Crab Spider Tent

A crab spider and silk webbing at our family last weekend.

A few of us took a short trip out to our family prairie last weekend.  My daughter was back from college for the weekend and wanted to see what was happening in the prairie, so we did a little canoeing (tight circles in the small pond), hiking, and exploring.  Later, I found myself photographing dotted gayfeather seeds, and while I was looking for more of those plants, I stumbled upon a grass leaf that was bent funny with some kind of white silk holding it in that position.  I had actually walked past the grass leaf before my brain finally registered the fact that I should go back and examine it.

Looking more closely, I could see enough of the creature inside to identify it as a crab spider.  It had been raining quite a bit during the previous couple weeks, so my first thought was that the crab spider had made itself a little rain shelter.  (Crab spiders don’t make webs, but like all spiders, do make silk and use it for various purposes.).  However, my better guess was that it was a nest and that it might contain a bunch of spider eggs.  I photographed it for a few minutes, taking lots of photos, since the breeze was making it hard to keep the spider in focus.

A tiny spiderling, accidentally photographed.

Later, when I was looking through images at home, I was culling all the photos of the spider that weren’t in focus (dang that wind) when I happened to spot something that confirmed my guess.  Right above an unfocused crab spider face, a tiny spiderling appeared – just in one photo, not in any others.  Apparently, this was indeed a crab spider nest, and at least one egg had already hatched.  

The crab spider eventually shifted around and showed its face.

Crab spiders aren’t the only group of spiders that take care of their kids.  Frequent readers of this blog will, of course, remember a previous post of mine showing a mother wolf spider carrying her brood around on her body, and even if you don’t, you may have heard that wolf spiders lug both their egg sacs and newly hatched babies around with them.  Wolf spiders aren’t alone, though, and we’re still learning more about how well various spider species care for their young.  If you’re interested, you can read more in this nice blog post from Biome Ecology.  Otherwise, you can just join me in wishing this particular crab spider’s brood good luck as they disperse and try to find safe places to overwinter.

Hubbard Fellowship Blog – Mysterious Strands of Silk

This post is written and illustrated by Katharine Hogan, one of our Hubbard Fellows.  

In November, I visited the Valentine National Wildlife Refuge on Highway 83 south of the town of Valentine. There had been a burn several weeks previously at the refuge, and I enjoyed a little time wandering around and observing the effects of the fire on the vegetation and exposed sandy soil. In patches, some brave grasses had re-sprouted in defiance of the cooling autumn temperatures. In other areas, the patchy fire had not burned hot enough to do more than singe the thicker sunflower and forb stalks, and everywhere the rodents had wasted no time in churning up the exposed sand, leaving clean, cool piles in stark contrast with the surrounding black ash from the burned vegetation.

I had only been walking around for a few minutes when I came across something that, though strange at first, eventually astonished me in its scope across the landscape. I noticed a patch of flower stalks with some threads of spider silk, strung out from stalk to stalk, not forming an actual web but nonetheless running roughly parallel, using the burned stems as support. Upon further examination, however, I realized that this was not an isolated occurrence within the burn, and that this same patterning of silk strands stretched off in both directions across acres and acres of the burned vegetation.

Although these pictures don’t and can’t really accurately represent the scope of this phenomena, I was able to capture a couple that show, if nothing else, the impressive amount of silk that had been put out for some unknown reason by, one must guess, some very industrious arachnids.

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The lighting makes it somewhat challenging to see, but the density of the webs can be best seen in the upper center of the photograph, and extends outwards from there.  Photo by Katharine Hogan.

My knowledge regarding spiders and their habits is utterly basic. I have a high appreciation for them as fascinating creatures and as ecological players, but my ongoing efforts of understanding have simply not focused on them, focusing instead on plants in part because plants don’t, you know, suddenly relocate on you for inscrutable reasons. At the time, I could only wildly guess as to what caused this phenomenon to occur. Apparently it involved a presumably large number of arachnids deciding more or less in tandem that changing location was a really good idea, but why? And what type of spiders? Were they moving towards or away from something? Was this movement related to the recent fire? What about the decreasing autumn temperatures and daylight?

I did a little digging and came up with a couple potential situations that could describe at least in part what I saw. As always, I would welcome the insights of readers of this post with a better idea of what’s going on! I would love some help in solving this web of mysteries.

This was a typical amount of webbing that had been constructed on each of the thousands of plants across the section of the burn.
This was a typical amount of silk on each of the thousands of plants across the section of the burn.

