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Saturday, March 9, 2019

Bees and Stingers

Life is hard for pollinators. Well, life is hard for all creatures, not just animals but plants, too. They are all food for other creatures. Leave it to Jonathan Swift to put this concept in a nutshell. He tells us on Poetry, a Rhapsody

...every creature
      Lives in a state of war by nature...”

And explains further:

      “So, naturalists
observe, a flea
      Hath smaller
fleas that on him prey;
      And these have
smaller still to bit'em;
      And so proceed
ad infinitum.”

This is why every creature needs to invest on defenses in order to survive and to pass its genes to the next generation. This is also true of pollinators. We can use bees to illustrate this point, just as Jonathan Swift used fleas. They have a whole array of defenses, some of them we don't even know much about. So let us take a look at the better known one, the stinger.

Bees use their stingers in self defense and in defense of their brood. They don't use them for any other purpose. A stinger is located at the rear end of a bee. It is not like the sharp tongues or jaws of other insects like mosquitoes, horse flies or fleas. These insects use their piercing mouth parts for an entirely different purpose, primarily to obtain nutrition in the form of blood.

Ichneumonid wasps have an impressive appendage
at the rear end, but it isn't a stinger.
It is used only to lay eggs and it is called ovipositor

A stinger has a long and peculiar evolutionary history. Many millions of years ago there were wasps, ancestors of present day wasps and bees, which did not have stingers. They did have a long, pointy tube at the end of the abdomen which they used for laying eggs and got the name of ovipositor. Many wasps still use it for this only purpose. They inject an egg inside the body of another insect, for instance a fat, nutritious caterpillar. The wasp's baby grows surrounded by food and well protected inside the body of its victim. Ordinarily, it ends up killing its host. This is why they are considered something between a parasite and a predator and they are called parasitoids. Their victims are called hosts.

The hosts, in turn, developed defenses against their enemies. Many of the larvae hide themselves inside plant stems or under bark. So the wasps, had to come up with ways to overcome these defenses. Their ovipositors became stronger and longer. Other victims were able to fight back by squirming or biting their attackers back. So the wasps evolved substances that they could inject along with the egg. These substances paralyze the victim without killing it. Thus the progeny has fresh food at its disposal, rather than a decomposing corpse. And here is where the ovipositor took a curious turn.

In some insects it stopped being an ovipositor and became a syringe loaded with toxic stuff. Its function became purely defensive. The wasp found other means to lay her eggs bypassing the stinger. This happened many millions of years ago. All the descendants of those early wasps are what we know as stinging wasps and bees; ants also belong in this category. They all have a modified ovipositor which doesn't serve that purpose anymore.

The stinger took another turn. Bees don't attack prey. Their ancestors used to chase insects that were feeding on flowers. At some point, they discovered that flowers' pollen is so nutritious that it was preferable to feed this to their brood and not bother hunting animal food. In other words, they became vegetarians. However, they did not give up the stinger. They kept it for defense purposes. Obviously, only females have this weapon. Males never had an ovipositor and as a consequence they don't have a stinger either and can't sting you.

A bee's stinger is seldom seen.
It is tucked away at the rear end
One wonders why females have such a formidable defensive weapon while the males don't. The answer seems to be that males are shorter lived. Once they have mated there is no further use for them. The females, on the other hand have to raise a family. They need to defend the nest and the future generation, not just themselves.

I read recently that the budget for defense is bigger than all the other budgets put together, such as all the sciences, arts, education, the environment and so on. How is this possible? Later on, I thought that we are not all that different from the rest of the world, and I mean the entire living world, plants and animals, not just humans.

Thursday, September 21, 2017

A Butterfly's Flashy Colors

Male monarch butterfly
(Danaus plexippus)
© Beatriz Moisset
People fall in love with monarch butterflies because of their bright black and orange pattern. Many monarch enthusiasts are busily raising these butterflies in their gardens and homes. Some have become real experts on these insects and their life cycle. They are profoundly distressed when something goes wrong and one of them fails to make it to adulthood and freedom.

Some particularly despise butterfly enemies. If they catch a predatory bug sucking the juices out of an unfortunate caterpillar, they rage against the predator. Parasitic flies also generate a violent reaction. It is hard to believe, but monarchs owe their beautiful colors to their enemies. Here is the whole story.

Monarchs feed on milkweeds. They are dependent on these plants and cannot digest others. Milkweeds, like many plants produce powerful toxins as a defense against herbivores. These toxins go by the name of cardiac glycosides because they cause heart paralysis. As an additional defense they produce a sticky milky-looking substance that gives them their name. The milk is present in most tissues of the plant and bleed easily, gumming the yaws of a hungry attacker that tries to eat the milkweed plant.

