color shifts

Some of our most common spiders are extremely variable in color. A few spiders can actually change color to match the background. The “flower spider” group of crab spiders are the most famous of these here in Ohio. They get this name from their behavior of waiting in flowers, where they ambush visiting pollinators. For example, the whitebanded crab spiders (Misumenoides formosipes) in flowers sometimes match the color of their ambush site.

white banded crab spider (Misumenoides formosipes) waiting in ambush

white banded crab spider (Misumenoides formosipes) waiting in ambush

 

 

 

 

 

white banded crab spider (Misumenoides formosipes) waiting in ambush

white banded crab spider (Misumenoides formosipes) waiting in ambush

white banded crab spider (Misumenoides formosipes) with a bee fly prey

white banded crab spider (Misumenoides formosipes) with a bee fly prey

In a study of the influence of color on movement between flowers, and success at capturing prey, Alissa Anderson and Gary Dodson demonstrated that crab spiders which matched their background did capture more prey.

By the way, just in case you were wondering, the white band in the name “whitebanded crab spider” refers to the light-colored ridge (carina) that runs across the face below the eyes. The carina is the best way to tell this spider from our other common color-shifter, the goldenrod crab spider (Misumena vatia). The goldenrod crab spider shown below has adopted white coloration to blend in (quite well) well with the queen Anne’s lace in this view.

goldenrod crab spider (Misumena vatia) waiting in ambush on flowerhead of Queen Anne's Lace

goldenrod crab spider (Misumena vatia) waiting in ambush on flowerhead of Queen Anne’s Lace

Other spiders have discrete “color forms” where there is discontinuous variation in color from one form to another. One example of this type of color variation is the triangulate orbweaver (Verrucosa arenata). In this species the cephalothorax, legs, and most of the abdomen are either red, or black. On the abdomen there is a bright triangle-shaped mark that is either white or yellow. Individuals of this spider come in many combinations of these colors.

triangulate orbweaver (Verrucosa arenata) black&white color form

triangulate orbweaver (Verrucosa arenata) black&white color form

triangulate orbweaver (Verrucosa arenata) black&yellow color form

triangulate orbweaver (Verrucosa arenata) black&yellow color form

triangulate orbweaver (Verrucosa arenata) red&white color form

triangulate orbweaver (Verrucosa arenata) red&white color form

triangulate orbweaver (Verrucosa arenata) red&yellow color form

triangulate orbweaver (Verrucosa arenata) red&yellow color form

Other spiders seem to have more continuous variation in color. One candidate for the most common spider in the world is the aptly named “common house spider” (Parasteatoda tepidariorum). This cosmopolitan spider can be found around buildings nearly everywhere. It was just as common outside my office at the University of Sydney in Australia during the 1980’s as it is around the Ohio State University. Here in Ohio, the cephalothorax and legs are usually a deep brown, sometimes reddish brown. The abdomen has a variegated pattern with a base-color that may be pale tan or yellow, or very dark, nearly black.

common house spider (Parasteatoda tepidariorum) dark female

common house spider (Parasteatoda tepidariorum) dark female

common house spider (Parasteatoda tepidariorum) pale female

common house spider (Parasteatoda tepidariorum) pale female

 

 

 

 

 

 

 

 

 

Some individuals have a more red-orange tinge to their dark markings. The brown teardrop-shaped egg cases of these spiders are often found in the webs of adult females.

common house spider (Parasteatoda tepidariorum) with her egg case

common house spider (Parasteatoda tepidariorum) with her egg case

We have many of these spiders on the walls of our house in central Ohio. They capture a wide variety of prey. On July 27th 2014 I photographed this female who had just captured a harvestman (aka daddy-long-legs). Note that she has only one egg case in this photo (one with a distinct pointed end).

common house spider with harvestman prey

common house spider with harvestman prey

Evidently it was a good meal, because by the next day she had two egg cases, having constructed a second one overnight. Amy noticed that she had captured one of the bright green stink bugs that are common in our yard. Here are two of Amy’s photos of her with this prey item.

common house spider capturing green stink bug

common house spider capturing green stink bug

common house spider with green stink bug prey

common house spider with green stink bug prey

After eating this green bug, she made a remarkable color change. She had evidently absorbed enough of the green pigment from her prey to tint her abdomen green. These photos were taken the very next day.

