Archive for July, 2011

Mimics of bumble bees

July 11, 2011

Syrphid fly, Mallota bautias

We think that we know what a bumble bee looks like, but often we are deceived by some very good imitators. There are a number of flies that masquerade as bumble bees despite the fact that they have only two wings, instead of four and that their antennae are significantly shorter. There are even a few moths and beetles that imitate bumble bees.

Syrphid fly, Mallota

Syrphid fly, Eristalis

Flower flies, also called hover flies or Syrphid flies visit flowers frequently and are good imitators of bees or wasps. They lack stingers, but their appearance gives them some protection from hungry birds that fear the sting of a bee and are left alone. Some are specialized to look like bumble bees. This mimicry occurs in other continents, too, with European and American flies mimicking European and American species of bumble bees respectively.

Robber fly

Robber fly, Laphria thoracica

Robber flies are ferocious predators, capable of catching some insects in flight. Among them, there are some that imitate bumble bees so convincingly that they can fool anybody, including experts. In this case, the purpose of the mimicry may be to fool their prey, as well, as their possible predators.

Bee fly, Bombylius. Notice the long tongue

Carpenter bee on swamp milkweed

Some beeflies and also tachinid flies are good mimics of bumble bees.

Carpenter bees also look very much like bumble bees. The main difference is their glossy and almost hairless abdomen, while bumble bees are covered by fuzz all over. In this case the mimicry would benefit both of them.

Cuckoo bumble bee, Bombus citrinus

Curiously enough, some species of bumble bees are mimics of each other, although they may not be closely related. Some of the cuckoo bumble bees seem to be mimics of their hosts, for instance, Bombus citrinus and its host Bombus impatiens.

Bombus impatiens

The mimicry makes it very hard to tell the species of bumble bee apart. The similarity among bumble bee species probably provides them additional protection. Predators need to learn the lesson only once instead of twice. In fact, this kind of mimicry may help the males, also, since they lack stingers.

Bumble bees. Introduction

Beginners Guide to Pollinators and Other Flower Visitors

Bumble bee’s enemies

July 10, 2011

Bombus bimaculatus paralyzed by ambush bug

The life of a pollinator can be quite hazardous. There are plenty of creatures willing to devour one of them, from insects and spiders to birds. In addition to that, there are many parasites and other pathogens. Perhaps the highest mortality comes from the so called parasitoids and cuckoos. Parasitoids behave somewhere between a parasite and a predator; they parasitize the host, feeding on it, and eventually killing it, while predators kill and eat the prey all at once. Cuckoo bees and wasps, just like cuckoo birds take over the nest, lay their eggs and let the workers of the host species take care of the brood. Many cuckoos are related species, mainly other bumble bees; in some cases they mimic the appearance of the host species.

In general, most birds seem to avoid bumble bees; although there are a few species that specialize on bees. Skunks, voles and moles can attack their nests and eat their reserves and grubs. These creatures destroy a good number of nests. There is a story about Darwin saying that the British armies owed a lot to old spinsters. This was his explanation: Old spinsters owned cats which ate field mice. Fewer mice meant that more bumble bee nests survived. In turn, the bumble bees pollinated the alfalfa that fed the cattle that fed the soldiers and kept them strong and healthy. It was just an unproven entertaining hypothesis, but still a nice illustration of the intricate web of life.

Crab spider on thistle

Crab spiders are so called because they look and move like crabs. They are among the most common predators. They build no webs; instead they hide inside blossoms, waiting patiently for prey and ready to pounce on the first flower visitor that comes within reach. They are well camouflaged and are capable of changing their colors if they have to move to another flower.

Ambush bug on multiflora rose blossom

Ambush bugs deserve the name. They sit for long hours, well hidden inside a flower or cluster of small flowers, waiting for flower visitors. Their contour is jagged making it hard to detect them. They are very good at holding still, tucked in between petals. Their front claws look like those of a preying mantis and they have a sharp beak used for stabbing their prey and sucking vital juices. Their venom must be very powerful because they can paralyze a bumble bee twice their size in the blink of an eye.

Conopid fly on common milkweed

Some flies of the Conopidae family parasitize bumble bees. They hang around flowers waiting for bumble bees and lay just one egg in the narrow space between body segments. The egg hatches, the larva gets inside the unfortunate bee and proceeds to feed on its blood, (its real name is hemolymph because it is more similar to lymph than to blood). As it grows it starts eating the tissues, eventually killing the host.

