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Hyptiotes the triangle weaver

Posted on October 25, 2021 by richardbradleyOctober 25, 2021

In a woods near you there may be an amazing little spider called Hyptiotes. This spider (and relatives in the same genus around the world) are famous for constructing a triangle-shaped web, hence their common name “triangle weaver.”

Hyptiotes cavatus (the triangle spider) in her hunting pose, holding her web under tension.

Hyptiotes tending to her web among the dead branches of a shrub.

The web is unusual for many reasons but most folks look at it and see what appears to be a pie-slice out of an orb web. There are radial lines converging on a point, and there are parallel spaced silk lines forming a pattern that does look like part of a typical orb. But these webs are different. They have been built by a spider that uses cribellate silk, not glue-laden silk to entrap prey. The cribellate silk is sticky in a completely different way. It has tiny fluffy silk lines surrounding central lines. The fluff is so fine that when an insect or other potential prey brushes against it, they adhere to the hairs and spines on the prey in a way similar to the function of a Velcro © strip.

Here is a photo of the triangular sticky portion of a Hyptiotes web, made visible by a dark cardboard background after I misted it with water.

The triangular portion of Hyptiotes web.

That isn’t the most amazing feature of the triangle weaver’s web. This tiny spider (they are only about the size of a grain of rice) holds the entire web structure under tension, pulling her line taut with her back legs and gathering the slack in a small ball of silk that lies on top of her legs. If a fly, or other potential prey, strikes the web and is caught in the sticky cribellar line, the spider rapidly releases the tension. This causes the spider to jerk forward as the web partly collapses. The collapsing web further entangles the prey. She may use this technique several times to effectively snare the victim.

Here is a close-up view of Hyptiotes as she is holding her web under tension, you can notice the little pile of slack silk line near her back legs. In this case there is also a small ball of slack near her front legs. I’ve added arrows to highlight these little bundles.

Hyptiotes holding web under tension with extra line in bundles near rear and front legs.

A couple of weeks ago I noticed that one Hyptiotes had built her snare between a thin dry twig I had laid across the arms of a lawn chair and the body of the chair. This is the first time I’ve found Hyptiotes in my yard, and also the first time I’ve ever seen one build a web away from a woods or forest.

Hyptiotes holding her triangular-shaped web under tension.

Hyptiotes holding web under tension with extra line in bundles near rear and front legs

This presented an opportunity too good to miss. I decided to take some close-up photos and also see if I might be able to shoot some video of her in action. The photos were much easier to get. Here are two that feature this amazing little spider.

Hyptiotes holding her web under tension.

Hyptiotes holding web under tension with extra line in bundles near rear and front legs.

Now for trying to shoot video. The capture rate for this little gal in my lawn chair was much too low for me to just set up and wait. I needed to “feed” her prey. So I captured a house fly and anesthetized the fly with CO2 to immobilize it. Then I dropped the fly into the web. I was thrilled when the fly actually “stuck” in the cribellate threads. This stimulated the Hyptiotes, she quickly released the tension in a jerk, then repeated it a couple of times. This collapsed the web on the fly as she moved in for her meal. Remember the spider is really small and positioned in the extreme upper right of the field-of-view at the beginning.

There are a few problems with this video, but it is the best one I’m managed to get so far. The web is very difficult to see through the viewfinder of the camera, so I didn’t aim perfectly so for a moment the spider-and-fly disappear at the bottom edge of the view. Eventually I noticed this and shifted the camera on the tripod to reveal the action.

You may have noticed that the “jerks” as she released the web, early in the video, are very fast. It turns out that Hyptiotes are now famous for their ability to harness the potential energy of the tense web very efficiently. A recent paper by Sarah Han and colleagues, she demonstrated that this spider employs what physicists call power amplification. Here is how they describe the action:

Both spider and web spring forward 2 to 3 cm with a peak acceleration of up to 772.85 m/s2 (Han, et al. 2019)

Other animals that employ elastic-energy storage and recoil usually have anatomical structures, like triggers or catches, associated with this behavior. Hyptiotes manages this feat with pure muscle power. Remarkably they hold the line under tension for hours at a time, waiting for the right moment to release the web and snare dinner.