common house spider with remains of green stink bug prey

common house spider with remains of green stink bug prey

Notice that that green stink bug is only a pale lime shadow of its former self… but ms spider has definitely gained some color! (below)

common house spider with green abdomen after eating green stink bug

common house spider with green abdomen after eating green stink bug

common house spider with green abdomen after eating green stink bug

common house spider with green abdomen after eating green stink bug

This diet-related color change has been noticed by many spider workers. Back in 1989 Rosemary Gillespie also demonstrated that diet had a profound effect on the color of the famous “Happy Face” spider of Hawaii. She published a study of this phenomenon in the Journal of Arachnology. You can read this paper here.

In 1998 Theodore Evans and Patrick Gleeson published a paper on a method of exploiting this by feeding dyed termites to captive spiders. The termites were fed paper stained with non-toxic stains. The color was transferred to the spiders when they ate the termites. They used this technique to “mark” the long-bodied cellar spiders (Pholcus phalangioides) with distinctive colors.

Rick Vetter has pointed out in his recent book The Brown Recluse Spider that the abdominal coloration of brown recluse (Loxosceles reclusa) can change dramatically after meals of heavily pigmented prey. In the pictures below, the left photo is what the spider looked like after eating crickets. The photo on the right shows how the same spider appeared after eating two house flies.

Reprinted from The Brown Recluse Spider, by Richard S. Vetter.  Copyright © 2015 by Cornell University.  Used by permission of the author, Richard S. Vetter.  All rights reserved.

Reprinted from The Brown Recluse Spider, by Richard S. Vetter.  Copyright © 2015 by Cornell University.  Used by permission of the author, Richard S. Vetter.  All rights reserved.

Rick’s book describes the biology of the brown recluse and its relatives. He carefully separates myth from reality, and provides useful information about this most notorious American spider. It can be purchased here.

These examples of diet-influenced color change are most obvious in spiders with pale or generally lightly-pigmented abdomens. Often the cephalothorax and legs remain the same because they have a thicker, opaque exoskeleton.

So the moral of this little story is that sometimes “you are what you eat”, or at least you might look like it.

Sources:

Anderson, A.G. and G.N. Dodson. 2015. Colour change ability and its effect on prey capture success in female Misumenoides formosipes crab spiders. Ecological Entomology, 40(2): 106-113.

Evans, T.A. and P.V. Gleeson. 1998. A new method of marking spiders. The Journal of Arachnology, 26: 382-384.

Gillespie, R. G. 1989. Diet-induced color change in the Hawaiian happy-face spider Theridion grallator (Araneae, Theridiidae). J. Arachno!., 17:171-177.

Vetter, R. 2015. The Brown Recluse Spider. Cornell Univ. Press, Ithaca. 186p.

Favorite Bolas spiders!

Bolas spiders are among the most remarkable spiders in the world.   These odd animals are in the family Araneidae, the orb weavers. But unlike the majority of species in this large family, they do not build an orb web. Instead, they hang in a very simple trapeze of silk just below a branch in a tree or shrub.  They prepare for their hunt by spinning one silk line with a droplet of glue at the tip. This is their bolas.   After preparing the bolas, they wait, hanging in mid air below the branch for a moth to come by, holding their bolas line in one of their front legs. When a moth approaches, they toss the bolas to snare the moth.

bolas spider (Mastophora hutchinsoni) hunting with her bolas

bolas spider (Mastophora hutchinsoni) hunting with her bolas

The name “bolas spiders” is a reference to the Argentinean gaucho’s bolas, a line with heavy balls at the end which are used in hunting guanacos (a South American relative of the camel) or rheas (a large flightless bird). If skillfully thrown the line with its balls wraps around the legs of the prey, hobbling them. There is evidence that this unusual hunting tool was invented by the Inca civilization prior to the arrival of the Spanish.

The bolas spider employs her line to catch flying moths. Mark Stowe and Tonia Hsieh have shown that the ball of glue actually has a long thin silk line coiled within.   When the spider tosses her bolas the line unwinds and wraps around the moth. This is a very strong line with adhesive glue, and if successfully deployed, it will hold a large moth desperately trying to fly away.

