Month: January 2025

Even though some may not be fond of them, we understand that most spiders are beneficial, excellent predators of arthropod pests and are extremely interesting organisms. Gardeners are often really enthusiastic about this group of arthropods and enjoy observing them in outdoor landscapes, usually at a comfortable distance. There are some of us who enjoy the company of these creatures in closer proximity, even indoors and as pets (myself included).

Writing a post about spiders has long been on the back of my mind, and a topic that has been requested multiple times. So as I sit in front of my fireplace on this snowy Montana evening, thinking back to the several spiderwebs speckled in between my wood pile, I thought that this month would be the perfect time to do some spider research. For this post I will be focusing on the outdoor spiders that we can commonly find in our gardens: who they are, what they do, and how we can make more of a hospitable environment for them.  As usual I will caveat this by saying spiders are a broad group, and since I can’t exhaustively cover them in the scope of this post I will share resources for you to learn more at the end.

Types of Spiders in the Garden

Spiders are arachnids (class: Arachnida) and share this category with scorpions, ticks, and mites. They fall within the order Araneae, containing more than 50,000 species across 134 different families, making them the largest group of arachnids in terms of species diversity. They have 2 body segments, 8 legs, chelicerae with fangs, and spinnerets that can produce silk. Although all spiders can produce silk, not all of them make webs. Nearly all spiders are venomous (except for 2 families which lack venom glands) however, most spiders either do not bite humans, do not have venom potent enough to negatively impact us, or fangs capable of penetrating our skin. Spider venom is primarily used to immobilize and subdue their prey which are often smaller arthropods like insects. There are a few spiders of medical importance (as we know) who can be found in close proximity to humans, and some people can have an allergic reaction to spider venom (like with many insect venoms). Most spiders are carnivorous, feeding on small arthropod prey, and some of them supplement their diet with plant products like nectar and pollen. One species (Bagheera kiplingi) is known to be primarily herbivorous. For the most part though, spiders are amazing generalist predators most of which are not dangerous to humans and all of which will not seek you out and hunt you down (despite what some exaggerated spider-related media and tropes may claim).

Jumping Spiders

Arguably the cutest group of spiders around, jumping spiders (family: Salticidae) can sometimes even convince the most spider averse people to take a second look in appreciation. Jumping spiders comprise the largest family of spiders, containing more than 6000 species worldwide. These often brightly colored critters with distinctly large eyes do not spin webs, but actively hunt prey, often during the daytime with their excellent vision. Aptly named for the large leaps they can make while hunting for prey or escaping threats, they can be extremely entertaining to watch around the garden. They can use their silk to make small insulated shelters under leaves, bark, or between rock cracks. They also produce compounds like glycol and other proteins which act like an antifreeze, allowing some of them to remain active in colder and even freezing temperatures.

Orb-Weavers

The characteristic mascot of spiders in the garden, orb-weavers (family: Araneidae) build the very familiar large, circular spider webs that we all can easily picture. These magnificent builders lay in wait of prey that flies or crawls onto the sticky parts of their webs. After biting their prey to immobilize it, they proceed to wrap them in silk. Most of them are active at dusk and will rebuild their webs each day.

Wolf Spiders

Wolf spiders (family: Lycosidae) are another group of non-web spinning spiders known for their active hunting abilities. Some will wander around the ground, searching for prey, while others wait in burrows for an unsuspecting victim to walk by. These hairy grey, black, and brown spiders have excellent eyesight and many of them are primarily nocturnal hunters. Females lay their eggs in a silk sac and actively protect them by carrying them around. Once they hatch, the mother will carry these spiderlings (in some cases, over 100 of them) on her back, which is quite a spectacular sight to behold.

Ground Spiders

Ground spiders (family: Gnaphosidae), similar to wolf spiders, are nocturnal hunters who use their quick speed to hunt down and chase after prey. They use their sticky silk to entangle their prey, immobilizing them. This hunting behavior allows this group of spiders to target prey larger in size than themselves. During the day they can be found in silk shelters. A really cool group in this family includes the ant-mimicking ground spiders (genus: Micaria). The first time I spotted this spider under a rock in Kentucky, all of my entomological instincts were telling me that it doesn’t quite look like an ant. Upon closer observation, the 8-legs gave it away (but not before our whole group was thoroughly impressed by its ant-like appearance).

