Month: November 2024

I am writing this post on Thanksgiving Day, and I can hear football in another part of the house while I sit here with cat in lap. Here in Georgia, we are still officially in the growing season, although that will end in the next few days since a cold front has pushed through today, ushering in much colder conditions that will result in temperatures in the mid-20s next week. It will be a while before we see snow, though, and in fact we only get it every couple of years in Georgia, so we may not get any snow at all this La Nina year, since La Nina winters are usually warmer and drier than usual in the Southeast. Many of my friends from more northern areas have already experienced killing freezes and even snow so today I want to talk about how snow on the ground affects your gardens.

What does the phrase “blanket of snow” mean?

When you hear the term “blanket of snow”, what does it mean to you? To me it means enough snow to completely cover the ground. Quora says it is a metaphor: “Everything is or was covered with snow thick enough to hide the actual objects and their shapes like a blanket would hide the objects it was covering.” Certainly, a thick enough covering of snow will mask the shapes of objects underneath it, just like the blanket on my bed hides the outlines of my legs. But I also think of a blanket as an insulator that keeps heat trapped underneath it and a blanket of snow can also do that for the ground beneath it. Snow also has weight, an early snowfall landing on autumn leaves can quickly strip a tree of its leaf cover if the snow is heavy enough to release the leaves from their branches. Linda has discussed damage to garden trees and shrubs from snow in a previous post.

When does snow form and fall?

Snow can come from several weather sources. In a previous blog post I discussed lake effect snow, and this week is likely to have some very big lake effect snows downwind of the Great Lakes (up to 5 feet!) because of the combination of very cold air with the record-setting high temperatures the Great Lakes are experiencing this year. Snow can also be caused by upward motion of moist air over elevated land, which becomes snow when it rises above the freezing level and drops precipitation on the mountains. For most people, snow comes when a large area of low pressure brings cold air into contact with warmer moist air at the surface. The dense cold air causes the lighter warmer air to rise over it. The air temperature drops as it goes up leading to bands of snow where the cold air and the moisture meet. If the cold air lags behind the surface low pressure, then it is unlikely to cool off the moist air enough to get snow and you may get a cold rain instead. This is the most likely way most of us will get snow if we don’t live near a large lake or mountain range.

How does snow insulate the ground?

Snow insulates the ground from the cold air above the snow by trapping air within the snow cover. This is not unlike how a down comforter works. The snowflakes fall against each other in random orientations that leave a lot of air between the individual flakes. The trapped air serves as a barrier between the really frigid air that is over the surface of the snow and the soil beneath it. In some cases, the snow is so effective at insulating the soil that the soil temperatures can be above freezing while the air above the snow cover is much colder. This is especially true when the skies overhead are clear because the top of the snow radiates thermal energy up to space very effectively when there is no cloud cover. If the soil stays above freezing, then pests and weeds will continue to live in that soil until a longer freezing spell comes along later in the winter when the ground is less protected by the snow. However, the insulation can protect from the desiccating effects of very cold, dry air on the plants that are waiting under the surface for spring temperatures to bring them back to life. A winter drought in the wheat fields of the Great Plains can lead to severe damage to the winter wheat crop since the lack of insulating snow cover leads to soil temperatures too low to sustain the wheat plants into the next growing season.

The amount of insulation snow cover provides depends on the density of the water in the snow cover. You can think of this as the ratio of snow depth to snow water equivalent, the depth of water that the snow would have if you melted it and measured the water volume that was left. Typically, the ratio of snow depth to water equivalent is roughly a 10 to 1 ratio—in other words, 10 inches of snow is equal to 1 inch of liquid water. But that varies widely depending on the temperature and weather conditions at which the snow occurred. A heavy lake effect snow near 32 F can be a ratio more like 6 to 1 while a really cold Arctic or high-altitude snow can be more like 15 or even 30 to one, resulting in a very fluffy snow that is dry and powdery with the snow crystals barely sticking to each other.

