Wednesday, March 31, 2010

Gardens for Bumblebees

My good colleague, Maria Kasstan spoke to the Toronto Beekeepers' Cooperative last evening. She had just returned from attending the annual pollination symposium in Guelph. The City of Guelph, Ontario, it turns out, has a very active, city-wide pollinator awareness program. A rallying point for all of this activity is Pollination Guelph, sponsor of the symposium.

Now Guelph has for many decades been home to the Ontario Agricultural College and Guelph University. Lots of bee people work there, with plenty of interest in pollination biology. But that doesn't quite explain it all. An enthusiasm for pollination and pollinator-friendly gardens in Guelph seems to extend through the city council and many branches of city government as well.

Maria kindly gave us a capsule account of what she learned. Her talk was fascinating, especially for someone interested in bumblebees.

Bumblebees, in particular, were mentioned during the symposium, including news of the recent promising sighting of the Rusty-patched Bumblebee in Ontario's Pinery Provincial Park. Also discussed was the relationship between arctic bumblebees on Ellesmere Island and the flowers they visit. Apparently the corolla of the flower serves as a parabolic reflector to concentrate the sun's warming rays. So in that chilly climate, bumblebees visit the flower to keep warm, effecting pollination at the same time.

But the big topic of the day was how to develop gardens that serve as habitat not only for bumblebees, but for all insect pollinators. The City of Guelph, under its Healthy Landscapes program publishes lists of pollinator friendly plants to include in the garden. They cover bee, butterfly and hummingbird plants, sun and shade tolerant native plants, as well as trees and shrubs that provide pollinator resources.

The guidelines for pollinator gardens include:
  • plant plenty of nectar and pollen rich flowers
  • provide food sources (host plants) and overwintering places for eggs and pupae
  • provide water
  • avoid using pesticides and herbicides
  • provide sites and materials for nesting and overwintering
  • reduce your area of lawn grass

Because of monoculture and pesticide use, agricultural areas provide no comfort for bumblebees. So what we do in our cities and in our own gardens may be the best hope for bumblebee conservation.

[Photo by Jina Lee, CC License]

Sunday, March 28, 2010

The Fly and the Bumblebee: Not a Love Story

The Toronto Entomologists' Association invites some great speakers. Yesterday we were treated to nine grad student presentations on topics ranging from the identification of syrphid fly pollinators to the diversity of aquatic invertebrates. Especially, it seemed, there's an awful lot of fly research going on in southern Ontario.

Most interesting to me was a paper given by Joel Gibson of Carleton University on the fly family Conopidae, some members of which are parasitic on bumblebees. Actually the technical term for these Thick-headed Flies is parasitoids. A parasitoid is any parasite that spends an extended time in the body of its host and is so large that as it grows it ultimately kills that host. Parasitoids, you could say, are parasites that are rather more like predators than like ordinary parasites.

Right: A conopid fly of the genus Physocephala, known to be parasitoids of bumblebees. Note that unlike most flies, the antennae are quite long, making it a more effective wasp mimic.

Adult Thick-headed Flies are rather elegant-looking creatures, with a slim, wasp-like body and black-and-yellow waspish colors. They visit flowers where they feed on nectar.

And it is presumably around flowers where they encounter unsuspecting bumblebees. The fly is said to be able to alight on the flying bumblebee and deposit an egg into its body. When the fly larva hatches, it burrows deep into its host and begins to feed on the bumblebee's tissues.

In some areas, we were told, 40% to 50% of the bumblebees are carrying conopid larval parasitoids. The infected bees become feeble and unable to fly. They may be found walking on the ground, their abdomens swollen by the mature fly larva that has consumed most of their internal organs. Eventually the bee dies and the Thick-headed Fly larva pupates inside.

Thick-headed Fly parasitoids are yet another pressure on bumblebee populations. The fly is, no-doubt, something that bumblebees have evolved to cope with over time. But when combined with habitat destruction and widespread pesticide use, this highly effective parasitoid is just one more potentially dangerous stressor.