Watching a bolas spider hanging motionless below her branch, waiting for a moth to fly by close enough to snag, one could be excused for being skeptical that this could ever work. The key to the hunting technique was revealed when Bill Eberhard discovered in 1977 that these spiders catch only male moths. Why males? Because Dr. Eberhard determined that the spider produces a chemical perfume that mimics the sex pheromone of a female moth. The males home in on the odor and fly directly up to the waiting spider. Even after she tosses and misses, the sex-starved male moths continue to approach, presumably still searching for the elusive female moth who isn’t there.

During the day bolas spiders glue themselves to a leaf. Here they sit, with their legs curled up around them. They are fat globular-shaped spiders with subdued colors. Some are brown and white, others with a slight greenish tone. The globular pose and colors make them resemble bird droppings. When disturbed while resting they employ a “stink” defense, the emit an unpleasant odor. This is thought to deter predators.

bolas spider (Mastophora hutchinsoni) resting pose

bolas spider (Mastophora hutchinsoni) resting pose

bolas spider (Mastophora phrynosoma) resting on a leaf

bolas spider (Mastophora phrynosoma) resting on a leaf

bolas spider at rest (Mastophora timuqua)

bolas spider at rest (Mastophora timuqua)

bird dropping, looking a bit like a resting bolas spider

an actual bird dropping, looking a bit like a resting bolas spider

We have been very lucky to have found bolas spiders in our rural Ohio yard. Back in 2001 we found females of the cornfield bolas spider, Mastophora hutchinsoni. Since that time we have found this species hunting in our yard on a number of different years.

bolas spider (Mastophora hutchinsoni) hunting with her bolas

bolas spider (Mastophora hutchinsoni) hunting with her bolas

This August I went out hunting with my headlamp for spiders. I was really hoping to find a bolas spider, because we had not seen one the past few years. I was rewarded with a beautiful adult female hanging from a low branch of a crab apple tree. As I approached, I realized that she didn’t look like the familiar M. hutchinsoni, it was actually a different species of bolas spider! After consulting Herbert Levi’s monograph on this genus, I identified her as an adult female of Mastophora timuqua. This was a very surprising find, the species had been previously known only from Florida and North Carolina, a very long way from Ohio.

bolas spider (Mastophora timuqua) hunting with her bolas

bolas spider (Mastophora timuqua) hunting with her bolas

bolas spider (Mastophora timuqua) hunting with her bolas

bolas spider (Mastophora timuqua) hunting with her bolas

As the summer progressed into autumn I was able to observe the spider hunting on many occasions. Several times I saw moths approach, and observed the spider fling her bolas. Most of these attempts were failures, but once while I was watching she managed to snag a moth. The moth flew in a circle, round and round, held by the silk line until it reached part of the branch and landed. He pulled himself free from the line and escaped.

On one evening I was able to take a photo of the bolas spider before she had completely wrapped her prey. It turned out that this photo was sufficient for John Gilligan to provide me with an identification of the moth (Greater Black-lettered Dart, Xestia dolosa).

bolas spider with fresh capture of Greater Black-lettered Dart (Xestia dolosa)

bolas spider with fresh capture of Greater Black-lettered Dart (Xestia dolosa)

Experimental work has shown that bolas spiders can vary the odor lure that they use to capture moths. They evidently choose from an arsenal of chemical attractants the one that is appropriate for the particular moth species flying that night.

I even tried to shoot video of the hunting bolas spider. My efforts were rewarded with a few short video segments of her hunting. The first video shows her spinning her bolas, pulling out silk and glue to fashion her bolas.  This part takes quite a while, if you stick with it she eventually re-positions herself, holding the completed bolas below. Near the end of this segment she tosses it at a moth, but misses.

Finally after many fruitless evening video shoots, I secured a segment with a successful capture and wrap. This is a five minute video, so you will have to hang in there to see the whole show. At first she misses, but then… success! Beware this is a very violent capture. It is a real testament to the strength of the silk snare. Eventually you will see her approach the wildly spinning moth, deliver a bite, and back off.  Soon you can see the venom take its effect and the moth stops struggling. Finally she returns to wrap her prize.

For the next few weeks she would fatten up on moths each night. Sometimes I was able to find the empty husk of a moth, wrapped mummy-like in a silken shroud, below the spider on the ground.