Crab Spiders

These sometimes brightly colored and distinctly shaped spiders (family: Thomisidae) can also be found worldwide. They are called crab spiders because of the way that their two pairs of front legs (which are longer than the rest of their legs) are positioned, in addition to their sideways and backwards movement which can be crab-like. These are another group of non-web making spiders which act as ambush predators. Sometimes referred to as “flower spiders”, they can be found perched on a flower, waiting for a visitor to stop by for some nectar before they pounce.

Lynx Spiders

Lynx spiders (family: Oxyopidae) are another group of ambush hunters that target prey species found on plants. Similar to crab spiders, some species can also capture pollinators while they patiently await them on flowers. Due to their often green and brown coloration, they can camouflage themselves in plants, making hunting for prey easier. Species in this group are also known to be important for biocontrol in agricultural systems.

Funnel-Weavers & Grass Spiders

Funnel-weavers (family: Agelenidae) are another cosmopolitan group of spiders known for their very quick speeds and their unique webs. Named for the structure of their webs, which looks like a flat sheet that tapers into a funnel-shape, these spiders lay in wait for prey that walk across these sheets, triggering vibrations that cause the spider to ambush them. Although these webs are not sticky (unlike sections of orb-weaver webs), they do contain a lot of silk fibers that can entangle their prey. Once the prey have been subdued by a quick bite, the funnel-weaver grabs their tasty meal and retreats back into the safety of its funnel. Not to be confused with funnel-web tarantulas, these spiders can create their funnel-shaped webs in leaflitter, on soil, or in grass. This family includes grass spiders and also the common house spiders. Some species may seek refuge indoors during the winter time (an example being Hobo spiders), which can sometimes be a nuisance for people.

Sheet Weavers

Sheet weavers or money spiders (family: Linyphiidae) are a group of very tiny spiders, containing over 4700 species worldwide (making them the second largest family after jumping spiders). Although they are very widespread, their small size makes them easy to miss. Many species of Lyniphiids are considered excellent biocontrols of small soft-bodied arthropod pests such as aphids.

Harvestmen

Although Harvestmen (Order: Opiliones) may greatly resemble them, they actually aren’t spiders, even though they are arachnids. They do have 8 legs, but only have one body segment, no fangs or venom glands, and do not produce any silk. They are sometimes referred to as daddy-longlegs, not to be confused with daddy-longlegs spiders, which are in fact spiders in the family Pholcidae. There are many tall tales associated with this group of spiders so to learn more about them check out the resources. Harvestmen prefer moist environments such as caves, leaflitter, and under logs. They are omnivores and opportunistically feed on decaying vegetation, carrion, animal waste, and small arthropods. They can also aggregate together to retain moisture (which can be quite a sight to behold).

Benefits of Spiders

Due to their carnivorous diets, diverse hunting behaviors, and widespread distributions, spiders are excellent beneficial organisms which can reduce pest populations in a wide variety of landscapes. They are also well-known as naturally-occurring biological controls in many agricultural and horticultural systems. Several studies have been conducted which demonstrate the benefit of a variety of groups of spiders in these systems. Spiders can reduce populations of common groups of pests including caterpillars, aphids, leafhoppers, planthoppers, and beetles.

Many groups of spiders can be found in agricultural systems. An analysis by Young and Edwards (1990) demonstrated the presence of over 600 spider species spanning 26 families found in 9 specific field crops in the United States. According to their analysis: 5 spider families comprised the majority found in field crops including Salticidae [jumping siders], Linyphiidae [sheet weavers], Araneidae [orb-weavers], Theridiidae [tangle-web spiders], and Lycosidae [wolf spiders] (Young and Edwards, 1990). A study conducted by Akhtar et al. (2024) showed 45 spider species spanning 13 families in maize crops in the Punjab region of Pakistan. The families that made up the majority of these species included Araneidae [orb-weavers], Lycosidae [wolf spiders], and Salticidae [jumping spiders] (Akhtar et al., 2024). These are just a couple of examples of studies that have been conducted, though there are many more you can find!

Several studies have also demonstrated that presence and density of spider populations resulted in an increase or improvement in crop production. A meta-analysis conducted by Michalko et al. (2019) evaluated 58 studies conducted on the impact of spider density on crop performance and found an overall positive result. Agricultural pest insects were suppressed in situations of higher spider density in 79% of cases. Their efficacy in biocontrol varied depending on the type of crop, but was highest in rice, grape, cabbage, and wheat systems (Michalko et al., 2019).