After the capture, like any good uloborid, Hyptiotes wraps the prey, but does not bite. Members of the family Uloboridae lack venom, they don’t even retain venom glands. So they cannot subdue their prey that way. What they do is wrap the prey tightly in silk, then they engage in external digestion by spitting a mixture of digestive fluids onto the prey ball. This gradually dissolves the prey into a mush that they can suck in. Here is a photo of my resident Hyptiotes with the remains of prey that has been reduced to a wet ball of goo.

photo of Hyptiotes with her meal, the wrapped prey is swathed in digestive fluids. It will eventually be liquified and ingested.

Hyptiotes with her meal, the wrapped prey is swathed in digestive fluids. It will eventually be completely liquified and ingested.

Read more about Hyptiotes power amplification:

S. I. Han, H. C. Astley, D. D. Maksuta, and T. A. Blackledge. 2019. External power amplification drives prey capture in a spider web. PNAS, vol 116 (24) June 11, 2019. www.pnas.org/cgi/doi/10.1073/pnas.1821419116

American Arachnological Society 2021 virtual meeting

Posted on June 12, 2021 by richardbradleyJune 12, 2021

This year the American Arachnological Society (the leading scientific society of arachnid biologists in the Americas) is going to be hosting a virtual annual meeting. The meeting events are from 24 June through 1 July 2021. One consequence of a “virtual” meeting is the cost is dramatically lower. You can register for this meeting for $20, which admits you to all events and programs. If that is more than you can afford, you can request financial assistance. To participate, you need to register by Monday 14 June 2021!

AAS 2021 virtual meeting logo

Check out the full schedule here.

The meeting will feature a number of fun events for arachnid enthusiasts in addition to a full scientific program. These events include:

An Equity, Diversity, and Inclusion Panel Discussion & Workshop
Workshops on Arachnid Collection, Photography, and Identification
Movie nights (Maratus, Sixteen Legs)
Free public talk by Jillian Cowles “THE THIEF IN THE WEB & OTHER STORIES” Jillian is a clinical microbiologist, naturalist, and photographer and the author of the fabulous and lavishly illustrated book Amazing Arachnids (Princeton University Press, 2018).
A virtual bioblitz incorporating the iNaturalist platform
Arachnid phototography and art contests
An arachnid Q&A livestream

The scientific program will feature:

Keynote speaker: Maydianne Andrade, University of Toronto Scarborough “Widows as Windows on Adaptive Plasticity”

Announcement of the Norman Platnick Award

Research Poster Sessions & Student Poster Competition

Daily Plenary speakers: Mercedes Burns, Ivan Magalhães, and Lauren Esposito

Submitted Research Talks (featuring research on arachnids from around the world)

Student Presentation Competition

For more information about this meeting and how to register follow this link.

But there is very little time. Registration closes on Monday 14 June 2021!

The Asterisk Spider; Ocrepeira

Posted on October 29, 2020 by richardbradleyOctober 29, 2020

One of our strangest-looking spiders is Ocrepeira, the asterisk spider. She has an amazing camouflaged color pattern complete with little lumps on her abdomen. She is actually related to our more common orb-weaving spiders, but has a very unusual web.

There are 68 species in the genus Ocrepeira (sometimes known as Wixia). All but three of these are found in the tropics (Central or South America). Of the three northern species, two are known from Ohio. During the Ohio Spider Survey (1994-2014) ten individuals of Ocrepeira ectypa were found, two of Ocrepeira georgia, and four immatures that could not be determined. So this spider isn’t encountered very often. One reason is that they really do an excellent job of hiding, they look just like a broken branch or bud on the stem of a shrub or tree.

Ocrepeira resting on a twig in Adams County, Ohio

Ocrepeira posed front view

Ocrepeira posed side view

This spider is known as the “asterisk spider” because of its web. The web consists of an orb like array of radial threads connected to a loose hub where the spider sits when she is hunting. Because the web does not contain any sticky silk, and because the radial threads spread from the central hub in a star-like pattern, the web is thought to resemble an asterisk mark (_*).