Mastophora timuqua wrapping a moth prey

Mastophora timuqua wrapping a moth prey

"mummy" of a moth, having been wrapped and discarded by bolas spider

“mummy” of a moth, having been wrapped and discarded by bolas spider

On a few nights I saw the bolas spider hanging with her legs spread, but without a bolas. Perhaps she was still emitting her pheromone lure because on at least two occasions I saw moths approach her in this pose. I never saw her capture a moth without a bolas, so I don’t know for sure if this is what she was doing.

bolas spider Mastophora timuqua hanging in mid air

bolas spider Mastophora timuqua hanging in mid air

The bolas spider stayed on the same branch for weeks. Even after very heavy rain and wind, she remained. On the early morning of the 9th of September, Amy noticed that she was building an egg case. She carefully attached it to the branch, walking around the case and branch laying down many layers of silk to form a sort of strap.

bolas spider (Mastophora timuqua) egg case

bolas spider (Mastophora timuqua) egg case

After laying eggs and constructing the silken case, the spider appeared shrunken. The next night she was hunting again.  After a couple of weeks of meals she was back to her plump self.  After her third egg case, she was visibly wrinkled.

Mastophora timuqua completing her third egg case, she's looking pretty wrinkled

Mastophora timuqua completing her third egg case, she’s looking pretty wrinkled

After laying this third egg case, the spider appeared very gaunt. She hung from the end of her branch, listless. This is the end of her annual cycle, and like most orb-weaving spiders, she would not survive the hard frosts to come. She was remarkably successful to grow to adulthood and produce three egg cases. We can only hope that these will yield a little army of bolas spiderlings next spring.

Bolas spiders have lots of other interesting tricks. For example, sometimes they use a passive bolas technique, spinning a horizontal line and hanging several bolas’ below it.

bolas spider (Mastophora hutchinsoni) with silk line and four hanging bolas lines

bolas spider (Mastophora hutchinsoni) with silk line and four hanging bolas lines

As if all of this wasn’t peculiar enough, adult male bolas spiders are dwarfs. They are very tiny compared to the female. The males mature very early, some even mature while in the egg case and emerge as adults. In other species they molt to maturity very soon after leaving the egg case. As a result they are tiny, like most young spiderlings. In contrast, the females must grow and molt many times to achieve adult size. In the illustration below a female of Mastophora cornigera is shown with a male to the same scale. This illustration is by Steve Buchanan.

Mastophora cornigera, female on left, male on right painting by Steve Buchanan

Mastophora cornigera, female on left, male on right, painting by Steve Buchanan

Recently I was perusing images of bolas spiders (Mastophora) on one of my favorite web sites (bugguide.net).  I found a series of remarkable images of a female Mastophora phrynosoma accompanied by an entourage of little males.  The photos were posted by one of the many volunteer contributors to the bugguide site, Matt Coors.  Matt found the spider in August of 2014 near Cincinnati, Ohio.  Matt is an artist and you can see some more of his photos and samples of his art here.

These photos of adult males with a female of any species of Mastophora are quite rare.

Mastophora phrynosoma with an entourage of little males, photo courtesy of Matt Coors

Mastophora phrynosoma with an entourage of little males, photo courtesy of Matt Coors

Mastophora phrynosoma close-up view of a male, photo courtesy of Matt Coors

Mastophora phrynosoma close-up view of a male, photo courtesy of Matt Coors

There are a total of 50 species in the genus Mastophora, currently known only from the new world.  Other spiders, classified in different genera, with similar pheromone mimicry hunting behavior are found around the world. Of the members of Mastophora, only 15 species have been found in North America north of Mexico, and only 5 are known for Ohio.

For more information about bolas spiders and Steve’s illustrations of a few other species and their distinctive egg cases, you can consult Common Spiders of North America, plate 7 and pp. 94-96.

References:

Eberhard, W. 1977. Aggressive chemical mimicry by a bolas spider. Science, 198: 1173-1175.

Levi, H.W. 2003. The bolas spiders of the genus Mastophora (Araneae: Araneidae). Bulletin of the Museum of Comparative Zoology, 157(5): 309-382.

 

Halloween Spider

The Marbled Orbweaver (Araneus marmoreus) is one of the most common large orb weaving spiders in North America. It is particularly abundant in Ohio. Even so, many people here never notice them. I believe that this is because they live in wooded areas, typically come out only after dark, and hide in a retreat during the day.