This is enough to deter most plant eaters, but monarch butterfly caterpillars and more than a dozen other creatures have learned to overcome such defenses. Earlier milkweeds, millions of years ago, had milder forms of the toxins. That was all they needed, but some early insects learned to tolerate them and proceeded undeterred to feed from these plants. Thus, milkweeds were forced to create stronger and stronger glycosides and, in turn their feeders found ways to deal with the more powerful toxins. Arms races of this type abound in the natural world.

The monarch butterfly adapted itself to these plants by several means: it avoided the most toxic plants or their most toxic parts; it developed enzymes that could deal with the toxins, or it stored them in parts of its body where they could do no harm. In doing all this, it became dependent on milkweeds. This dependence added a bonus to the monarch's survival, its body is loaded with bad tasting, toxic glycosides, which constitute a powerful defense against its enemies. Most predators avoid the toxic butterfly. However a handful of these predators developed ways to handle the monarch's toxins by eating only the parts with less glycosides, or by evolving enzymes that neutralize these toxic substances. This is another case of the arms race at work.

This is not all. The monarch advertises its toxicity and horrid taste to possible predators. Birds who never saw a monarch butterfly before eagerly take a bite of one. The immediate reaction is that of disgust, spitting up the morsel and shaking their heads or rubbing their beaks in an effort to remove the unpleasantness. They have no trouble remembering the strikingly colored creature and its bad taste. They are not likely to repeat such experience.

Large milkweed bugs (Oncopeltus fasciatus)
on milkweed seed pod. Adults and nymphs
© Beatriz Moisset
Milkweed beetle (Tetraopes tetrophthalmus)
© Beatriz Moisset
The monarch butterfly is not the only animal that advertises its bad taste by sporting bright colors. Other insects that feed on milkweeds, like the milkweed beetles and milkweed bugs, are also colorful, in red and black; we can be sure that they are just as bad tasting. Similar cases abound in nature, not only insects but also vertebrates. Most frogs are green or have brown spots, colors that blend well with vegetation and help them remain unnoticed. The so-called poison dart frogs are the exception. Their backs are glossy red. The name tells you that these frogs produce powerful toxins, so much so, that native peoples use them to smear the tip of their darts in order to make them more lethal.

Dendrobatid frog, Peru
© Tim Ross. Wikicommons

Polished Lady Beetle (Cycloneda munda)
Ladybeetles are another example of
brightly colored bad tasting insects
© Beatriz Moisset
So, as I said at the start, a monarch's lovely colors are due to a constant battle with their enemies. In a perfect world (perfect for monarchs, that is) these butterflies wouldn't need to be loaded with toxins, nor would they need to tell their enemies to keep away. In such a perfect world, monarchs would have plain colors. Is this what we want?

The monarch caterpillar is also toxic
and also has bright warning colors
© Beatriz Moisset

Further readings:

Sunday, September 3, 2017

Imitation is the Best Form of Protection in Some Cases

Not a bee, but a mimic, the fly Eristalis© Beatriz Moisset
A stroll among the flowers allows me to see numerous bees of different sorts, zipping along from blossom to blossom. Just as numerous are other winged insects that look very much like bees. The experienced eye recognizes them for what they are, flower flies impersonating the stinging insects. But those unfamiliar with bees or with insects, in general, may assume that these flower flies are bees. They may even recoil in fear of a sting although the flies are innocuous, lacking such powerful weapon.

A wasp mimic, Spilomyia sayi © Beatriz Moisset
Those flies who imitate bees or wasps have a reason for playing this masquerade. They are not interested in fooling us, humans. Their deception is aimed at their predators, mostly birds. However, the ruse is so effective that it even we fall for it.

Syrphid flies, also known as flower flies or hover flies, are almost as assiduous in visiting flowers as bees are. They drink nectar and sometimes also feed on pollen. Although not as efficient as bees as pollinators, they deserve some credit and occasionally their contribution to pollination is significant. Another group of flies that visit flowers with great frequency includes the so called bee flies.

Both, flower flies and bee flies mimic bees or, in some instances, wasps. The imitation is very specific in some cases. The so called drone fly, Eristalis tenax, looks like a honey bee. The name is appropriate, considering that male honey bees, drones, have large eyes, and these flies have even bigger eyes. Both, the fly and the honey bee are European. The imitator evolved along with its model in that continent. Another European flower fly that mimics honey bees effectively is the narcissus fly, Merodon equestris.

Other flower flies and also a robber fly imitate bumble bees. They have a furry coat and even buzz like bumble bees.

Bumble bee mimic, Mallota bautias © Beatriz Moisset
The smaller flies, members of the Syrphinae subfamily apparently are mimics of some or another of the many solitary bees. In most cases one cannot be sure of the model chosen for this mimicry.

A honey bee, the model for many mimics © Beatriz Moisset
It is a peculiar thing that some imitations are extremely good, while others are rather general in character. Biologists speculate that even a not-so-good imitation may serve the purpose of deceiving the enemies and this is why such types of mimicry persist in nature. It is also possible that the predators don’t see exactly what we see and the mimicry is convincing enough for them.