The Asterisk Web of Ocrepeira (photo from Stowe, 1986)

Ocrepeira next to her asterisk web

Ocrepeira at the hub of her asterisk

In his 1976 monograph, Herb Levi describes the natural history of these spiders thus:

“All three species are rarely collected but are found in wasp nests (Levi, 1973). They probably make their unknown orbs in trees and rest at daytime appressed to twigs.”

Now we know that Levi was partly correct, the web is built at night, but it is not a complete orb. The first accurate description of the web of this species was made by Mark Stowe (1978). Mark mentions that it was extremely difficult to observe the construction of the web which is built by the spider very quickly at dusk. When hunting the spider sits at the hub of the web and waits. Prey are detected as they walk on the branches supporting the web, or bumping into one or more of the silk threads. The spider then rushes to the branch and captures the walking prey on the branch. Stowe describes this sequence in his 1978 paper.

“Usually the spider first ties down the prey by rapidly circling the branch and the prey while laying down swathing silk. This prevents the prey from escaping and facilitates subsequent biting. When the venom takes effect, they prey is freed from the branch by biting the restraining threads and after more wrapping the prey is eaten at the capture site or at the hub.”

When Laura Hughes told me about finding a female Ocrepeira she had located in Adams county, we agreed to meet there and observe the spider. We were hoping to see her hunting technique. Thanks to Laura’s great notes and memory we were able to re-locate the spider. When we arrived at the small Eastern Redbud tree at 7:30 pm on 25 September, 2019, she had already built her web.

Ocrepeira in her web in Adams County, Ohio

The weather in early September last year had been very dry, and there were few insects or spiders active in the area. We had hoped to capture some local insects as potential prey and offer them to the spider. Unfortunately, we couldn’t really find suitable prey. Most of the potential prey that we caught refused to walk on the branches. We did get one grasshopper nymph to walk near the spider, but it was evidently too large. The spider did not take the bait. She eventually retreated to the branch and assumed her cryptic posture.

Ocrepeira ignoring a grasshopper (above spider on branch)

So our quest to observe and photograph the hunting technique in the wild was foiled. I captured the spider to see if I could get her to hunt in captivity. I set up a small branch from one of our redbud trees that had about the same sized branches and an arrangement angles similar to the situation were she was captured. To minimize disturbance she was housed in a windowless room at my home. I put a light on a timer coordinated with the light/dark cycle. At night the room was lighted with a dim red light (so I could observe and navigate). Past work with spiders has indicated that many species cannot see red light, and will continue their nocturnal behavior without disturbance. Remarkably, she was quite cooperative and built her asterisk web on her new home.

captive Ocrepeira in her web (flash photo)

I tried several potential prey, including handsome trig (a common bush cricket), moths, small beetles, small crickets, mealworm beetles, and small cockroaches. She did not take the bait. I continued to offer prey each night. The spider built a web every evening then removed it and retreated to a resting position in the morning. All my attempts to get her to feed, failed.

Ocrepeira on branch

I continued the next few nights without success, then on the 2^nd of October, she produced an egg sac. Maybe that is why she wasn’t feeding? I don’t really know. But the very next day I fed her a small walkingstick, and she took it. Everything happened so fast, it was very difficult to see in the dim red light. The spider whipped around the walkingstick in an instant, presumably trailing a silk line to tie it down. Then she moved in and bit near the end of the abdomen.

Ocrepeira bites walkingstick prey (flash photo)

I never saw her use “swathing” silk the way I had expected from Mark Stowe’s description.

After the Ocrepeira began feeding on the walkingstick, I left her in peace. When I checked after the lights were back on in the morning, she was in her typical resting position and there were no remains of the walkingstick.

It was getting late in the season, and I was having difficulty finding prey for the spider. The most abundant insects were large craneflies. They seemed to be good potential prey, and she did take them. Unfortunately it was extremely difficult to photograph captures. Here is one photo of the remains of her cranefly prey, wrapped with silk to the branch near where she hunted. Later in the month she died.

asterisk spider prey; wrapped craneflies

We don’t know how rare Ocrepeira is, there are so few records for Ohio, but it is also a very cryptic spider. It is possible that they are far more common than these records indicate. The records are scattered across the southern half of the state. In Herb Levi’s 1976 monograph there were none from Ohio, the records were scattered along the Atlantic coast from Massachusetts to Florida, with additional records in Georgia, Missouri and Arkansas. Given this paucity of information, it seemed best to return the egg mass laid in captivity back to the location where the female had been found. So Laura returned it to the original site in Adams county.