Different shapes of snowflakes affect snow cover density

The difference in the ratio of snow depth to water equivalent is due in part to the different shapes that snow crystals form depending on what the temperature and relative humidity are where they are forming in the atmosphere. The snowflakes that grow in the highest humidity levels and form near freezing are called dendrites. These are the typical snowflakes depicted on Christmas cards and in children’s books, with six-armed patterns that can be very ornate and beautiful. The dendrites usually cause the fluffiest snow covers because the edges of the flakes are rough and catch against each other, resulting in a lot of space between the flakes. Other shapes of snowflakes are denser and are also smoother, resulting in a closer packing of snow crystals that lead to a tighter snow cover. The longer the snow cover sits on the ground, the more dense it becomes as the rough edges of the snowflakes melt and smooth out, resulting in a tighter packing of the snow cover that becomes heavier and harder to shovel.

For gardeners, a blanket of snow can be not only a thing of beauty but a way of protecting your garden plants from the most extreme cold air. It can also be a way of providing moisture that will be needed by the growing plants in spring once the next growing season begins. So if you get snow, enjoy it as it covers your winter garden but also walk and drive safely if you have to go out in it. If you live in an area that does not get snow, enjoy the pictures that others post on social media and think about how a blanket of sparkling ice crystals might look in your garden.

Coming up in December: end of year summary

I plan to post a summary of the 2024 season in my December blog post. There is a lot to talk about this year, not just in the Southeast, and I hope to cover a good bit of it in that article. In the meantime, happy Thanksgiving to those of you in the United States and a happy Christmas and holiday season to all who celebrate it.

Ants are a very familiar and recognizable group of insects in our homes and gardens. Due to their common presence on or around our plants and garden pests, some people consider that they may be the cause of some of the issues that we see. For the most part, ants play important and diverse roles in their ecosystems and are usually beneficial to us in our garden settings. As with every situation, however, there are always exceptions.

Ants are in the family Formicidae, within the order Hymenoptera (making them relatives to bees and wasps). They are also eusocial, meaning that they share characteristic traits including a queen (though some species have multiple queens that peacefully share a nest) taking care of brood cooperatively (usually through workers), and reproductive division of labor (meaning that certain groups within a species play a role in reproduction while others do not). Eusocial insects are able to collect a large array of resources, store/share them within their colonies, and can have interesting and complex methods of communication through pheromones. Other eusocial insect groups include bees, wasps, and termites- though there are more eusocial ant species than all of these other groups combined with an estimated 12-20,000 species (and likely even more that are undescribed).

Ants also have very interesting and elaborate communication, movement, and mating behaviors. They send individuals to scout out ideal sources of food and nesting areas, and then use trail pheromones to navigate their way to these locations. When the mating season arrives, winged male and virgin female ants take nuptial flights and then go on to start new colonies. These newly mated queens store the sperm from these nuptial flights and will use these stores to selectively fertilize her eggs for the duration of her life.

Ants are omnivores, and feed on a variety of organic materials including fungi, nectar, seeds, plants, arthropods and other small animals (acting as predators or scavengers). Even though they do sometimes feed on plants, they rarely do enough physical damage to be very noticeable in most situations. With the exception being species of leafcutter ants (primarily found in tropical climates such as central and South America). These ants form complex societies and even farm their food. Like their name suggests, they cut leaves off plants and take them back to their large underground nests in which they cultivate and feed on the fungus that grows on these chewed leaves. They can take a significant amount of vegetation to accomplish this task, though plants often easily recover by producing new leafy vegetation. In temperate climates, we don’t need to worry about these ant species ruining our favorite ornamental tree or shrub.

There are also several ant species found in lots of different climates, which can be nuisance pests due to their nesting habits, behaviors and/or close proximity to humans – but I will not be discussing these ants in this post. The goal of this blog post is to discuss examples of common ants that can be found in our yards and gardens and what they might be up to. The Ants in our Plants, so to speak.  