This is just one type of mimicry. Other insects take the appearance of their surroundings, which makes them nearly invisible. Still others look like bird poop, not an appetizing sight for a snack seeker. Stay tuned for descriptions and illustrations of more of these ingenious survival mechanisms.

References

Tuesday, February 21, 2017

Unexpected Liaisons, Mites and Bees

Mason bee with phoretic mites
Wikicommons © Orangeaurochs
We think of mites as annoying tiny parasites that cling to us and make us itch. If we see an insect covered with mites we feel sorry for it, assuming that the poor thing must be itching terribly and being weakened by the blood sucking pest. This is true in most cases, but curiously there are some exceptions. Believe it or not, some bees, wasps and beetles are perfectly happy with such companions. They bus around the little fellows from plants to nests. This earn the passengers the name of phoretic mites.

Carpenter bee (Xylocopa) with phoretic mites
Wikicommons © Gideon Pisanty
Mites and ticks are not insects. They are related to spiders, and most of them have eight legs, just like spiders. Mites are tiny; most of them are smaller than the tip of your ball point pen, so it is not surprising that we know very little about them. We would be quite surprised at the immense variety of mites and the large number of species. Many feed at the expense of animals, like the ones mentioned at the start of this piece, but many more feed on plants, fungi or bacteria.

Acarinarium of carpenter bee (Xylocopa)
Wikicommons © T. B. Fletcher (1914)

Getting back to the mites covering a bee. Little do you know that these particular kind of mites are the bee's friends to the point that the bee provides transport for them. Some bees have a small compartment or pouch on their bodies where mites can ride comfortably to the bee's nest. This organ is called an acarinarium, from the Greek word acarus (plural acari), which means mite.

It turns out that the mites feed on parasites that are prone to invade the bee's nest where she is raising a family. Thus the mite provides a valuable service to the bee which is greatly appreciated and compensated.

Some wasps have a similar mutualistic arrangement with mites and carry them to their nests. Carrion beetles transport mites to fresh carcasses. The mites feed on fly maggots, the beetle's competitors.

Potter wasp with acarinarium

Carrion beetle with phoretic mites

Monday, February 20, 2017

Spurs: Hard to Get Nectar

Violet.
© Beatriz Moisset
 Many flowers are very particular about their clientele. They have developed ways to make themselves attractive to certain flower visitors while discouraging others. They do so by adopting a certain shape. The spurs of many flowers serve this purpose. A petal or a sepal develops an elongated hollow spike. This is what botanists call a spur.

Violet (Viola mirabilis). Note the spur
Wikicommons. © Antti Bilund

Violets have a spur. Nectar is collected at its bottom. A pollinator needs a tongue long enough to reach the hidden nectar waiting in this special vessel. The rest of the flower is so designed that the insect gets covered with pollen while performing this task. If it is carrying pollen from a previous flower visit, it is likely to deposit it on the stigma. Only long tongued insects can take advantage of this flower and they need to develop an efficient way to approach this specially shaped blossom. After a few times they get better and better and proceed faster. The most common pollinators of violets are small, solitary bees.

Bumble bee visiting a jewelweed blossom
© Beatriz Moisset
Jewelweed (Impatiens) also possess a spur. The flower itself is a small chamber just a little larger than a bumble bee. The petals form a curtain that slightly blocks the entrance to this chamber. Bumble bees are pros at collecting nectar from these flowers. Their plump bodies fit inside the chamber like a finger in a glove and their long and flexible tongues are suited to the curved spur.

Columbine.
© Beatriz Moisset

Columbines have not one but five spurs. Each petal is shaped like a long hollow horn ending on a knob. This is where the nectar gathers. Long tongued insects and hummingbirds pollinate these flowers. In most species, the flower nods or points downward, and the spurs point to the sky. This arrangement seems to be agreeable to their most common pollinators, hummingbirds.

Columbine.
© Beatriz Moisset
By contrast, the flowers of the alpine columbine remain erect, don't nod. They are also creamy white, a color favored by moths. And thus, they are preferably pollinated by large moths, the so called hawkmoths. A few other species of columbines, including the Colorado blue columbine, also face upwards and are also pollinated by moths.

Columbine and carpenter bee
stealing nectar
© Beatriz Moisset
Jewelweed and ants
stealing nectar
© Beatriz Moisset
This specialization has advantages but it also has some disadvantages. Not all flower visitors behave like honest pollinators. These difficult flowers are an invitation to cheating. Some visitors learn to take a shortcut, especially if their tongues aren't long enough to reach the bottom of the spur. They approach the flower from the side. Perhaps, they can smell the sweets through the walls of the spur. A quick bite or a stab through the delicate petal may be all it takes to reach the hidden food. Carpenter bees, bumble bees and even ants have been seen performing this robbery.


List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2017