Bee wolf Philanthus gibbosus

Bee wolf wasps attack many types of bees, bumble bees included, and also other insects. They overpower them and take them to their nests to feed their young. They have a very thick, pitted body cover that serves them as armor.

cuckoo bumble bee, Bombus citrinus

Other enemies of bumble bees are bumble bees themselves, the so called cuckoo bumble bees. There are several species of them. They build no colonies, nor have any workers. A queen attacks and subjugates a colony of honest, hard working bumble bees. She usually kills the resident queen and destroys any eggs. Then proceeds to lay eggs of her own which are nurtured by the workers of the host species.

Bumble bees also suffer from many of the pathogens that afflict honey bees, such as mites, fungi, nematode worms, bacteria and viruses. The life of a pollinator is not an easy one.

Bumble bees. Introduction

Beginners Guide to Pollinators and Other Flower Visitors

Bumble bees life cycle

July 9, 2011

With about fifty species in North America it is hard to generalize. However most bumble bees are colonial; there is a queen and workers living together in a hive, with the queen being the mother of all the workers. The colonies can vary in number from no more than a couple of dozens to a few hundreds.

Early in the spring the adult queen that was born and mated the previous season emerges from its wintering place, hidden under bark or in some other safe place. It starts looking for the right place to raise its family. This can be a rodent’s burrow or a similar hole. In some cases just a tussock of grass will do. Once she finds a satisfactory locale she starts redecorating her property, making it more suitable for her babies.

She builds some wax containers, which she fills with food, nectar and pollen and she builds a larger mass or brooding cell, made of a mixture of wax, pollen, nectar and her own saliva. This is where she lays a batch of eggs. For the next two weeks or so, she takes care of this brood by adding more food as needed and by keeping it warm during the night or colder weather. She does this, as brooding birds do, by lying on top of the egg mass. Her belly has even a hairless patch, just like such birds, which helps to transfer the heat from her body to the brooding cell where the growing larvae are.

Bumble bee nest. © Scott Nacko (Bugguide image 421344)

The larvae grow rapidly on that nutritious mixture and soon a half dozen or a dozen adults emerge from this brood. They are smaller than the queen and they are all worker females. They set to work right away taking care of housekeeping and going out for more nectar and pollen. Now the queen doesn’t need to go out and hardly does so from then on. She simply stays home laying more eggs and being attended by the workers.

Worker with a load of pollen

The colony keeps growing and by the fall the queen lays eggs which will become the future queens and also lays some male eggs.

When the new queens emerge, they don’t do any work in the colony. They just go out and mate with males, possibly from another colony. After that they start looking for a safe place where to spend the winter. The old queen, all the workers and the males die shortly afterward.

Bumble bees. Introduction

Beginners Guide to Pollinators and Other Flower Visitors

Bumble bee’s intelligence

July 7, 2011

Honey bees have the reputation of being the Einsteins of the insect world. They have shown remarkable abilities of memory, learning and communications. The more we study them, the more we are amazed at their capabilities.

Honey bees are not the only smart ones, other bees have given us signs of their aptitudes and bumble bees may not be far behind from honey bees in their capacity to remember things important to them and to learn new things when necessary.

Digging deeply into a penstemon blossom

The brainy bumblebee

The brain of a bumblebee is smaller than the proverbial head of a pin; amazingly enough that small amount of gray matter is capable of remarkable feats of memory and learning. That industrious collector of nectar and pollen needs all this brain power to optimize its efforts when collecting such valuable resources. Let us see what it is capable of doing:
She (because it is always a she) can learn how to open flowers of different shapes, can remember such a task when confronted with more flowers of the same kind and can also remember the location of abundant resources such as shrubs with numerous blossoms or clumps of small plants which bloom simultaneously.