As more research continues to be conducted, I am sure that we will find many more instances in which spiders improve crop productivity through the suppression of common pests.

Protecting and Conserving Them

All of these studies show that the presence of beneficial organisms like natural enemies can be important natural biological controls which can assist us in having a more productive garden (whether the scale of production is large or small). As such, thinking about protecting and conserving these awesome generalist predators is in our best interest.

Implementing practices that can reduce negative impacts on spiders, and creating a landscape that favors them can have wonderful benefits for our gardens. Much of this can also be intuitively considered when you think about the biology and hunting behavior of these groups of spiders. A study conducted by Mashavakure et al. (2019) on the impact of farming practices on spiders in southern Africa showed a variety of common trends which can be adapted for gardens of different scales. In this study, they showed that the two factors that had the largest impact on spider populations were tillage and mulching (Mashavakure et al., 2019). Practices with minimum tillage had highest populations of Lycosidae [wolf spiders], Gnaphosidae [ground spiders], and Salticidae [jumping spiders] (Mashavakure et al., 2019). Plots that had the lowest mulching levels also had the highest populations of Gnaphosidae [ground spiders] and Thomisidae [crab spiders] (Mashavakure et al., 2019).

Structural complexity and diversity of vegetation is another way that you can conserve and increase beneficials in the landscape (including spiders). Having a variety of plants of different sizes and maintaining this habitat year-round can provide shelter, hunting spaces, and overwintering sites for spiders in the home landscape. In addition, reducing practices that can harm beneficials including practicing IPM and reducing the use of broad spectrum insecticides, also goes hand in hand with creating more habitat for spiders.

I hope this post illuminated some of the diversity and beauty of our favorite 8-legged garden companions. Even if some may not want to snuggle up to them, we as gardeners can always appreciate the importance of these amazing creatures in our landscapes.

Resources:

Daddy-longlegs myths: https://spiders.ucr.edu/daddy-long-legs

Overview of Spiders in Agriculture: https://vegcropshotline.org/article/insect-spotlight-spiders-an-overview-of-their-role-in-agricultural-systems/

Young, O. P., & Edwards, G. B. (1990). Spiders in United States field crops and their potential effect on crop pests. Journal of Arachnology, 1-27.
https://www.researchgate.net/profile/G-Edwards/publication/256082787_Spiders_in_United_States_field_crops_and_their_potential_effect_on_crop_pests/links/00463539065408dc43000000/Spiders-in-United-States-field-crops-and-their-potential-effect-on-crop-pests.pdf

Akhtar, N., Tahir, H. M., Ali, A., Ahsan, M. M., & Abdin, Z. U. (2024). Assessment of Biodiversity and Seasonal Dynamics of Spiders in Maize Crops of Punjab, Pakistan. Journal of Asia-Pacific Biodiversity.
https://www.sciencedirect.com/science/article/pii/S2287884X2400061X

Mashavakure, N., Mashingaidze, A. B., Musundire, R., Nhamo, N., Gandiwa, E., Thierfelder, C., & Muposhi, V. K. (2019). Spider community shift in response to farming practices in a sub-humid agroecosystem of southern Africa. Agriculture, Ecosystems & Environment, 272, 237-245.
https://www.sciencedirect.com/science/article/pii/S0167880918304821

Once again we wander down the path of botanical history.

George Julius Engelmann was a botanist, physician, and meteorologist, but is remembered primarily for his botanical monographs. George, also known as Georg, was born Feb. 2, 1809 in Frankfurt am Main, Germany, the oldest of thirteen children, nine of whom reached maturity.  Unusual for the time, his parents established and ran a successful school for young women there in Frankfurt.

Like most privileged young men of the time, George attended gymnasium. He started to take an interest in plants when he was 15 but was also keen on history, languages, and drawing. With the help of a scholarship, 1827 found him studying sciences at the University of Heidelberg. In 1828 young Engelmann, being embarrassed by his participation in a recent student political demonstration, decided to transfer to the University of Berlin for a couple of years. He then moved on to the University of Würzburg where he graduated in 1831 as a Doctor of Medicine. With shades of things to come, his dissertation for the medical degree was more related to botany than to medicine. It was devoted to morphology, the structure and forms of plants, and was illustrated with five plates of figures drawn and transferred to the lithographic stone by Engelmann himself. It was published in Frankfurt in 1832 under the title of De Antholysi Prodromus.