I found references to spiders of two families that sometimes exhibit tendencies that could explain silk strands such as these. Jumping spiders (family Salticidae) leave “safety lines” of silk behind them as they jump between plants; however, this does not explain the massive amount of silk, nor why it was all aligned in the same direction across the landscape.

The other possible explanation I found was with regards to spiders, not exclusively but predominantly of the genus Erigone, that, according to a 2005 article in the Bulletin of Entomological Research, will sometimes display what is called “mass ballooning”, where large numbers of spiders in tandem migrate short distances across landscapes, leaving behind “spectacular amounts of silk on the ground” (J.R. Bell et al.). The reasons for this behavior are still largely not understood, but hypothesized explanations have included sudden changes in temperature, humidity, and other factors largely dependent upon the microclimate of the population in question.

Several other studies during the 70s and 80s also supplied some evidence that the propensity of spider populations to balloon was correlated with the “predictability” or stability of their habitats. In the case of Greenstone (1982), populations that selected for habitats subject to more frequent change, e.g. open spaces near water sources, were more likely to balloon than species that favored prairie habitats. If habitat changes are positively correlated with the likelihood of a spider population ballooning, could this suggest the recent prescribed burn as a causal factor in the event whose aftermath I witnessed at the wildlife refuge?

I honestly don’t have a clue. Other interests and appreciations aside, I am very much a “plant person” and feel uncomfortable coming to any conclusions regarding a group of organisms about which I know so fabulously little. I do know, however, that the scope of the phenomena I witnessed was truly impressive, and thus I gained a little more appreciation and awareness of the unseen lives of the tiny critters around us. As always, input on the matter would be much appreciated. If any of you readers have any insights on the matter, please let us all know in the comments! Thanks!

 

Sources cited:

Bohan, David A., et al. (2005) Ballooning dispersal using silk: World fauna, phylogenies, genetics and models. Bulletin of Entomological Research 95, 69-114.

Greenstone, M.H. (1982) Ballooning frequency and habitat predictability in two wolf spider species (Lycosidae: Pardosa). Florida Entomologist 65, 83–89.

 

 

Photo of the Week – December 4, 2015

We had a winter storm pass through our area at the tail end of the Thanksgiving weekend.  After a light coating of ice, we got a couple inches of fluffy snow.  Monday was a gloomy overcast day – too dark to inspire me to venture out with my camera.  However, Tuesday morning began with a beautiful sunrise and calm winds.  A fantastic opportunity for winter prairie photography.   Unfortunately, I had to enjoy the light from the interstate as I drove to a meeting.  Wednesday was another great sunrise and morning of light, but I was on the road again – heading to a different meeting.  Yesterday, most of the snow melted and, just like that, the first snow of the year was gone.  Not a single photograph taken…

So, instead of posting a beautiful photo of fluffy snow on the prairie today, I’m reaching back to a photo from August.

Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.  Click on the image to see a larger version – and maybe the hidden visitor on it.

I like this photo of a stiff sunflower for several reasons, including the interesting shapes of the ray flowers (“petals”) that are not yet fully extended.  However, I also like the photo because there is a hidden visitor on the flower that I didn’t see until well after I took the photo.  Can you see it?

Here is a cropped version of the image to give you a better look.

Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
Can you see the tiny larva feeding on pollen?

I don’t know what this little larva will grow into, but it appears to be feeding on pollen and stringing lines of silk between anthers as it moves.  I featured a similar larva in an earlier post that showed a sunflower which had been “sewed shut” by silk – probably as a protective measure to allow the larva to feed on the flower under cover.  I wonder if this larva will follow the same procedure as it gets bigger and can’t hide as easily out in the open.

Interestingly, the photos from that earlier post featuring the “seamstress larva” were taken on the same day as the photo in this post.  In fact, I took the photo of the tiny larva just a few minutes after photographing the sewed-up flower.  You’d think I’d have been on the lookout for larvae on sunflowers, but I still missed it, even through my macro lens.  Then, I missed it again as I worked up the photo later, even as I was looking closely at it on the computer to adjust sharpness, etc.  I guess that’s a testament to the effectiveness of the hiding strategy of this little larva!

I hope its camouflage allowed the little larva to grow up, pupate, and have lots of offspring to carry on its strategy.  I bet it did.

Photo of the Week – September 10, 2015

A few weeks ago, I took my camera across town for a walk in a small local prairie.  There were numerous flowers blooming, but the stiff sunflowers (Helianthus pauciflorus) were stealing the show.  I shot quite a few photos of them from various angles.