How does she do it? How do we know about her learning abilities? Here is what we know. When faced with a new flower, especially one as complicated as a turtlehead or an impatiens, she puzzles about it for a few minutes. She can smell the nectar and knows that it is there somewhere but she finds it hard to reach. After a few tries she begins to get the hang of it and gets her whole, plump, little body inside the flower, sticks her long tongue as far as needed and: success. The second and third flower of the same kind that she visits take less time; by the time she has visited more than ten she has become a pro and goes about her business with remarkable efficiency. Another type of flowers that tests its abilities are those that require buzz pollination (read: Bumble bees as pollinators)

bumble bee visiting a turtlehead

bumble bee visiting a turtlehead

Another proof of her brain power is her capacity to memorize the best business locations, in other words, the bushes or clusters of plants with abundant flowers and plenty of valuable resources. It probably uses a combination of clues to recognize the area: landmarks, the position of the sun, smells, perhaps even the magnetic field of the earth. Bumble bees are not alone in the insect world to perform these deeds. Many other bees and also butterflies and moths have shown these skills. All these little creatures are capable of developing a daily route; they even can memorize the timing of blooming, morning or afternoon and show up right on schedule.

Bumble bees. Introduction

Beginners Guide to Pollinators and Other Flower Visitors

Bumble bees as pollinators

July 6, 2011


Impatient bumble bee and impatiens. It fits like a glove

Bumble bees collect nectar and pollen to feed the babies and that is how they pollinate many flowers. Some are generalists that visit many different kinds of flowers while others are more specialized. The species with longer tongues show a preference for flowers with deeper throats although they can also reach the nectar of flatter flowers. Those with shorter tongues are more limited in their choices. Body size also matters; larger bumble bees may keep the smaller ones from visiting favorite flowers.
buzz pollination

Turtlehead. In and out with great skill

Because of their wide geographic distribution and long season (from spring to fall), they are pollinators of a wide array of wild flowers, as well as some important crops such as tomatoes, eggplants, alfalfa and clover.

One interesting feature of bumble bee pollination is that they can practice the so called buzz pollination, a deed that honey bees never mastered. Some flowers don’t have ready available pollen; instead they keep it inside the anthers. Only a pore at the tip of the anther allows the pollen to escape. For that it is necessary to shake the anther, just like a saltshaker. Bumble bees and a number of native bees are pros at this shaking. They use their flight muscles to cause a vibration, easily heard if you are near. Plants in the tomato family, such as tomatoes, peppers, eggplants, and members of the Ericaceae family, such as azaleas and rhododendrons, blueberries, cranberries and a few other berries, require this form of pollination.

Buzz pollination of azaleas. Notice the buzzing sound

Bumble bees. Introduction

Buzz pollination of Senna

Beginners Guide to Pollinators and Other Flower Visitors

Bumble bees: the pandas of the insect world? Part III

July 5, 2011


Bumble bees are almost cosmopolitan. They are more abundant and represented by a larger number of species in the northern hemisphere, especially in temperate zones. They prefer relatively drier climates.

Originally they were absent only in Antarctica, Australia and New Zealand. But in the last century they were introduced in New Zealand to help with alfalfa pollination. Attempts to introduce them to Australia years ago failed. Nowadays, green house tomato growers are pressing for permission to import European bumble bees; but they face strong opposition from those who oppose the entry of alien species. Recently bumble bees became established in Tasmania, after making their way there, either illegally or accidentally. There is strong surveillance to prevent the species from entering the mainland, but occasionally a bumble bee queen makes its way there. Perhaps it is just a matter of time.

In North America there are approximately fifty species. Some can prosper in a wide range of habitats others are more limited. Some are found only in the West Coast, others in the East. There are northern and southern species, for instance the tricolored bumble bee is mostly a northern species, seldom found south of Pennsylvania. There is a species, the polar bumblebee or Bombus polaris, found within the Arctic Circle; it takes full advantage of the explosion of little flowers that occurs in such latitudes through a very brief period. In that short time it has to raise a family and complete its full life cycle. This species has only small colonies. Other bumble bees do well in arid regions or at fairly high elevations.

Bumble bees can be found in farms, in suburban gardens and even in cities. Anywhere that flowers bloom, it is likely that there are bumble bees. The most serious limitation to their existence in cities is the lack of appropriate nesting sites; however some hardy souls manage to prosper in the concrete jungle.

Sadly, there are signs that not everything is well with bumble bees populations. Despite our limited knowledge, there are some evidences of declines, maybe even extinctions, of some populations. In England, where bumble bees are better studied than in the United States, there is clear evidence of the loss of some populations of bumble bees. There are even two species that are believed extinct in Great Britain, although the same species are still represented in the continent.

Bumble bees. Introduction

Beginners Guide to Pollinators and Other Flower Visitors