[Photo by James Lindsey, CC license]

Friday, March 26, 2010

Bumblebees and Climate Change

Bumblebees can now be spotted all year round in southern England (Read more here).

Yes, British Winters are still cold, but not as cold apparently, as they used to be. Bumblebees are hardy anyway, and can continue to fly in search of food at colder temperatures than most other pollinators. Besides, in British gardens there are apparently some cultivated plants that bloom during the Winter months, so the bee food supply is continuous.

Right: The Buff-tailed Bumblebee, a British species seen in very early Spring.

Bumblebees in temperate climates usually escape winter as part of their annual colony life cycle. Normally it is only the fertilized queen that overwinters. In the Fall, she chooses a sheltered spot, often in a shallow burrow in the soil. There she waits until winter has passed and Spring flowers promise a fresh supply of nectar and pollen.

The queen begins a new colony first by finding an abandoned mouse nest or other suitable cavity, often underground. She gathers nectar and pollen to nourish the larvae that develop from the eggs she lays. When her first brood of worker bees emerge as adults, they take over the job of gathering food, leaving the queen to the tasks of laying eggs and maintaining order in the colony.

By mid- to late-Summer, the bumblebee colony starts to produce sexually active males and queens. When these new queens have mated, they are the ones who normally overwinter and begin the next generation. The old queen and the remaining workers and drones usually die when they can no longer find enough food and the first heavy frosts overtake them.

These observations of Winter-active bumblebees in southern England raise some intriguing questions. Are they mated queens that just don't bother to hibernate? Or are they workers and males left over from the previous summer who can still find enough food to survive? If the latter, do last year's workers and males become competitors with the new queens for scarce Spring food resources?

Dave Goulson's observations suggest that mated queens of Bombus terrestris in southern England just go ahead and found a new nest, not bothering to hibernate first. But if they were to start simply laying eggs in their maternal colony, this would seem to put the species well on the way towards continuous, immortal colonies, like those of honey bees.

As with all of the many changes that have occurred in Earth's environment during past millenia, those bumblebees that can adapt gracefully will survive and prosper. Those that cannot adapt will become just another chapter in bumblebee history.

[Photo of B. terrestris from the Wikimedia Commons, CC License]

Wednesday, March 24, 2010

A Hopeful Sign?

The Rusty-patched Bumblebee (RPB) seems to have been a casualty. The Xerces Society, a not-for-profit organization that specializes in the protection of invertebrate animals and their habitat, has identified the Rusty-patched as one of four North American bumblebees that have experienced serious decline in the last 50 years. This RPB is one of the prime examples of why bumblebees need our help.

Right: Color pattern diagrams for workers of the Rusty-patched Bumblebee (Bombus affinis)

The RPB was formerly widely distributed in eastern and central North America. It is represented by specimens in historical insect collections from southern Ontario and Quebec in Canada, and all the way from Minnesota across to Maine in the northern U. S. It also occurred in a wide swath down the eastern part of the continent, as far south as Georgia. Today it has disappeared almost entirely from that entire broad range.

A recent study by bee researchers, Sheila Colla and Laurence Packer has provided quantitative evidence for the decline of the RPB. They collected intensively in two locations where RPB was formerly found over a period of three years. They were completely unable to locate the species in its former haunts. Broader collecting throughout most of the former range turned up only one remaining stand of the species in southern Ontario.

Fortunately, last year, the missing species was also sighted by biologist Liz Day in Indiana. This has to be a hopeful sign.

You can help. The Xerces Society would like everyone to be on the watch for the Rusty-patched Bumblebee. If you want to learn how to spot, they have information and even an identification guide on their site. You can see more photos of the species HERE, HERE and HERE.

There may still be hope for the Rusty-patched Bumblebee. Let's try and give all bumblebees a better chance by protecting their habitat and planting more bee-friendly flowers.

Maybe one day we'll see the RPB flashing its brown patch among the blossoms in our gardens once again.