Hover fly on Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
This little hover fly was enjoying a meal of stiff sunflower pollen.  Lincoln Creek Prairie, Aurora, Nebraska.

Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
The sunflower perspective.

I noticed that a few sunflowers seemed to have their “petals” (technically speaking, they are the ray flowers) folded in toward the center of the flower.  I’d seen this quite a few times before, but this time I decided to investigate.  I gently pulled the petals apart and found they’d be held down with what appeared to be silk.  Beneath them, an insect larva was hiding and, presumably, feeding on pollen or other flower parts.

Caterpillar in Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
A closed-up stiff sunflower.

Caterpillar in Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
The larva revealed.  Note the remnants of silk and the anthers still sticking to the petal after I pulled everything apart.

Caterpillar in Stiff sunflower (Helianthus pauciflorus) Lincoln Creek Prairie, Aurora, Nebraska.
A close up of the caterpillar (?)

I’m not expert enough with insect larva identification to know for sure, but I’m guessing the larva is a moth larva – I know at least some of those have the ability to make silk.  Some of you reading this will surely know more about them and comment below.  (Thanks for your help.)

A few days later, I ran across some similarly closed up flowers in a different prairie.  When I opened those up, there was another larva inside, but it was much darker in color.  I wonder how many different species have this behavior?

The larva I found was just one of many examples of insects that create safe hiding places for their young to feed in.  Spittle bugs and gall-forming insects are two others that are common in prairies.  Of course, for every great hiding strategy, there is at least one predator that has developed a counter strategy.  I don’t know what eats the petal-tying larvae, but I bet there’s something out there.  I’m pretty sure guys-with-cameras are not the only ones who can find them.  Fortunately, for the larva I found, I wasn’t hungry at the time.

 

“Should I Stay or Should I Go?”

It’s good to be back in the prairies after spending last week in the mountains.  The mountains were beautiful and daytime temperatures were pleasantly cool, but I sure enjoyed the chance to catch up with the goings on in our prairies yesterday.  As if to welcome me home, the weather provided about an hour of bright overcast skies and light winds around lunchtime – perfect weather for a little close-up photography.

As I wandered, I found a crab spider perched atop an upright prairie coneflower (Ratibida columnifera) flower.  I’m a sucker for crab spiders, so I crept up and snapped a photograph of it.

Crab spider on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
Crab spider on upright prairie coneflower. The Nature Conservancy’s Platte River Prairies, Nebraska.

I was surprised the spider was sitting so high on the flower – it seemed awfully visible to predators, and poorly placed to capture pollinators coming to visit the blooming portion of the flower below.  Just as I was wondering what it was up to, the spider answered my question for me.  It popped itself up on its “tiptoes” and let loose a long silk trail.

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If you look closely, you can see a long silk thread emerging from the abdomen of the spider.

The spider was attempting a technique commonly called “ballooning”, though “kiting” seems a more appropriate term.  Small spiders use ballooning to travel long distances by releasing long silk threads into the breeze and floating off to wherever the wind carries them  Often, the spider only goes a short distance, but it’s still a faster mode of transportation than walking on short little legs!  Sometimes, if the wind is right, a ballooning spider can go many miles.

In this case, the light winds were apparently insufficient to carry the spider off, and after it failed to launch, it detached its silk thread and sat back down (dejectedly?).  I imagined the spider’s disappointment at having steeled itself for a potentially long trip only to find that it wasn’t going anywhere after all.

Oh well...
Oh well…

As I walked off, I left the spider with good wishes that it would catch a better breeze in the near future, but also with a silent warning.  It’s great to go to new and different places, but sometimes travel just helps you appreciate how nice it is to be home.

Testing Assumptions – The Milkweed Seed Fiasco

A few months ago, I mentioned a technique that we use to clean milkweed seeds after harvest.  We spread the fluffy seeds out on a concrete floor and light the thin pile on fire, burning the fluff off the seeds.  It’s quick, easy, and fun.  I learned of the technique from a fellow prairie restoration ecologist many years ago, and we’ve been using it ever since.  I’ve also shared the idea with quite a few others.

Burning the fluff off of milkweed seeds. Don't try this at home.

Those of you who have either read this blog frequently or know me personally know that I am a strong advocate for experimenting with techniques whenever possible.  In fact, I often reduce people to blank stares by blathering on about the importance of always testing restoration and other methods to be sure we’re using the most effective strategies.  Surely, then, over the last decade or so that I’ve been using and advocating the “burn the fluff off” technique, I’ve followed my own advice and checked to make sure it actually works, right?   Well…

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