Spring and summer of 1832 found him in Paris where he was leading, ” a glorious life…in spite of the cholera,” but changes were on the horizon. His uncles wanted to make land investments along the Mississippi River and enlisted him to be their agent. In September of that year George sailed from Bremen to Baltimore and made his way to family already living in Illinois near St. Louis. For the next three years, to get a better lay of the land which he’d been hired to sell, he made many long horseback journeys alone through southern Illinois, Missouri, and Arkansas. While he did use his recently acquired regional knowledge in his new job, his botanical notes waited to be used in the future.

Tiring of the land agent role by late 1835, he moved to St. Louis to start a medical practise. Apparently needing more to do, in 1836 he founded a German newspaper called Das Westland. It contained articles on life and manners in the United States and was widely read and appreciated in the United States and Europe. Four years later his medical practise was well established and he’d earned enough money to make a trip back to his hometown. There he fell in love, got married, and the newlyweds then returned to America. When they landed in New York City Engelmann met Asa Gray, already a well known American botanist. A close friendship developed between the two which was ended only by death. 

Eventually Engelmann’s medical practise in St. Louis became so successful he no longer needed to keep office hours: he simply saw patients in his study. This allowed him to take long vacations and devote more time to his preferred botany and biology studies. An 1842 monograph on dodders, A Monograph of North American Cuscutinae, had established his reputation as a botanist. He was one of the earliest to study Vitis (the grape species) of North America; nearly all that is known scientifically of these plants is due to his investigations. One of his most economically important discoveries was of the immunity of the North American grape to the plant pest Phylloxera, which became very significant later in the century during The Great French Wine Blight.

In the 1870s French vineyards came under attack by Phylloxera vastatrix which feeds on grape vines roots. Growers observed that certain imported American vines were resistant to the insect’s feeding habits. The French government dispatched a scientist to St. Louis to consult with the Missouri state entomologist and Engelmann, who had studied American grapes since the 1850s. Engelmann verified that certain living American species had resisted Phylloxera for nearly 40 years. Additionally it was found that Vitis riparia, a wild grape of the Mississippi Valley, did not cross pollinate with less resistant species which was the cause of previous growing failures. Engelmann arranged to have millions of shoots and seeds of V. riparia sent to France which eventually provided Phylloxera resistant rootstock and saved the French wine industry.

Other difficult plant groups Engelmann studied include cacti, conifers, mistletoes, rushes, and yuccas. In 1859, he published Cactaceae of the Boundary which studied cacti on the United States/Mexico border. A unique aspect of Engelmann’s cacti studies is he established, for the first time, the classification of these plants based on floral, fruit, and seed characteristics.  The source he referenced for this was Dr. Wislizenus’ Expedition from Missouri to North Mexico. Engelmann eventually published two books on cacti, both of which are still valued references. Other monographs he published are Notes on the Genus Yucca (1873) and Notes on Agaves (1875). The latter was illustrated with photographs, which is something we tend to expect now but was quite forward thinking at the time.

In addition to his writing, both alone and in collaboration with others, Dr. Engelmann was also a founding member of the St. Louis Academy of Sciences and the National Academy of Sciences. He was instrumental in the establishment of the Missouri Botanical Garden by encouraging Henry Shaw, a wealthy St. Louis businessman, to develop his already extensive gardens to be of scientific as well as public use. What was then called “Shaw’s Gardens” eventually became the Missouri Botanical Garden. Engelmann’s botanical collection, which contains the original specimens from which many western plants have been named and described, was given to the Missouri Botanical Garden. This gift of almost 100,000 specimens led to the founding of the Henry Shaw School of Botany at Washington University in St. Louis, where an Engelmann Professorship of Botany was established by Shaw in his honor. His legacy also lives through the many plant species named in his honor, including Engelmann oak (Quercus engelmannii), Engelmann spruce (Picea engelmannii), Apache pine (Pinus engelmannii), and Engelmann’s quillwort (Isoetes engelmannii).

Engelmann died in 1884. He was interred next to his wife, who passed away in 1879, in the Bellefontiane Cemetery in St. Louis.

The botanical works of the late George Engelmann, collected for Henry Shaw, esq. /Ed. by William Trelease and Asa Gray.
https://archive.org/details/mobot31753000060878

PPT on digitizing Engelmann’s collection
https://www.slideshare.net/slideshow/digitizing-engelmanns-legacy-4745573/4745573