Ocrepeira egg case in folded redbud leaf

So I’m still hoping to witness an Ocrepeira natural prey capture event, but that will need to wait for another opportunity.

Levi, H.W. 1976. The Orb-weaver General Verrucosa, Acanthepeira, Wagneriana, Acacesia, Wixia, Scoloderus and Alpaida North of Mexico (Araneae: Araneidae). Bulletin of the Museum of Comparative Zoology, 147(8): 378-384.

Stowe, M.K. 1978. Observations of two nocturnal orbweavers that build specialized webs: Scoloderus cordatus and Wixia ectypa (Araneae: Araneidae). J. Arachnol. 6: 141-146.

Stowe, M.K. 1986. Prey Specialization in the Araneidae. pp 101-131 IN Shear, W.A. (editor) Spiders Webs, Behavior, and Evolution. Stanford University Press, Stanford CA.

There is a kleptoparasite in your web!

Posted on August 4, 2019 by richardbradleyAugust 4, 2019

Up against a window and near the edge of our back deck I found a beautiful orb web and one of my favorite spiders in residence. It was a Orchard Orbweaver (Leucauge venusta). She is one of the few green spiders in Ohio, and is also famous for the iridescent silver reflective patches on her abdomen.

An Orchard Orbweaver (Leucauge venusta) in her web

As I leaned over to admire her, I noticed that there was a second spider hanging in among a few strands of slik slung below the orb of the Orchard Spider’s web. I recognized this spider by her distinctive triangular body shape. It was an adult female Neospintharus trigonum (aka Argyrodes trigonum).

I felt like yelling to the Orchard Orbweaver the warning “There is a kleptoparasite in your web!” but she probably wouldn’t have understood. Neospintharus is infamous as a “web invader.” They add a few strands of silk to, or near an occupied spider web. Then they wait until the resident spider captures prey. If the resident is already busy with another prey item, or for some reason doesn’t notice the new potential prey, the Neospintharus sneaks into the web, cuts the prey free, and consumes it herself. This is a mooch behavior given the technical name “kleptoparasitism” based on parasitic theft.

Here are a couple of views of the thief, inches away from the resident.

A Neospintharus trigonum female in a silk tangle below the web of an orchard orbweaver (Leucauge venusta).

In this case crime did pay, because the Neospintharus had evidently captured enough prey to develop and lay a clutch of eggs. Her beautiful inverted-urn shaped egg case was attached to the lower end of her little tangle near the window screen.

An egg case of Neospintharus trigonum

Here is another photo of the distinctive egg case of another Neospintharus trigonum.

photo of egg cases of Neospintharus trigonum

Neospintharus trigonum egg cases

Sometimes Neospintharus isn’t so passive. They occasionally attack the resident spider, eat her, and then take possession of the web. When they do this they eventually replace the original web with a three-dimensional tangle of their own making.

When they are inactive, Neospintharus trigonum can look very un-spiderlike. They fold up their legs agains their body and hang in the web looking more like a triangular bit of leaf or seed pod.

Neospintharus trigonum female

Here is a different female with her egg case.

Neospintharus trigonum with her egg case

In the current case, either the Orchard Orbweaver was too big to attack, or perhaps there was enough prey for both.

Hypsosinga in a web!

Posted on July 6, 2019 by richardbradleyJuly 6, 2019

In early June I had a surprise in our yard. For the first time I found a Hypsosinga rubens in her web. This is a relatively small and rarely-encountered species. The range of the species includes most of the eastern half of North America north of Mexico as well as the prairie provinces of Canada, but few individuals are ever noticed. Almost all the records for the species are obtained in general sweep net samples of fields and field-edges. In his review of this and related genera, Herbert Levi also mentions that some have been obtained from leaf litter samples (Levi, 1971). Nicholas Marcellus Hentz in his iconic monograph “Spiders of the United States” writes in 1875 that “This species is not rare, both sexes having been found on perpendicular webs.” During the Ohio Spider Survey (1994-2014) only four males, five females, and two immatures were collected.

