birds’ Nests. 1975

Tallamy, Douglas W. Bringing Nature Home, 2007,

USDA Plants Database