Pollen Positives

 

Giant Ragweed, the bane of many fall allergy sufferers.

While fall is welcomed for the relief it gives from the long, hot summer, it is also a season when allergies run rampant.  These allergies are caused by various pollens, and those who suffer might wonder if there are any positives to pollen at all.  The answer is yes!

The definition of pollen is a fine, powdery substance consisting of microscopic grains discharged from the male part of a plant.  It is necessary for reproduction, and is transported by the wind, insects, or other animals. The grains from each species have a distinct symmetrical shape, surface pattern, and overall structure, and are easily recognizable under a microscope.  Due to their high resistance to decay, pollens have been commonly found in both recent and ancient geologic sediments.  In fact, the study of plant pollen in both living and fossil form is known as palynology. Since pollen is produced in large quantities at certain times of the year, it is often a significant component of the Earth’s atmosphere.

Scanning Electron Microscope (SEM) image of pollen grains, showing their unique shapes. (Credit: Dartmouth College, Electron Microscope Facility)

Many flowering plants produce all-important nectar, but it is pollen that is the most highly nutritious offering, consumed by virtually all bees, as well as beetles, flies, butterflies, birds, and mammals. Most plants produce pollen in excess, to ensure that at least some of it is used for pollination.  Pollination occurs when pollen is transferred from the male anther (fertilizing organ) of a flower to the female stigma (receptive tip of the pistil) of the same flower or one nearby.  This is often accomplished with the help of the animal pollinators listed above. This time of year, the plants that produce the most pollen are Giant Ragweed (Ambrosia trifida) and Cedar Elm (Ulmus crassifolia).

Like all ragweed species, Giant Ragweed is in the genus Ambrosia, because it was long ago believed that it would grant immortality or eternal youth to those who consumed it. Giant Ragweed can grow from 6 to 20 feet tall, especially in roadsides and disturbed areas. Flowering occurs from June to October, with inflorescences forming a spike or spikes made up of many tiny flowers at the top of the plant. These flowers are wind-pollinated, releasing copious amounts of pollen in the fall, eventually developing into small burs tipped with several miniscule spines. 

Giant Ragweed flowers.

Giant Ragweed seeds (burs).

Unlike many other tree species, Cedar Elms flower from late summer to early fall, usually July through September. Their flowers are tiny, pale reddish-purple, lacking petals, and they appear in clusters at the leaf axils. They are wind-pollinated, and after pollination they develop into flat, oval, winged seeds called samaras, which are an important food source for deer, squirrels, and birds. This fall flowering and fruiting is a distinctive feature of Cedar Elms and helps to distinguish them from other native elm species.  They are called ‘cedar’ elms for their propensity to grow in the same habitat as Ashe Junipers, which are colloquially (but incorrectly) called ‘cedars.’

Cedar Elm flowers.

Cedar Elm seeds (samaras).

Pollen plays a critical role in plant reproduction, and is a nutrient-dense resource for bees and other animals.  For humans, a vast number of crops depend on pollination for their existence, including one-third of the world’s food crops such as almonds, chocolate, and coffee.  Due to their regular reproduction cycles requiring pollen, plants sustain ecosystem services such as moderating temperature by providing shade and releasing moisture into the air, producing oxygen, stabilizing soil, and creating wildlife habitat.  That’s how pollen is positive for us and for the environment!

Neither Hummingbird nor Bumblebee

 

Hummingbird or bumblebee?  Neither!

Take a closer look when you see what you think is a small hummingbird hovering about and nectaring on the tubular flowers in your garden.  It just might be a Snowberry Clearwing (Hemaris diffinis), one of our more common hummingbird moths.  

Moths in the genus Hemaris are often generically called hummingbird moths, due to their ability to fly and move just like hummingbirds. They are rather plump moths, and the tip of their abdomen opens a bit like a fan. Many are brown or black with some yellow, so they are also good bumblebee mimics. Several species have clear wings, as they lack as many wing scales as other lepidopterans, and they actually lose the ones they do have shortly after they emerge due to their highly active flight tendencies.  

This adult Snowberry Clearwing just emerged from a winter spent in leaf litter,
still with all the scales on its wings.

The Snowberry Clearwing is about 1.25 to 2 inches in length, with a yellowish thorax above, a black abdomen with a yellowish band near the tip often split in two, and the namesake clear wings. Like other hummingbird moths, they generally fly during the day, but may continue into the evening if they have found a particularly good nectar source. Their proboscis or sucking mouthpart is quite long, so they prefer to sip from tube-shaped flowers. 

An adult Snowberry Clearwing showing its yellow thorax, black abdomen with a
yellow stripe, and signature clear wings.

The adults start flying in March after emerging from the leaf litter beneath their host plant where they spend the winter as a pupa protected by loose silken cocoon.  Females attract males by broadcasting a pheromone from the glands at the tip of the abdomen, and after mating, they lay individual, tiny, round green eggs on the underside of the leaves of the host plant.  In the south, they typically produce more than one generation each summer, flying well into November.