The most remarkable thing about the adult female Hypsosinga rubens that I found on June 6th was that she was in an orb web oriented horizontally. This is very unusual for members of the family Araneidae (orbweavers). Horizontal webs are typical of a different family, the long-jawed orbweavers (Tetragnathidae). In addition to the typical horizontal webs, some members of that family build their webs at an oblique angle, like those of the common orchard orbweaver (Leucauge venusta). Orchard orbweavers are common and familiar, as well as spectacular because of their bright green and iridescent silver coloration. Finding a “typical” orbweaver in a horizontal web was a shock to me. And remember that Hentz states that this species builds a “perpendicular” web. This was my first observation of an undisturbed individual resting in her web.

Hypsosinga rubens female in a horizontal web, viewed from above

Hypsosinga rubens adult female in her web

As you can see from these photos, this is no plain Jane spider! She is bright red-orange and black. Even at her diminutive size (body length about 3/16 inches) the dramatic coloration is striking. Her web was stretched across the upper leaf tips of a gray-headed coneflower (Ratibida pinnata).

I admit to being surprised by how brightly colored some of Ohio’s day-active spiders are! Surely they would be conspicuous to any predator armed with color vision. How they avoid becoming prey is a mystery to me. Here is another photo of her hanging below her web.

Hypsosinga rubens female in her web from below

Because there are several species in the genus Hypsosinga, and each is quite variable in color, I captured this individual and examined her under a microscope. She was an adult female. Here she is in captivity after being anesthetized with CO2.

Hypsosinga rubens female (dark form) in captivity

So you could be excused for wondering, why is Rich writing a blog post about one spider in his yard? The reason is that six days later I found a second individual of the same beautiful species. She was in a proper vertical orb web, suspended among the foliate of an orchid plant on my back deck. And she was a completely different color form!

Hypsosinga rubens female light form in her web

Hypsosinga rubens female (light form) in her vertical web

Here is what she looked like in captivity, you can see that this “light form” has very different coloration. Under the scope her reproductive anatomy was identical to the dark form individual I’d seen a week earlier.

Hypsosinga rubens female (light form) in captivity

Having found my second ever observation of this spider in a natural undisturbed pose would be enough to be exciting. But if you look at the original photo of her in her web you might notice something else unusual, she is oriented with her head (cephalothorax) uppermost! Almost all orb-weaving spiders hang head down. The only other orbweaver species in our area that I’m aware of that habitually hangs in the web head-up is the triangulate orbweaver (Verrucosa arenata).

Triangulate orbweavers are also polymorphic and often very brightly colored. They too have often been found out in the middle of their webs during the day. Are these brightly colored, day-active spiders distasteful? Are they advertising their bad taste with aposematic coloration? As far as I know there is no evidence one way or the other regarding this possibility. Here is a photo of a triangulate orbweaver in her web.

triangulate orbweaver (Verrucosa arenata) hanging in her web, head up.

Not all triangulate orbweavers are as “plain” as this individual. Check out this remarkable color form in a photo taken by Chris Friesen in his yard near Delaware Ohio back in October of 2016.

triangulate orbweaver (Verrucosa arenata), red form, female

If you can avert your gaze from that spectacular spider, notice that she has captured and wrapped a wasp prey item. So she is no slacker at dealing with formidable predatory arthropods!

One other feature of the understudied biology of Hypsosinga rubens is highlighted by Herbert Levi in his review. He speculates that spiders in this genus “make a complete orb probably with a retreat.” Neither of the females in my yard had any sort of retreat associated or near the web. The 12 June female used the “drop and hide” method of reacting to my close approach. It tested my patience to wait until she climbed back up her “safety line” to her web after she dropped. This behavior is typical of orbweavers that do not build a retreat.

As far as I’m aware these are the first descriptions of the webs of Hypsosinga rubens since Hentz’s “perpendicular” comment in 1875. The posture (head up) is very unusual. These casual observations highlight how much we don’t know about our spiders. This species represents the 190th found in our yard, a small (1.3 acre) lot in a primarily agricultural landscape. The remarkable spider diversity here is partly the result of our extensive native plantings, but I’m guessing it is also a reflection of having residents (Amy and I) that are keenly interested in the biota here, and paying attention for the past 28 years.