Bug Stories

An adult Large Milkweed Bug (Onopeltus fasiciatus) on
Tropical Milkweed (Asclepias curassavica) 

Two brightly colored species of bugs are conspicuous in the fall and they are not even trying to hide.  They are the Large Milkweed Bug (Oncopeltus fasiciatus) and the Boxelder Bug (Boisea trivittata).  These two are true bugs in the Order Hemiptera, a group that also contains aphids, leafhoppers and stinkbugs. Hemiptera go through incomplete metamorphosis.  When a true bug hatches, it enters a larval stage called a nymph.  Nymphs look like miniature adults but lack wings.  The nymphs eat and grow.  As they grow, the nymphs molt their exoskeletons several times. With each molt they becomes larger nymphs. After going through several nymphal stages, they undergo a final molt to make the winged adult.  This type of development contrasts with complete metamorphosis where a worm-like larva emerges from the egg.  After several molts, the larva makes a cocoon or chrysalis where a complete rearrangement of the body plan produces the adult.  Moths and butterflies are typical insects with complete metamorphosis.  The larvae are the caterpillars and the adults are flyers.     

Large Milkweed Bugs spend much of their life on milkweeds (Asclepias sp).  Like Monarch Butterfly larvae, Large Milkweed Bugs consume their host milkweed and incorporate cardiac glycoside toxins into their bodies. Like Monarch Butterflies, Large Milkweed Bugs have a bold pattern of orange and black to warn predators.  

Large Milkweed Bugs on a fruit of Asclepias sp.

Large Milkweed Bugs have four nymph stages and at each stage, the nymphs are bright orange.  The adults have wings that are black with an orange “X” pattern.  Both nymph and adult Large Milkweed Bugs use a mouthpart called the proboscis to suck nutrients from their host milkweed plant.  Adult Large Milkweed Bugs survive the winter in this area by burrowing in leaf litter and entering a hibernation-like state called diapause. 

Large Milkweed Bugs mating on a Milkweed

Eggs of Large Milkweed Bugs on the underside
of a Tropical Milkweed leaf. 

A mixed group of adult and nymph Large Milkweed Bugs on the leaf of
Common Milkweed (Asclepias syriaca). The large nymphs have small, black,
non-functional wings.  

Large Milkweed Bugs nymphs feeding on seeds of Common Milkweed. 

It is no surprise that Boxelder Bugs live on Boxelder trees (Acer negundo).  Boxelders are not elders at all, they are maples.  Boxelders are interesting for a couple of reasons.  First, they are the only North American maple with compound leaves.  Boxelder leaves typically have 3-7 leaflets.  Second, Boxelder is the only North American maple with separate male and female trees.

A single compound leaf with three leaflets
of Boxelder (Acer negundo).

Winged fruits with seeds of Boxelder.

Boxelder Bugs have a wider range of hosts than the milkweed bugs, laying their eggs on Boxelder, other species of maple and ash trees.  The eggs hatch and bright orange nymphs emerge.  The nymphs feed on their host plant, particularly the seeds, grow and molt.  Like the Large Milkweed Bug, Boxelder Bugs have four nymphal stages and then molt into the winged adult. 

Boxelder Bug nymphs (Boisea trivittata) on the bark of
a Boxelder tree (Acer negundo).  The large nymphs have
non-functional wings. 

A group of Boxelder Bugs with both adults and nymphs. Adult
Boxelder Bugs have dark brown wings with orange stripes.

Adult and nymph Boxelder Bugs.

The adult Boxelder Bugs are dark brown to black with deep orange stripes on the wings.  The colors are warning signals to predators not to eat these bugs.  Indeed, Boxelder Bugs are protected by chemical defenses.  Unlike Large Milkweed Bugs and Monarch Butterflies, Boxelder Bugs do not ingest toxic chemicals from their host plants but make them from scratch.  Boxelder Bugs have glands in their abdomen that release noxious smelling (and tasting) compounds if attacked by a predator.  Because the nymphs feed on the Boxelder seeds large groups of Boxelder Bugs of different developmental stages are found on the female Boxelder trees during the fall.     

Boxelder Bug nymph feeding on a Boxelder seed.

Be on the lookout for these bright bugs as the bug season winds down.

Advice from a Caterpillar

While Alice was adventuring in Wonderland, she met a hookah-smoking caterpillar who asked her unpleasant questions and gave her advice.  The caterpillars we run into can give us advice too. 