Marbled Orbweaver in her retreat

Marbled Orbweaver in her retreat

This species is extremely variable in color and pattern. Here is Steve Buchanan’s painting of some color forms of the species from plate 9 in Common Spiders of North America:

various color forms of Marbled Orbweaver

various color forms of Marbled Orbweaver

The most common color forms encountered here in Ohio are the yellow and orange varieties. Like most large orbweavers, the Marbled Orbweaver lives less than one year. Young emerge from the egg case in the spring. At that time they are tiny and inconspicuous. By early summer they have grown to small juveniles (1/8 to 1/4 inch body length), and are typically cream or pale yellow with little pattern. By mid summer they are large and well marked. If you encounter one in its web at that time of year, they bear a conspicuous pattern on the abdomen.

young female Marbled Orbweaver in her web

young female Marbled Orbweaver in her web

Marbled Orbweaver in her web

Marbled Orbweaver in her web

Marbled Orbweaver (Araneus marmoreus) female

Marbled Orbweaver (Araneus marmoreus) female

This species builds a beautiful orb-shaped (circular) web low in a tree or herbaceous vegetation near the ground. Most individuals re-build their web every evening. Sometimes they replace only the sticky spiral portion. This difference probably depends upon how much the web is damaged by the previous night’s hunting activity. From the center of the web (the hub) there is a taut “signal line” that extends into the retreat. The spider often stays in the retreat with one or more legs touching the signal line, only emerging when a prey item becomes entangled in the web. She detects the presence of the prey via the signal line which transmits the vibrations made by the struggling prey. It only takes her a moment to rush out to the web, find the prey, and bite. The spider often bites insects on their underside. This ensures that the venom will paralyze the victim quickly because the central nerve cord of insects runs along the midline there.

web of Marbled Orbweaver

web of Marbled Orbweaver

Marbled Orbweaver biting a cricket on its underside, shot in captivity

Marbled Orbweaver biting a cricket on its underside, shot in captivity

I often use a simple vibrator (inexpensive dental tool) to lure spiders out of their retreat. When she comes out and finds no prey item, she quickly retreats.

a small dental tool that makes an excellent vibrating "spider lure"

a small dental tool that makes an excellent vibrating “spider lure”

Marbled Orbweaver lured out of her retreat

Marbled Orbweaver lured out of her retreat

female Marbled Orbweaver climbing back into her retreat

female Marbled Orbweaver quickly climbing back into her retreat

In the summer you may also encounter a male Marbled Orbweaver. These are leggy beasts, with a relatively small abdomen. After achieving maturity, the males spend their short lives searching for females. They quit building capture webs and wander through the vegetation, following pheromone scent trails to females.

Marbled Orbweaver adult male

Marbled Orbweaver adult male

For me one of the fun natural events in Ohio every October is the appearance of “Halloween Spiders.” These large, fat, bright orange spiders seem to appear on cue as the spooky holiday approaches. In fact, these are the orange color form of the Marbled Orbweaver. I’ve recently discovered that the very same individuals that have the typical yellow abdomen in summer, turn orange in October. This may correspond to the changing leaf colors. Many spiders, most famously the flower crab spiders, can change their color to match their background, and thus remain camouflaged. The odd thing in this case is that Marbled Orbweavers are often conspicuously colored, not camouflaged at all, as anyone can see from the other photos in this post.

Marbled Orbweaver in her retreat

Marbled Orbweaver in her retreat

orange color form of Marbled Orbweaver in her retreat

orange color form of Marbled Orbweaver in her retreat

"Halloween Spider" an orange color form of Marbled Orbweaver

“Halloween Spider” an orange color form of Marbled Orbweaver

underside of Marbled Orbweaver

underside of Marbled Orbweaver

These fat orange spiders are pregnant females, their abdomens swollen with hundreds of eggs. Sometimes people find them walking on the ground, driveway, or patio deck. In late October, a grape-sized bright orange spider conjures up the image of a miniature pumpkin, and I have received many excited email messages about them over the years. Fortunately I can re-assure the correspondent that this is merely a harmless female spider searching for a good place to lay her eggs. Perhaps this is the reason for the camo color, because walking through the fallen leaves in the daytime is a real departure from their summer reclusive behavior. These females will die soon after laying their eggs, often coincident with the first hard frosts of autumn.