Sunday, March 21, 2010

Bee Degree Days

In addition to avoiding each other, emerging bumblebee queens need to be out and flying around when their favorite early food plants are blooming. Too early and it's too cool, with no nectar or pollen. Too late, and the blooming period is over, the preferred food all gone.

How do they do it? How do they figure out when to emerge, especially underground, or buried in a rotten log, where the sun doesn't shine to let them know the days are getting longer?

Bumblebees can apparently tell when to emerge the same way biologists can predict the dates for Spring plants to flower - they use growing degree days.

Biologists have found that Spring flowers bloom after their buds have received enough heat. During the depths of winter, no bud development happens at all. But in late Winter and early Spring, the days start to get warmer. Every day the temperature is above approximately 50 degrees F, the flower bud grows and develops a bit more. Finally, when there have been enough hours warm enough for growth, development is complete and the blossom unfolds.

We know it's accumulated warming that makes the difference, because if it was just the increasing daylength, Spring flowers would bloom on the same date each year. They don't. They bloom earlier in a warm Spring and later in a cool one.

It turns out you can calculate the amount of heat a Spring flowering plant is receiving using a measure called degree days. You add up all the hours since January 1st that the air temperature has been above 50 degrees F and divide by 24 to get a measure called a growing degree day. But since we're interested in bumblebees, we'll call them bee degree days. You can read more about degree days and how to calculate them HERE and HERE.

So if we, or the bumblebee, can keep track of the number of bee degree days, we can predict when the flowers will appear. Each species of flowering plant seems to have its own, unique required number of degree days for blossoming.

Hibernating bumblebees, of course, do not use computers and trig functions to calculate bee degree days. In all likelihood, some aspect of their internal body chemistry changes slowly when the temperature is warm enough. After enough warm days, the chemistry has changed enough to wake up the slumbering queen.

Soon she's on her way, in search of that first, quick pick-me-up of fresh Spring nectar.

[Photo by Tony Wills, CC License]

Friday, March 19, 2010

Bumblebee Mating

Not exactly seasonal, but I wanted to show you this photo, sent to me by a friend, of Common Eastern Bumblebees (Bombus impatiens) mating last Fall.

The queen is the larger individual, clinging to the edge of a leaf, and the considerably smaller male is hanging below her.

By mid- to late summer, new virgin queen and male bumblebees are produced from successful colonies. These individuals leave the nest and seek each other out for purposes of reproduction.

Mate seeking in bumblebees was first recorded by Charles Darwin who set his children the task of following male bumblebees in his garden to record their behavior. The males of most species patrol a route which they mark with scent produced by their labial glands. The pheromone is deposited on "leaves, prominent stones, fence posts or tree trunks" according to Dave Goulson in his book, 'Bumblebees: Behaviour, Biology and Conservation'. It's not certain exactly how the newly emerged queen encounters the patrolling male. Presumably a combination of the species specific pheromone used for marking and the height above ground of the male's patrolling route provides the appropriate cue.

Observations are few, but presumably the male and female make contact in the air. Then, shortly after coupling, they alight until copulation is complete.

[Photo by Michelle Arsenault]

Monday, March 15, 2010

Queens Spring Into Action

Spring is the time for hope and for creating new life. But Spring can be the most dangerous period of the year for bumblebees.

We'll be seeing bumblebees on the wing soon (our colleagues in England are seeing them already), for Spring is when mated queens emerge from hibernation. Each has overwintered in a shallow burrow in the soil. Energized by the warming rays of the sun, each queen must crawl to the surface and fly off in search of a first meal of nectar to fuel the colony founding tasks that lie ahead.

But what if an unusually cold winter or Spring rains that flood the soil kill off most of the hibernators? What if there are no blossoms to forage after they emerge? What if too many queens have survived and there is not enough nectar to go around?

An uncertain environment and intense competition make each new Spring a challenge. This is why early bumblebee populations may be boom or bust - tens of thousands of queens in some years, few in others.