Ants as Beneficial Garden Guests

Many ants are great generalist predators, especially when they work together! In fact, one of my first memorable entomological observations was a large white grub (the larva of a Scarab beetle) in my family’s lawn in Pakistan being swarmed by 40-50 ants that were working together to take down this sizeable opponent. I was 7 years old at the time, but I recall being endlessly fascinated by what I saw, and continued to observe the epic battle for nearly an hour.

If a large grub (or even slightly larger animals) didn’t stand much of a chance against a determined colony of ants, smaller soft-bodied arthropods would likely be no match! In fact, ants have been recognized as great biological control agents in agriculture, especially in tropical climates. That being said, they can also have a few behaviors that can make them detrimental to our agricultural (and garden) productivity, as I will explain in the next section.

Ants as companions to other insects

In some situations ants can act in a way that is contrary to our gardening goals by supporting, protecting, and partnering with other common pest insects. These are often referred to as ‘symbiotic relationships’ (where these organisms have a close association with one another, that may benefit one or both of these groups). You may be familiar with some of these associations, which often involve a honeydew producing insect (such as an aphid or a scale insect) being closely guarded and “farmed” by a group of ants.

The reason that several ant species associate with these honeydew producing insects is due to the fact that their waste (a sugary substance that is excreted from a diet rich in plant sugars referred to as honeydew) is an excellent nutrient rich food source. These ants will often “milk” these sap-sucking insects by manipulating their abdomens with their antennae in order to coax out more honeydew. Having such a great source of food in such close proximity also gives the ants an incentive to protect it – which means that these honeydew producing insects basically have ant bodyguards that can defend them from natural enemies (such as generalist predators and parasitoids). In some cases, ants will herd or move these sap-sucking insects to juicier plant tissues, and to safer locations. When these ants move to a new nesting site, they will bring aphid eggs with them in order to establish a new “herd”.

Seeing this in action can be quite a sight to behold. In fact, if you are seeing ants grouping around some of your garden plants in larger quantities, take a look to see if you can spot some of these honeydew producing pests as well.

This symbiotic relationship between ants and honeydew producing pests can also have significant economic and ecosystem impacts! As a meta-analysis by Anjos et al. (2022) demonstrated that although ants in various cropping systems can reduce the abundance of non-honeydew producing pests, their impact on honeydew-producing pests is reversed! This analysis showed a variety of instances in which ants decreased the number of natural enemies, and increase the abundance of these honeydew-producing pests (Anjos et al., 2022).

Ants in turfgrass

Since many ant species nest in complex underground colonies, they can move large portions of soil in order to create these dynamic living spaces. Ant nest mounds in locations where we don’t want to see them can often be a nuisance to us, and sometimes even detrimental to our plants. I receive calls about this in a turfgrass setting (especially if the turf isn’t very dense or competitive), where your plants are mowed low enough to make even smaller nests noticeable. Even though these ants feed on a variety of common turf pests like white grubs and cutworms, their nests can sometimes be unsightly. Although this usually isn’t a problem in home gardens (and raking small mounds, using a hose, and increasing your mowing height can be simple fixes which could cause the ants to relocate), in situations like golf courses where low mowing heights are an important component of play mechanics, this can be more of a problem.

As you would expect, larger ant nests that happen to be built in your home gardens can be an even larger problem, because piling large quantities of soil over turfgrass is not great for the health of the turf. Some of the ants that produce larger nests include Allegheny Mound Ants (found in the Atlantic Coast of the U.S.) which can build some large and very conspicuous nests that can be over a foot tall and multiple feet wide. Additionally, since ants like to locate their nest entrances in sunny locations, they can damage vegetation in close proximity that may be shading the nest entrance. They accomplish this by biting the plants and depositing formic acid into them and, when persistent enough, can even take down larger vegetation (such as trees) through a painstaking process of hundreds of these formic acid deposits (although this isn’t very common since they prefer to nest in more open spaces).