very odd behavior

The other day as I was walking from the garden shed towards our house I surveyed some of our milkweed plants, hoping to find a Monarch Butterfly caterpillar. We have seen only a few caterpillars this year. That is better than last year, when I don’t remember seeing any in our yard. Anyway, as I checked the milkweed leaves I noticed a familiar beetle, one of the colorful checkered beetles (members of the family Cleridae). What caught my eye about this beetle is that it was evidently feeding on a patch of white gelatinous material, possibly milkweed sap.

checkered beetle Enoclerus rosmarus

checkered beetle Enoclerus rosmarus

As I watched, it was approached by a spider, a little (about 1/4 inch long) male Tutelina elegans. Then something really odd happened, the spider hopped on top of the beetle. He wasn’t trying to capture the beetle, and didn’t attempt to bite it. He took the position typically adopted by jumping spider males when mating! He reached over the back of the beetle, and rubbed the beetle’s belly with his palp. Then he switched position to do the mirror-image behavior on the other side. This is the typical mating behavior in jumping spiders. If this had been a female spider, the male’s palp would have been inserted into her reproductive openings, right and left one at a time. Below is an illustration from B.J. Kaston’s classic (1948) guide Spiders of Connecticut. I’ve reproduced, with permission of the publisher, the illustration of a pair of Phidippus clarus (a common jumping spider). In this diagram the male is in black, the female in outline. This is figure 2010 drawn by Elizabeth Haban Kaston.

mating position of the jumping spider Phidippus clarus (from Kaston's Spiders of Connecticut)

mating position of the jumping spider Phidippus clarus (from Kaston’s Spiders of Connecticut)

Below are several photos of the odd behavior of that male Tutelina and its beetle “friend.” I guess I can’t decide which is more peculiar, the fact that the spider is trying to mate with a beetle, or that the beetle seems not to react at all!

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Tutelina elegans male on top of a checkered beetle

Note that this male spider is missing his left front leg. This loss may have severely limited his ability to attract a female. In this species leg waving is an important part of the courtship dance. Here is a close-up picture of a male searching for a female while waving his dramatic tufted legs.  Check out the funky tufts on his head too!

adult male Tutelina elegans, in captivity waving his legs

adult male Tutelina elegans, in captivity waving his legs

Throughout all of this the beetle remained motionless. It is hard to imagine what it might have been thinking. I’m tempted to speculate that the male spider’s odd behavior was influenced by his missing leg and consequent inability to successfully court a real female spider.

The actual female of this species is a beautiful iridescent green, to our eyes it looks nothing like the checkered beetle. I wonder if there might be more resemblance in the vision of a jumping spider. This possibility seems remote however, because jumping spiders are renown for their high-acuity color vision, an unusual feature among spiders. Of course we don’t know what is going on inside their brains. Below are two photos of female Tutelina elegans.

Tutelina elegans female

Tutelina elegans female

Tutelina elegans female

Tutelina elegans female

Normally these little iridescent green jumping spiders are found running among the herbaceous vegetation. The adult males seem to spend all of their time searching for females, waving their legs while they search. Here are a few of photos of males and females Tutelina from our yard.

Tutelina elegans female

Tutelina elegans female

Tutelina elegans female, she can wave her legs too!

Tutelina elegans female, she can wave her legs too!

Tutelina elegans female

Tutelina elegans female

Tutelina elegans male searching for a female, waving his legs

Tutelina elegans male searching for a female, waving his legs

Tutelina elegans male

Tutelina elegans male

This elegant iridescent green spider is actually very common in much of eastern North America. You can find more information about it in Common Spiders of North America (p 205, plate 63).  I thank George Keeney (Ohio State University) for identifying the beetle Enoclerus rosmarus.