One strategy that bumblebees appear to have evolved in order to reduce competition for resources each Spring is staggering emergence times. North American bumblebees (like those in any temperate climate) can be characterized as either early-Spring, mid-Spring or late-Spring emergers.

Right: Emergence pattern for 3 common eastern North American bumblebee queens.

Because most wildflowers bloom at different times through the season, early emerging queens have access to a different initial food supply than those emerging later on. The result - more bumblebee species can co-exist in the same community than if they competed head on for every resource.

Friday, March 12, 2010

"Nectar gone. Don't bother"

How do bees, either bumblebees or honey bees, collect nectar and pollen as efficiently as possible? This activity is called foraging, and it is central to the success of any social bee colony.
Honey bee and bumblebee, both foraging on goldenrod

Foraging has been studied best in honey bees, and they are known to use a variety of techniques including aromas, communicating flower location, and scent marking to ensure that individual workers do not waste a lot of time looking for food in unlikely places.

Bumblebees also use scent marking to improve their foraging efficiency. Apparently it works like this. Each bumblebee body is coated with a number of chemicals that serve to waterproof its exoskeleton. As a bee walks over the surface of a flower collecting nectar and pollen its feet leave traces of these chemicals behind.

The next bee to come along can detect the presence of the chemical marker left by the previous forager using sensory organs in its antennae. Bumblebees can often be seen hovering just in front a flower before deciding to alight or instead to move on to the next blossom. It seems that if the bee finds that another has just been working on the flower, it moves on, knowing that the nectar in that flower has probably been used up.

So bumblebees warn each other off a flower that has little nectar left. And honey bees do the same thing. The chemical markers used by different species are fairly similar, and it seems that bumblebees can recognize the 'no nectar' signal left by honey bees.

This chemical marking behavior is probably why you never seem to see bees fighting over a flower. It's a way to ensure that all of them make the best use of their time in the field.

But it also suggests that if you have a lot of foraging honey bees out there marking flowers with 'no nectar' signs, there may not be much left over for the less abundant bumblebees.

[Honey bee and bumblebee photos by D. Barr]

Wednesday, March 10, 2010

New Bumblebee Sightings in Scotland

Things may be looking up for bumblebees in Scotland. One rare and endangered species for that country, the Great Yellow Bumblebee, was seen farther south last summer than at any time in the past 30 years. This species has been declining for some time in the UK, and populations have been restricted to the far northern highlands and isolated northern islands of Scotland.

A possibly less auspicious sighting came early this year. The Southern Cuckoo Bumblebee (SCB) was spotted near the southern border of Scotland, a new species for the country. Previously the SCB has been common in the UK only near the southern coast of England.

Yes, it's a new bumblebee for Scotland, and a species that seems to be expanding its range rather than being in decline. But is this a good thing for bumblebees as a whole?

The questions arises because cuckoo bumblebees are parasites in the nest of other bumblebees. The normal bumblebee colony lives and grows by harvesting nectar and pollen from flowering plants. Most bumblebees have a number of special adaptations for pollen gathering, the most obvious of which is the presence of a wide, pollen gathering 'basket' on both hind legs.

Cuckoo bumblebees, on the other hand, have no pollen basket and make their living by invading the nests of pollen gathering species. The 'cuckoo' female takes over from the queen of the host species and begins to lay eggs. The workers of the host bumblebee then proceed to rear the cuckoo's eggs as though they were their own sisters. As a result the host colony rears no queens to carry on the next generation. All queens and males produced from that time on belong to the cuckoo species.

So you can see that a new cuckoo bumblebee is a mixed blessing. It can prosper only at the expense of normal bumblebee populations.

The ability to keep track of the gradual changes in UK bumblebee populations is possible largely because of the efforts of organizations like the Bumblebee Conservation Trust. Without a concerted effort to monitor pollinator populations, we are in danger of losing these critical components of our ecosystems before anyone has the chance to take action to save them.

Let's watch those bumblebees.