Ants on Peonies

If you grow peonies, you may have been waiting for this section of the Ants in Our Plants blog post, as you’ve likely seen ants on or around your peonies, especially around the flowers. This is another commonly observed mutualism that exists between some flowering plants and ants (where the flowers lure ants as a source of protection from other pests), the origins of which can be traced back to the Cretaceous Period. Peonies have extrafloral nectaries located on the base of their flower buds. These produce a honeydew-like material which is a rich source of sugars, lipids, and amino acids utilized by ants as a source of food. As ants track their way to these sugary food sources, they also protect the peonies from other flower-feeding insects such as thrips. These ants don’t harm your peonies at all so there is no need to worry about them: just marvel at this cool association between two different organisms next time you are enjoying your prized peonies.

Ants in Trees

Sometimes we can find ants in old tree cavities, and around logs and stumps. Although there are a variety of ant species that nest in these habitats, the group of ants most commonly seen in proximity to our home gardens are usually carpenter ants (Camponotus species). These ants primarily chew through dead wood, and create nesting sites in imperfections and cavities of older, often damaged and deteriorating hardwood trees. They excavate smooth nests within these cavities, and you can sometimes see a characteristic pile of sawdust around the entrance. In some situations these ants can be a structural pest in homes, especially if you have water damaged wooden structures (since damp wood is easier to chew).

They play an important role in nature by helping to break down dead and decomposing wood and cycling nutrients. In our ornamental trees, significant damage is rare and often indicates that a tree has other significant damage that is more of a concern than the ants themselves. Therefore, treatment is not usually recommended for the trees themselves, though some may choose to treat if the trees are located in close proximity to wooden structures that can potentially be damaged by these ants.

I’m hoping that this post illuminated some of the interesting and diverse roles that ants play in and around our gardens. More than anything, though, I hope that this inspires you to be observant and to go out and explore some of these interesting and complex associations between insects and plants that we can often see in our very own backyards!

Resources

Ants in Agricultural Systems
https://www.sciencedirect.com/science/article/abs/pii/S1049964420306058
https://royalsocietypublishing.org/doi/10.1098/rspb.2022.1316

Farmer Ants and their Aphid Herds
https://www.mcgill.ca/oss/article/did-you-know/farmer-ants-and-their-aphid-herds

Mound Ants
https://www.canr.msu.edu/news/mound_ants

Ants on Peonies
https://ipm.missouri.edu/MEG/2018/5/antsOnPeonies/

Carpenter Ants
https://www.extension.iastate.edu/news/2009/jun/060503.htm

I thought this would be a fairly straightforward individual to research and write about. But no, talk about a rabbit hole.
Have you ever known someone that makes you ask, “They did what?” or “They’re where?” or “What are they up to now?”
If so, then you’ll recognize the type in this installment of People and Plants.

Friedrich/Frederick Adolph Wislizenus  was a German-born American medical doctor, explorer and botanist. The name Wislizenus traces its etymological roots back to Poland, specifically the town of Wislicza.
Friedrich A. Wislizenus is known for his printed recollections of travels to New Mexico territory and northern Mexico. He was born in Königsee, Germany on May 21, 1810, the youngest of three. The children were orphaned very young and a maternal uncle took them in. After completing “high school” at the Rudolstadt Gymnasium, Friedrich continued his studies at the Universities of Jena, Goettingen and Würzburg. In April 1833 he took a break from his schoolwork by actively participating in a revolutionary uprising against the existing German government. (Another participant of this event was Ferdinand Lindheimer.) The expected groundswell of support from the citizenry didn’t happen while a strong police presence did. In response Friedrich suddenly decided he should leave town.

He wound up in Zürich, Switzerland where he matriculated at the University of Zürich. His studies again suffered a brief interruption when he joined a movement to free Italy from monarchical rule. The expedition was disarmed by Swiss troops before reaching the border. There was nothing for our Friedrich to do but go back to the college from which he graduated in 1834 with high honors in Medicine.
Thereafter he decided to move to Paris to work but found no opportunities, so in the fall of 1834 he sailed for New York to hopefully establish himself in his profession.
By 1837 he had journeyed to Mascoutah, Illinois on the outskirts of St. Louis and was practicing his trade. Finding the practise of a country doctor’s life dull, monotonous, and lacking in remuneration, he relocated to St. Louis in 1839. 