It’s that time of year again

It is that time of year again, I’m starting to receive email queries about large brown spiders in webs.   Typical questions ask about identification and whether or not the spider in question is “dangerous.” The messages sometimes include helpful photographs, often taken with mobile phones. These snapshots are usually good enough that I can recognize the spider as Neoscona crucifera (aka arboreal orbweaver or variable orbweaver).

spider in web at night

arboreal orbweaver (Neoscona crucifera) in her web

This species is interesting for a number of reasons. It seems to have adapted well to human-altered habitats. It is common at the edges of woods, orchards, suburban yards and even building webs directly on houses and other buildings. This species is common, even abundant in the east, and has recently expanded its range and abundance in the south and west.

distribution map of Neoscona crucifera in North America, north of Mexico

distribution map of Neoscona crucifera in North America, north of Mexico

The webs of this spider are often quite large, with a frame of 3-5 feet and an orb with a diameter between 1 and 1.5 feet. The webs may be built near windows or other light sources. I suspect that they build in such situations because of the abundance of potential prey insects attracted to lights at night. During late summer and autumn search for these spiders building their webs just after dusk. If you time it just right, you can catch them in the act. The amazing construction dance of a large heavy-bodied orbweaver is always a wonder to behold. Pay attention to the leg movements, that is how she uses her body dimensions to gauge the spacing of the spiral sticky strands, and of course the web becomes larger as she grows. After she is done, she will typically hang, head down, at the hub or center of the web for most of the night. Typical prey are large moths, beetles, and other night-flying insects. Sometimes the spider will remain in the web after sunrise.

Like all of the orbweavers found in North America, Neoscona crucifera is considered harmless to humans and pets. They are shy spiders and will either rapidly retreat, or perhaps drop from their web if disturbed. In my experience they do not bite humans. Like most spiders, they are venomous, but they employ their venom against insect prey.

One dramatic feature of the members of the orbweaver group (Family Araneidae) is the pattern on the belly (ventral side) of the abdomen. Most of them have a central black spot, usually nearly rectangular. At each corner of the black area are a series of pale (white, cream, yellow) spots. These spots can be shaped like a comma, or nearly round. The pattern of a black patch with such conspicuous spots is often mentioned by people when they see this spider for the first time. Sadly, they are not too useful in identification because some variant or another occurs in many species. For example, each of the four members of the genus Neoscona in Ohio include this feature.

Neoscona crucifera female (underside)

Neoscona crucifera female (underside)

Immature individuals of this spider emerge in the late spring, but they don’t become large enough for most people to spot until summer. By late summer they are hard to miss. The individuals that are most often noticed are females, which can be large. Some have a body length of about 20mm (3/4 inch) with a leg span of 1.5 to 2 inches. One of the most remarkable things about these spiders is how extremely variable they are. Some are plain, with a faint pattern on the abdomen, or no pattern at all. Others can show a dramatic cross-shaped mark on the abdomen, with or without a series of dark markings. Such variation doesn’t seem to be geographic, instead it is polymorphism that can sometimes be observed among several individuals in one locality. In addition to variation in pattern, the base color varies from orange, through reddish brown to a plain brown or tan.

Neoscona crucifera female (with prey)

Neoscona crucifera female (with prey)

Neoscona crucifera female

Neoscona crucifera female

Neoscona crucifera female

Neoscona crucifera female

Neoscona crucifera female

Neoscona crucifera female

The femora (large segments of the legs nearest the body) are usually orange or red in color. This can be seen when the spider has its legs completely spread, and may not show if the spider is in its defensive crouch.

Neoscona crucifera with her reddish-colored femora (largest leg segments)

Neoscona crucifera with her reddish-colored femora (largest leg segments)

The males can also be variable in color and pattern. They typically have a smaller body than the females, with proportionately longer legs. After reaching maturity, the males abandon their webs and wander in search of females. Perhaps because of their smaller, slender body, or leggy look, the spines on their bodies seem more prominent. These wandering males may accidentally enter houses. I have records of wandering adult males here in Ohio between 11 August and 11 September.

male Neoscona crucifera resting

male Neoscona crucifera resting

male Neoscona crucifera searching; note that he has lost one of his legs

male Neoscona crucifera searching; note that he has lost one of his legs

By the late autumn, the females have mated and are fat with eggs. They will construct one or more silken egg cases containing hundreds of eggs. These eggs survive through the winter and emerge once the weather becomes consistently warm in late spring. My records of adult females in Ohio extend from 15 June through 2 December. Most will perish with the first hard frosts in October and November.

You can find more information (p. 99) and illustrations of this species (Plate 15), and its relatives in my Common Spiders of North America.