Monarch Butterflies (Danaus plexipus) feeding on Aster sp. in the
North Carolina mountains

Two common butterflies in the Southeastern United States advise their predators, and us, how dangerous they are.  Monarch Butterflies (Danaus plexipus) are the most charismatic of our butterflies.  They are large, brightly colored and undertake epic migrations from Mexico to Canada and back.  If you plant milkweed in your garden you will probably have Monarchs.  They lay their eggs on the milkweed (Asclepius sp.) leaves.  

Butterfly Weed (Asclepius tuberosa), a species of
Milkweed

The eggs hatch into caterpillars with alternating white, yellow and black stripes.  Monarch caterpillars are not trying to hide.  That is because the milkweed upon which they feed is laced with cardiac glycosides, a potent toxin.  

A caterpillar of the Monarch Butterfly
on Tropical Milkweed (Asclepius curassavica)

Cardiac glycosides, as the name suggests, interferes with heart function that can result in heart failure. Cardiac glycosides also interfere with the digestive tract and muscular system of mammals that ingest them.  Not only that, these molecules taste bad.  The target of cardiac glycoside is a protein pump found in the membranes of all animal cells called the sodium-potassium ATPase.  This large protein maintains the proper balance of sodium and potassium ions in cells.  This is particularly important in muscle and nerve cells.  Monarch caterpillars take in the toxin when they eat milkweed leaves and store it in their bodies.  This makes them less palatable to predators like birds or mice.  The adult Monarchs retain cardiac glycosides after metamorphosis and this protects them from their bird predators.  A good question is; Why don’t the cardiac glycosides kill the monarchs?  It turns out the Monarchs carry a mutated version of the gene for the sodium-potassium ATPase that imparts  resistance to the effects of cardiac glycoside.  So the caterpillars can eat toxic milkweed with impunity, retain the toxin, advertise their toxicity with bright colors and patterns and pass this protection on to the adults. 

A Gulf Fritillary butterfly feeding on Lantana camara.

Another caterpillar giving advice is that of the Gulf Fritillary (Agralus vanilla).  The Gulf Fritillary butterfly, like the Monarch is large with a distinctive pattern of vivid colors.  When seen from above the Gulf Fritillary butterfly is bright orange with bold black spots.  The underside of the butterfly wings are brown and orange with large white spots.  

A Gulf Fritillary seen from below showing large white
spots on an orange and brown background.

Gulf Fritillaries lay their eggs on leaves of Passionflower vines.  The caterpillars hatch and eat the Passionflower leaves. Passionfllowers have chemical defense molecules called cyanogenic glycosides that protect the plant by releasing cyanide.  When a herbivore eats a Passionflower leaf they are poisoned by the cyanogenic glycosides.  But even cyanide cannot deter Gulf Fritillary larvae from eating the leaves.  The caterpillars are bright orange with black spines as if they are daring a bird to eat them.  Like the Monarch, its caterpillar is conspicuous and downright threatening.

Yellow Passionflower (Passiflora lutea) a host plant for
Gulf Fritillaries

Gulf Fritillary caterpillar on Passaflora sp.

Both the caterpillar and butterfly are protected by toxins from the Passionflower.  The adult butterfly also releases noxious chemicals from a gland in the abdomen to further deter predators.    

As a rule, boldly colored insects are toxic and should not be eaten.  I knew a young man that wanted to taste everything he could in the woods.  One day he found a Lady Bug and popped it in his mouth.  He immediately spit it out and spent the next half hour trying to get the horrible taste from his mouth.  The Lady Bug, with its red color and black spots was giving advice.  So are some of the caterpillars. 

An Asian Lady Beetle (Harmonia axyridis) aka Lady Bug
warning us not to eat it.

Basal Angiosperms II

 I wrote earlier this year about a group of plants called basal angiosperms.  These are flowering plants that branched off the evolutionary line that led to the eudicots and monocots.  Basal angiosperms have some characteristics of both monocots, like flower parts in multiples of three, and eudicots, with net veined leaves. 