Before settling down to resume his medical career Friedrich decided to make an extended journey into the farthest West. Scraping together his meager savings, he left the banks of the Mississippi in the spring of 1839 as a member of one of the annual expeditions of the Rocky Mountain Fur Company. His travels lead him into the far Northwest to the Wind River Mountains and then over the Rockies. Friedrich eventually reached Fort Hall on the Snake River, near the present site of Pocatello, Idaho, which at the time was the Southernmost trading post of the English who still held Oregon Territory in I839.
That’s a lot of ground to cover in six months.

From Ft. Hall he intended to cross the Sierra Nevadas and wander into California. But this dream was shattered for the lack of a competent guide. So he ventured back along the banks of the Arkansas River to the Missouri border. This voyage proved to be quite an adventure due to the inability of finding facilities, supplies, and the lack of equipment. He finally reached St. Louis in 1840. His record of this journey of almost six months duration was first printed in German in 1840. His son later translated it into English and published it along with a biographical sketch in I9I2. Its observations on the flora and fauna are quite detailed and the Linneaus binomial scientific designations are often included. Topography and geologic findings are also noted along with meteorological reports.

Friedrich resumed his medical practice and soon became involved in various civic activities. He was a regular attendant at the Western Academy of Natural Sciences where he found a kindred spirit in Dr. George Engelmann. The two were to become life long friends to the extent of taking care of the other’s patients when one of them was out of town.
In 1846, finding he could no longer ignore his “itchy feet,” he joined a merchant expedition to Santa Fe in New Mexico Territory. With a goal in mind and the necessary instruments in a horse-drawn wagon, he and an assistant intended to gather information concerning a part of the continent about which little was known.

Upon reaching Santa Fe the intrepid band found the headlines and town chatter were full of news of the Mexican-American War. Despite the situation the group determined to travel south, cross the border, and make it to the state of Chihuahua by September, which they did. Immediately upon reaching their destination the entire company was imprisoned. Not being a man to waste an opportunity, Friedrich put the several months in a secluded mountain village to good use. The enforced stay resulted in collection of notes, observations and sketches concerning the flora, fauna, topography, and weather of northern Mexico. Finally in the spring of 1847 the prisoners were freed by Colonel Alexander Doniphan. Friedrich accepted Colonel Doniphan’s offer of a temporary appointment as surgeon in the U. S. Army and continued with the soldiery to the mouth of the Rio Grande. He then returned to St. Louis via New Orleans before 1847 had ended.

Due to the efforts of Senator Thomas H. Benton, whom he’d become acquainted with, Wislizenus was summoned to Washington, D.C., and requested to publish his recollections, Memoir of a Tour to Northern Mexico in 1846 and 1847 by A. Wislizenus, M.D. This volume corrected many erroneous views of the western country and provided detailed descriptions (with maps and sketches) of the lands near the Rio Grande. The Senate ordered printing of 5,000 copies, which was a lot for the time, for distribution.

Among the trophies brought from his travels were many new plants, both as samples and sketches. These were later studied by his good friend and colleague Dr. George Engelmann who named many of the specimens after Wislizenus.
Dr. Wislizenus also has a lizard named after him. The animal was first documented by Friedrich in Santa Fe, New Mexico Territory.

The next several years saw Friedrich getting married, becoming a father and traveling the world, including Turkey, a visit to his hometown, Panama and finally getting to visit the West Coast of America. He returned to St. Louis in 1852 and spent the rest of his life there. He pursued scientific and civic interests, being one of the founders of the St. Louis Academy of Science and the Missouri Historical Society. He continued to indulge his love of meteorology and botany as long as his failing eyesight would allow. He died in September 1889 and he and his wife are buried on their estate near Kimmswick, Missouri on a high bluff overlooking the Mississippi River.

Dr. Wislizenus’ writings are available here:
https://www.biodiversitylibrary.org/creator/253456#/titles

To see list of plants attributed to Dr. Wislizenus go here:
https://tropicos.org/specimen/Search and type Wislizenus in the Senior Collector box and click on Search.