[The photo above is of the Great Yellow Bumblebee (Bombus distinguendus), taken by James Lindsay and made available under a Creative Commons licence.]

Sunday, March 7, 2010

Which Bumblebee Is That?

This is one of a series of short notes on recognizing commonly seen bumblebees.

Just noticed the great bumblebee illustration on the cover of the book, 'Peterson First Guide to Insects of North America.'

According to Paul Williams' online key, this looks like it ought to be Bombus pensylvanicus, the American Bumblebee. This species can usually be recognized by the single yellow band at the front of the thorax, together with broad yellow bands on the 2nd and 3rd abdominal segments. The individual illustrated has the first abdominal segment all yellow, while many females (queens and workers) of this species have only a narrow yellow band at the back of this segment.

For many of us it seems easier to become familiar with insects that have a common name, like the American Bumblebee, in addition to its latin name (Bombus pensylvanicus). Many North American bumblebees don't seem to have been given common names yet. But here are about 20 exceptions:

Common Eastern Bumblebee - Bombus impatiens
Black and Gold Bumblebee - Bombus auricomus
Rusty Patch(ed) Bumblebee - Bombus affinis
Yellow Banded Bumblebee - Bombus terricola
Southern Plains Bumblebee - Bombus fraternus
Brownbelted Bumblebee - Bombus griseocollis
Redbelted Bumblebee - Bombus rufocinctus
Lemon Cuckoo Bumblebee - Bombus citrinus
Fernald Cuckoo Bumblebee - Bombus fernaldae
Indiscriminate Cuckoo Bumblebee - Bombus insularis
Ashton Cuckoo Bumblebee - Bombus ashtoni
Two-spotted Bumblebee - Bombus bimaculatus
Confusing Bumblebee - Bombus perplexus
Tricolored Bumblebee - Bombus ternarius
Half-black Bumblebee - Bombus vagans
Yellow-faced Bumblebee - Bombus vosnesenskii
Northern Amber Bumblebee - Bombus borealis
Yellow Bumblebee - Bombus fervidus
American Bumblebee - Bombus pensylvanicus
Franklin's Bumblebee - Bombus franklini
Western Bumblebee - Bombus occidentalis
Sanderson Bumblebee - Bombus sandersoni
Variable Cuckoo Bumblebee - Bombus variabilis

You can buy this beginner's insect field guide, with the cover illustration shown above, at

Tuesday, March 2, 2010

Some Other Native Pollinators

Bumblebees are special and unique in many ways. One way in which they are not unique is in being a group of native pollinators. There are also lots of other native insect pollinators, hundreds of different species.

Many of our native pollinators are bees as well, but there are also lots of flies, wasps, butterflies, moths, and beetles that provide pollination services to flowering plants.

Debbie Hadley, who writes about insects for, has provided a nice overview of 10 important native pollinators, all of which happen to be bees. And this is appropriate because of all the insects, bees are the most thoroughly adapted for gathering pollen and transfering it from flower to flower.

To put Debbie's 10 pollinators in context, approximately 17,000 species are from known around the world at present. And those species can be divided into about 7 families. A family is a group of species that have a lot of things in common, things like anatomy, behaviour and ecology. And most bee families differ from each other in appearance, habits and lifestyle.

All this is only to point out that although the bumblebee ways of pollinating plants are very effective, they are by no means the only methods of doing so.

Find out what Debbie Hadley has to say about the ways carpenter bees, mason bees, sweat bees, polyester bees, squash bees, dwarf carpenter bees, leafcutter bees, alkali bees and digger bees. You'll be amazed at how many of these little creatures are helping us out by pollinating our fruit and vegetable crops.

I'm glad bumblebees are the first on Debbie's list. Fortunately, many of the things we can do to support bumblebees, things like planting bee-friendly gardens, will support the rest of the native bees as well. Debbie has also posted a list of 12 things you can do to help native bees.

Bees just love flowers, so we have to give them all we can.

[The photograph is of a mason bee, courtesy of USDA, made available on the Wikimedia Commons and in the public domain.]


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