Waterlilies are basal angiosperms classified in the family Nyphaeacea and grow on all continents except Antarctica.  These familiar plants grow in lakes, ponds and slow-moving streams.  They have floating leaves and brightly colored flowers that emerge from the water.  The largest waterlily in the world is from South America.  This waterlily, Victoria amazonica, has leaves that are ten feet in diameter and can support the weight of a person.  A famous nineteenth century lithograph shows young Annie Paxton standing on a leaf of V. amazonica at the English estate Chatsworth.  Annie’s father, Joseph Paxton, was the head gardener at Chatsworth and the first to get V. amazonica to flower in England.  Paxton noted the ribbed supports on the underside of the leaves of V. amazonica and used these as inspiration to design a large greenhouse at Chatsworth.  Later Paxton became the lead architect of the Crystal Palace that housed the Great Exhibition of London in 1851. 

Annie Paxton standing on a Victoria amazonica leaf at the
English estate of Chatsworth in 1849.
https://en.wikipedia.org/wiki/Victoria_amazonica
 

We could not visit the Amazon Basin to see these lilies but Fairchild Tropical Botanic Garden in Miami, Florida has Victoria sp. growing in a pond.  The Miami Victorias are not as large as those growing in the Amazon but the Florida plants sport 2-3 foot leaves that have the characteristic upturned edges.

Victoria sp leaves at Fairchild Tropical Botanic Garden
Miami, Fl

Two common waterlilies in the Southeast are the alliterative Nymphaea and Nuphar.  One is Nymphaea odorata or the fragrant waterlily.  The scientific name of the fragrant waterlily is a wealth of information.  The genus Nymphaea gets its name from the nymphs of Greek mythology.  These minor female deities were associated with natural sites, particularly water.  The species name, odorata, tells that the flowers are fragrant and help attract its beetle pollinators. Fragrant waterlily leaves are large, bright green and oval shaped with deep cleft that runs to near the center of the leaf.  The flowers are white with dozens of petals and numerous stamens. 

Fragrant Waterlily (Nymphaea odorata) in Salisbury, NC

Nuphar advena, the yellow pond lily or spatterdock, has floating leaves and a yellow flower that emerges above the surface of the water.  The petals of the flower are inconspicuous while the sepals give the flower its yellow color.  Spatterdock is widely used in traditional medicine to treat diarrhea and skin disorders. 

Spatterdock (Nuphar advena) in Palm Beach County, FL 

 Magnolias are a large group of highly successful basal angiosperms.  The family Magnoliaceae contains more than 200 species and they are found in North, Central and South America as well as East Asia. Two important members of this family in the Southeastern United States are Tulip Poplars and Southern Magnolias. 

Liriodendron tulipifera goes by a number of names Tulip Poplar, Tulip Tree or Yellow Poplar and is among the tallest eastern trees.   Tulip Poplars in the Joyce Kilmer Memorial Forest in western North Carolina tower to heights of more than 160 feet with circumferences of greater than 20 feet.  Tulip Poplars are fast growing, long lived trees that are valuable for timber.  Tulip poplar leaves are large with four lobes and its yellow-green flowers are tulip-shaped.  The flowers have 3 sepals, 6 petals with orange at their bases and multiple stamens and carpels. 

Tulip Poplar (Lirodendron
tulipfera) flowering in April, Salisbury, NC
The flowers are shaped like tulips.

Close up of Tulip Poplar flowers showing six petals, numerous stamens and carpels.

Southern Magnolia, Magnolia grandiflora, is a forest tree with large shiny green leaves and in late spring produces large, white, fragrant flowers.  One of the primitive characteristics of magnolias is their stamens and carpels are arranged in a spiral pattern rather than a whorl.  As the petals fall from the flower the spiral-pattern of stamen scars are apparent.   The carpels that produce the seeds are in a cone that also has a spiral pattern. 

Bud of Southern Magnolia (Magnolia
grandiflora) in Salisbury, NC

Flower of Southern Magnolia with multiple petals. 

Mature flower of Southern Magnolia.  It has multiple petals, many stamens
some of which have fallen on one of the petals and numerous carpels, 

Details of a Southern Magnolia flower.  Petals are inserted at the bottom of the flower.
Next come the yellow stamens and at the top are the many carpels that will produce seeds. 

A dying Southern Magnolia flower.  In the center is the carpel that will develop into
the seed bearing cone.  The purple column below the carpels has the spirally arranged
purple scars where the stamens were attached. 

An immature cone of Southern Magnolia
with its carpels and a few stamens
still attached.