The common name for the Snowberry Clearwing comes from the fact that it was first described in 1836 in the northeast, where it uses Common Snowberry (Symphoricarpos albus) as a host plant, a native plant in the Honeysuckle family that grows in the northern half of North America. In the southern US, the preferred native host plant for this moth is Coral Honeysuckle (Lonicera sempervirens), which can be purchased at most native plant nurseries.  It is a high-climbing, twining vine to 20 feet long, with smooth, paired semi-evergreen leaves and clusters of red, tubular flowers.  In the wild, they also use our native White Bush Honeysuckle (L. albiflora), which is more shrub-like with twining branches that have smooth, paired deciduous leaves and clusters of creamy white tubular flowers.

Coral Honeysuckle

White Bush Honeysuckle

The larva or caterpillars of the Snowberry Clearwing are commonly called hornworms, due to the horn-like projection on their posterior end.  They are up to 2 inches long, blue-green above and yellow-green along the sides, with black spots and a black horn.  Uncommonly, they can also take a brown form with the same black spots and horn.  They match the foliage of their host plants so well that they are often very difficult to find. 

Snowberry Clearwing larva, green form.

Snowberry Clearing larva, brown form.

Why Insects Matter

 

Insects are terrific pollinators!

As the growing human population transforms our planet, the global insect population is declining at an unprecedented rate of 2% a year. The world has lost 5% to 10% of all insect species just in the last 150 years, so in 40 more years we could lose one third of all insect species. In a study just published in the journal Science, a working group called the ‘Status of Butterflies in the U.S.’ found that the total abundance of butterflies in the U.S. declined by 22% from 2000 to 2020.  Said another way, one in five butterflies have vanished.

Many butterfly species, including the Monarch, are declining in abundance.

What is driving this precipitous drop in insect populations and why does it matter? Insect populations are struggling due to several factors, including deforestation/habitat loss (due to development), non-native invasive species, pesticide use, artificial light pollution, and climate change.  As a result, the populations of other animals, crops, and flowers that rely on insects to survive also struggle.

Non-native, invasive plants, like Ligustrum species, often overtake native habitats.

Scientists say that it is impossible to have an insect-free life on this planet. They perform many essential services that are vital for humans’ quality of life. Pollinators such as bees, butterflies, moths, and many other types of insects are necessary to produce diversity and abundance in our food supply, including crops such as coffee, chocolate, blueberries, apples, almonds, avocados, and pumpkins, just to name a few. In fact, pollinators help ensure that about 75% of the world’s flowering plants and 35% of the world’s food crops are produced.  Other scientists estimate that one out of every three bites of human food are directly related to the work of pollinators such as bees, butterflies, moths, beetles, and other insects.

Moths and beetles are pollinators, too!

Plant and animal waste would pile up if it weren’t for the services of dung beetles and other insect recyclers. Insects like dragonflies, ladybugs, green lacewings, ground beetles, and parasitic wasps keep what we call the ‘pest’ species at bay – the mosquitos, ticks, fleas, lice, and flies that can carry disease as well as crop pests such as armyworms, cutworms, and wireworms.  

Dung Beetles hard at work.

Roseate Skimmer dragonfly eating a mosquito.

Most humans like birds, but most are also unaware of the fact that 96% of birds would not be here without insects. It takes 6,000 to 9,000 caterpillars and other insects to feed a clutch of four to six Carolina Chickadee offspring. Multiply that by the fact that most all avian nestlings and fledglings eat some form of insects, and you very quickly realize how important they are to the food web. Insects are also the main food for all of the fish, so they are the glue that binds together every terrestrial and freshwater ecosystem on the planet.

Many bird species, like the endangered Golden-cheeked Warbler,
feed insects to their young.

What can be done to reduce this downward trend?  The good news is that the things we do in our own backyards can actually make a difference when it comes to insect conservation. First and foremost, reduce or (better yet) replace your non-native lawn with native plants.  Lawns make up about 50% of Austin’s green space, so turning them back into native plantings would provide significant benefit to insects. 

Replace your lawn with native plants -
extra bonus for providing water!

Eliminate all pesticide use, including mosquito spraying. The spray contains pyrethroids which are advertised as “safe as chrysanthemum flowers”, but they are a much stronger synthetic version that is chemically designed to be more toxic with longer breakdown times.  This increased potency compromises the human body’s ability to detoxify the pesticide in addition to killing all insects, not just mosquitos.

Mosquito spraying kills all insects,
not just mosquitos.

Light pollution contributes to insect decline.

And last, but not least, turn your exterior lights off at night so as not to affect the behavior of night-flying insects (this also benefits birds during spring and fall migration). Artificial lighting can disorient moths and confuse their sense of direction, causing one third of those that swirl around a light at night to die from exhaustion or predation. Excess light also disrupts the mating flashes of fireflies and confuses insects like mayflies by bouncing light off of asphalt and causing them to lay their eggs in the street instead of in a lake or stream.

A Parade of Pollinators

Fall-blooming plants like Goldenrod attract a variety of insect pollinators.

