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.


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

© 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.

© 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.

© 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

Sunday, February 12, 2017

Butterfly Pollination

Fritillary butterfly on butterfly weed
© Beatriz Moisset
When you mention pollinators to people, the immediate answer is: bees and butterflies. Bees, yes, the 20,000 species or so do a huge percentage of pollination. Some plants depend entirely on bees for this function. However, when it comes to butterflies, a different story emerges. Other insects, such as flies, wasps and moths are known to do a respectable amount of pollination, probably far more than butterflies do. Some of the mentioned insects are indispensable to certain plants, such as figs, cacao and yucca. Some flies are used in farming.

A great variety of pollinators and flower visitors
© Beatriz Moisset
Butterflies visit flowers but that alone doesn't make them good pollinators. They are easily noticed because of their large size and color. That is why the general public takes notice, but biologists have not paid a lot of attention to the role of butterflies as pollinators. So it would be nice to know a little more about them and how much credit they deserve.

Bumble bee on Helenium
© Beatriz Moisset

Let us compare a bumble bee with a butterfly in a field full of ragworts, for instance. Ragworts are pretty, daisy-like, rather weedy yellow flowers. A bumble bee hastily gathers pollen and nectar and moves on quickly from blossom to blossom in one plant, next it moves on to the next plant and the next, without wasting any time. It finally rushes home to feed a hungry brood with the gathered supplies. A butterfly, on the other hand, is free from family obligations. It only needs some nectar to quench its thirst so it lazily sits on a flower, unfolds its long tongue and drinks at leisure. It takes off and wanders away apparently aimlessly. Farther down it may finally land on another flower and drink some more nectar. Later on it may visit another plant a good distance from the previous ones and so on.

It is obvious that the bumble bee performs more pollination because of its diligent behavior. However, the butterfly is doing something important by transporting pollen to plants that are a good distance from each other. It is performing cross pollination and ensuring a good mixing of genes. Plants benefit from this increase in genetic diversity. Furthermore, recently researchers have learned that the pollen, stuck to a butterfly's long tongue, stays fresh for a good time and ensures this valuable pollination at a distance.

Red banded hair streak butterfly on Helenium
© Beatriz Moisset
Butterflies seem to do more pollination in tropical regions than in temperate ones. Butterflies and hummingbirds are good at finding nectar inside long-necked or trumpet shaped flowers. They are attracted by red flowers, which are rather common in the tropics. Bees are color blind to the red color and prefer yellow and blue or purple ones. Butterflies, like hummingbirds, have a good vision for the red color.

A number of flowers are completely dependent on butterflies for pollination. Some South African orchids fall in this category. Another flower dependent on a butterfly for pollination is a member of the pea family, the Peacock Flower that grows in the Caribbean.

Orange sulphur butterfly on asters
Notice the long tongue
© Beatriz Moisset

In summary, butterflies, while not the most efficient pollinators, are important, even essential, in some instances.

Also see:
Pollinator Foraging Behavior and Gene Dispersal in Senecio (Compositae) (contribute to cross pollination, farther distances than bumble bees)