Southern Magnolia cone.  Below the cone are
scars from the stamens and below them
are the spiral scars of the petals.

A nearly ripe cone of Southern Magnolia.  Seeds are developing
inside the cone.

A mature cone of Southern Magnolia.  The bright red seeds
are being released. 

By early fall, the cones split and show bright red seeds.  The seeds remain attached for a time attached to the cone by strong, silky threads that smell, oddly enough, like Juicy Fruit gum.  

Mature cone of Southern Magnolia with red seeds.

Southern Magnolia seeds are attached to the cone by threads
that smell like Juicy Fruit gum. 

These basal angiosperms are relics of deep time.  They remind us of a world long past.  So next time you see a magnolia or a water lily or a pawpaw, think dinosaurs. 

What Good is a Ragweed?

Ragweed is notorious for causing seasonal allergies. In late summer and early fall an estimated 23 million Americans suffer runny noses, itchy eyes and respiratory congestion caused by pollen of ragweed.  This seasonal allergy, also called hay fever, is caused by an inappropriate immune response.  Our immune system identifies and eliminates foreign material like an infectious bacterium or an invading virus.  In some cases, the immune system mounts a strong attack on a non-pathogenic agent like ragweed pollen.  This overly vigorous response includes the release of a powerful molecule called histamine that causes many of the hay fever symptoms mentioned above.  Treatments for seasonal allergy usually contain an anti-histamine to counter the effects of histamine.  

Giant Ragweed Ambrosia trifida 

But ragweed has a life of its own, beyond being the cause of seasonal allergy, and an interesting life it is.   Two species of ragweed are common in North Carolina, Common Ragweed (Ambrosia artemisiifolia) and Giant Ragweed (Ambrosia trifida).  These two ragweed species are in the same family as sunflowers, the Asteraceae.  The name of the genus of ragweed, Ambrosia, is from the Greek and means food of the gods.  Ragweed seeds are highly nutritious, containing high concentrations of protein and oil.  Native Americans grew ragweed as a food crop then abandoned its cultivation when they adopted corn based agriculture.  The specific name of Common Ragweed, artemisiifolia, suggests the leaves of this plant resembles the highly dissected leaves of Artemisia, wormwood or sagebrush.   The specific name of Giant Ragweed is trifida and that refers to the three-lobed leaves of the plant. 

Common Ragweed grows to a height of about 2 feet.  It has dissected leaves and produces small, green flowers.  The flowers, which do not look like sunflowers despite being in that family, are borne on vertical, candelabra-like inflorescences.  Each inflorescence has dozens of male flowers that bear pollen-producing stamens.  Near the base of the inflorescence are a few female flowers that have the egg-producing carpel.  The flowers of ragweed are small, inconspicuous and colored green.  Plants that have brightly colored flowers use them to attract pollinators like insects or birds.  Ragweed does not depend on animal pollinators but uses wind to spread its pollen. Wind pollinated plants tend to have dull flowers.  Each ragweed plant produces about a billion tiny pollen grains in a season.  This pollen floats on the wind and a few grains pollinate female flowers.  This strategy of producing lots of pollen and casting it to the winds contributes to ragweed’s importance as an allergy health hazard because some of that pollen is inhaled by sensitive people.  Imagine billions of plants each producing a billion pollen grains and you can see the impact of this plant on human health. Each ragweed plant has a few female flowers at the base of each inflorescence where they receive the free-floating pollen.  Pollen lands on stigmas extending from the female flower and a pollen tube grows down into the flower to fertilize the egg within.  Each flower makes a single, dark brown seed that is a favored food of wildlife including quail.  

The dissected leaves of Common
Ragweed, Ambrosia artemisiifolia

Male, pollen producing flowers
of Common Ragweed

Female flowers of Common Ragweed
with their extended stigmas to collect pollen

Giant Ragweed is much taller than Common Ragweed with plants reaching 13 feet in height.  The stems bear the large, three-part leaves that give the plant its scientific name.  At the tops of stems are the inflorescences that are similar to those of Common Ragweed.  The green flowers, both male and female, carry out the same type of reproduction as the Common Ragweed with massive amounts of pollen released and brown seeds produced. 

The three-part leaf of Giant Ragweed, Ambrosia trifida

Male flowers of Giant Ragweed with yellow,
pollen bearing stamens visible.  