Much has been written lately on the importance of pollinators, as they are vital to creating and maintaining the habitats and ecosystems that many animals (and humans!) rely on for food and shelter.  In fact, more than one in three bites of food we eat or beverages we drink are directly dependent on the success of pollinators. While most people think of bees as the primary pollinators, or even charismatic groups such as butterflies and hummingbirds, pollinators also come in the form of wasps and flies.

This time of year, you can find many of these bees, wasps, and flies nectaring on and pollinating our fall-blooming plants.  Aside from the well-known but non-native European Honey Bee, other native bee species that are still around this time of year include the Metallic Epauletted-Sweat Bee (Augochloropsis metallica), American Bumblebee (Bombus pensylvanicus), Southern Carpenter Bee (Xylocopa micans), Parkinsonia Carpenter Bee (Xylocopa tabaniformis parkinsoniae), and Texas Carpenter Bee (Xylocopa virginica texana).

Metallic Epauletted-Sweat Bee

The uncommon Metallic Epauletted-Sweat Bee is a small bee, to 0.5 inches, overall metallic green with distinctive scale-like coverings at the base of each amber-colored veined wing.  It nests in soft ground, and is especially attracted to asters, grapes, and legumes.  

American Bumblebee

The American Bumblebee is common and robust, to 1 inch, with a thorax yellow in front and black in back, an abdomen with the first three segments yellow and the rest black, and mostly black veined wings. Once abundant, populations have declined significantly in recent years, and it is listed in Texas as a species of ‘greatest conservation need.’

Carpenter bees are typically separated from bumble bees by their big, shiny abdomens.  They bore into the surface of wood to build their nests, often leaving a small pile of sawdust underneath. Due to their large size and heaviness, carpenter bee species often perform what is called ‘nectar robbing’, using their mouthparts to bite through the base of tubular flowers to access nectar rather than entering the flower directly.

Southern Carpenter Bee

The uncommon Southern Carpenter Bee is large, to 1 inch, with the female being shiny blackish overall and the male more of a glossy dark greenish-blue, both with smoky veined wings.  

Parkinsonia Carpenter Bee, nectar robbing

The more common and endemic Parkinsonia Carpenter Bee is a bit smaller at 0.8 inches, overall blackish, with males having gray-blue eyes and females with dark blue eyes, both with a black abdomen with four distinct yellow bands on each side that do not meet in the middle, and smoky veined wings. 

Texas Carpenter Bee, nectar robbing

Also common is the Texas Carpenter Bee, to 1 inch, with a thorax covered in yellow hairs except for a round black spot on top, a shiny black abdomen, and smoky veined wings. 

Blue-winged Scoliid Wasp

Wasps differ from bees in that they are smooth, shiny, and often slender or narrow-waisted. The Blue-winged Scoliid Wasp (Scolia dubia) is an uncommon native wasp, to 1 inch, overall black with a mostly reddish abdomen (sometimes with a large yellow spot on each side), and dark blue veined wings. Adults provision their nests with beetle larvae, commonly of Green June Beetles. 

Fraternal Potter Wasp

The Fraternal Potter Wasp (Eumenes fraternus) is an uncommon native, to 0.8 inches, overall black with an elongated but swollen waist, a bulbous tapering abdomen, with an ivory stripe behind the head and some before the waist, two ivory side spots and a stripe near the abdomen’s tip, and dark amber-brown veined wings. Females fashion unique, marble-sized urns of mud as nests, one for each egg, and provisions them with small caterpillars.

Potter wasp nest

While many view flies as pests, flies are actually second in importance to bees as pollinating insects.  Flies pollinate more than 100 cultivated crops such as cocoa, strawberries, apples, blackberries, peaches, onions, parsley, and carrots.  A large number of wild native plant species, including many medicinal plants, are aided from fly pollination as well.  In our area, two interesting fly species are the Oblique Stripetail Fly (Allograpta obliqua) and the Four-speckled Hover Fly (Dioprosopa). Both are native but uncommon, most often seen through November on a wide variety of flowering plants with or near aphid colonies.

Oblique Stripetail Fly

The Oblique Stripetail is a small fly, to 0.3 inches, with reddish-brown compound eyes, transverse bands on a dark abdomen with four longitudinal yellow stripes near the tip, and clear veined wings. It is a member of the hover fly family, having the rare ability to hover or fly backward.  

Four-speckled Hover Fly

The Four-speckled Hover Fly is a bit larger, to 0.5 inches, with dark brown compound eyes, a black abdomen with two pairs of whitish speckles or dashes, and a pair of clear veined wings with a brown leading edge.  Its larvae eat aphids, and this fly is considered to be a wasp mimic, due to its thin, ‘wasp-waisted’ abdomen.

The species shown above are only some of the many distinctive species of bees, wasps, and flies that are important pollinators. This fall, take a closer look at the insects that are busy nectaring on your plants, and pollinating them in the process. Make a difference to their populations by adding a wide variety of native plant species in your yard that bloom from spring to fall, and be sure that you avoid using pesticides.  Your actions alone can help promote a healthy parade of pollinators for many months of the year, that in the end benefit us all!