Female flowers of Giant Ragweed with their
stigmas extended.

 Brown fruits developing from the female flowers of Giant Ragweed.

Ragweed plants produce large amounts of pollen because wind pollination is inefficient.  Other wind-pollinated plants, like Bermuda Grass and Oaks, also produce vast numbers of pollen grains and contribute hay fever suffering.  Ragweed pollen has a molecule on its surface that makes it a potent allergen that stimulates the human immune system.  The molecule is a protein, an enzyme called pectinase.  This enzyme breaks down pectin, a complex carbohydrate called pectin found in plant cell walls.   Pectinase helps the pollen deliver the sperm nucleus to the egg, allowing fertilization and more ragweed for next year.  Remember, ragweed is not trying to make us miserable, it is not trying to give us runny noses, it is not trying to clog our sinuses.  But, in the fall of the year these things do happen because of the reproductive strategy followed by Ambrosia artemisiifolia and Ambrosia trifida. 

Back to the question, what good is a ragweed?  People often ask this question of living things they view as problems.  What good is a mosquito?  What good is a tick?  What good is a ragweed?  All these organisms had an evolutionary history before people appeared on the scene.  They lived, reproduced and adapted.  The two ragweed species in this area are highly successful.  Ambrosia artemisiifolia and Ambrosia trifida fix carbon, provide food for a variety of animals, were once crop plants and because of the shape of a protein on the surface of their pollen, cause allergies.   None of these traits was the result of design for a human, utilitarian end. With the gene editing technology CRISPR it is now theoretically possible to deliberately cause the extinction of a whole species.  This very thing, intentional extinction, has been discussed to rid the world of a species of a mosquito that transmits one type of malaria.  I hope humanity has better sense than to eliminate even more species than we have already done, be it the vector for a terrible disease or the cause of hay fever.  

Fairy Rings

A perfect circle of mushrooms.  They pop up after a rain in summer or fall.  A fairy ring.  The name suggests magic and there is a deal of biological magic taking place.  There are several fairy rings in our suburban neighborhood in North Carolina.  The one we see the most is a ring of the poisonous mushroom Chlorophyllum molybdites. This fairy ring starts with a single, microscopic spore of the fungus landing in the soil.  This spore germinates and sends out hyphae, microscopic threads of cells, that absorb nutrients from the soil.  The hyphae grow out symmetrically in all directions making a circular colony fungus. As the colony gets larger the older part in the center dies and the living portion is along the perimeter of the colony.  When the moisture and temperature conditions are right, the hyphae on the circumference send up mushrooms in a ring.  The mushrooms carry out sexual reproduction and release more spores.  These spores float through the air and if they land on a favorable patch of ground, a new fungal colony can form.    

A fairy ring of Chlorophyllum molybdites on a lawn in Salisbury, NC. 

Chlorophyllum molybdites makes a large white mushroom.  The stalk of the mushroom has a distinctive ring just below the cap.  The mushroom’s cap has off-white scales on the top and spore producing gills on the bottom.  One of the unique features of Chlorophyllum molybdites is it makes green spores.  The spores give the gills a pale green color too.  Spore prints are a good way to see the color of fungal spores.  To make a spore print you remove the stalk from the mushroom, lay it on a piece of paper, cover it with a bowl and wait 24 hours.  The spores are released and fall straight down onto the paper making an exact print of the gills and showing the color of the spores too. 

A single mushroom of Chlorophyllum molybdites just emerged from a lawn.

Two Chlorophyllum molybdites mushrooms with scales on the cap. 

The underside of the cap of Chlorophyllum molybdites showing the ring on the stalk,

A closeup of the gills of Chlorophyllum molybdites with the green color.

Spore print of Chlorophyllum molybdites.  The spores make an exact impression
of the gills and show the spore color.

Chlorophyllum molybdites has several common names.  The most interesting is vomiter from the consequence of ingesting this poisonous mushroom.  Chlorophyllum molybdites causes most of the mushroom poisoning cases in the United States.  A person unlucky enough to eat Chlorophyllum molybdites experiences gastrointestinal distress.  It starts with cramps, then vomiting and diarrhea, sometimes-bloody diarrhea.   Chlorophyllum poisoning is almost never fatal and the symptoms clear up in a couple of uncomfortable days. 

Fairy ring season is upon us.  Enjoy the magic but don’t eat the mushrooms.