Photo of the Week – October 19, 2018

Dotted gayfeather (Liatris punctata) seeds at our family prairie last weekend.

This is the season of flying fluffy seeds.  Asters, thistles, blazing stars, milkweeds, and other late season flowers are sending their seeds into the air, a few of which might actually land in a place where they can germinate.  Each of those seeds is attached to a filamentous structure, variously called a pappus or coma, depending upon the species of plant.  Those fluffy structures catch the wind and allow the seed to travel many miles, in some cases – though most land within a few meters of their origin.

Seeds that can float on the air are a nice adaptation for plants, but they are also attractive photographic subjects.  Over the last week, I’ve photographed the seeds of common milkweed (Asclepias syriaca), dotted gayfeather (Liatris punctata) and tall thistle (Cirsium altissimum) in some local prairies.  Here are a few of those photos for your Friday enjoyment.

Common milkweed seeds lined up inside their pod, nearly ready for launch.
A common milkweed seed temporarily hung up on big bluestem.
The coma of this milkweed seed got stuck and was drifting lazily in the breeze, having become separated from its seed.
Tall thistle seeds.  Many of these get eaten by insects before they get a chance to fly away, but at least one of these managed to escape – so far.
Dotted gayfeather seeds, backlit by the autumn sun.

Killer Thistles

Two years ago, I posted some photos of ants and other insects that had died on the sticky lower portion of thistle flowers.  At the time, I speculated about whether or not the sticky bracts below the thistle blossoms were an adaptation to prevent ants from reaching the flowers and “stealing” nectar.  Since ants aren’t fuzzy and don’t dependably go from flower to flower like bees do, they probably don’t provide many (any?) benefits to the flower in return for the nectar they take.

Dead ant stuck to bottom of wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
Dead ant stuck to bottom of wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.

After that post, a friend sent me a journal article detailing a study (see citation below) in the 1980’s that looked at this same phenomenon, trying to figure out what benefit the thistle might get from having sticky bracts.  They used Liquid Paper to coat the bracts and make them non-sticky and then measured seed predation between coated and non-coated plants.  Overall, their results were fairly inconclusive, though they did see higher seed predation by insects on non-coated flowers in one of their sites.  The mystery remains!

One interesting part of the study was that of the 331 insects they found trapped on the bracts of Flodman’s thistle at Frenchman’s Bluff in Minnesota, 96% were ants.  (Given that result, I’m not sure why they focused on seed predation – I don’t think ants feed much on thistle seeds?)  I have been trying to keep track of what insect species I see stuck to thistle bracts during the last few years, and while ants do make up the majority of dead insects found there, a number of other species show up as well.

Dead ant stuck to bottom of wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
The ant on the left appears to have completely lost his head over sticky thistles.

All the photos on this page were taken on the same morning last month.  I was walking around our family prairie and looking at the wavy-leaf and Flodman’s thistles (Cirsium undulatum and C. flodmanii) to see what was feeding on them, as well as what insects had become fatally stuck.  As usual, the majority of dead insects were ants, but there were several bees and even a little cicada as well.  More interesting, I also tried to pay attention to insects that seemed to move across the sticky flower bracts without getting stuck.  Crab spiders and stink bugs were two that seemed to have no trouble.  Spiders, at least some of them, have a special coating on their fuzzy feet that help keep them from sticking to their own webs – does that help them not stick to thistle bracts?  Maybe?  What about stink bugs?

Dead bee on bottom of wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
This bee probably chose a nice sheltered place to spend the night without knowing it’d be the last choice it ever made.

Dead bee on bottom of wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
This bee had been stuck for a while.

Dead beetle on wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
This tiny beetle was another victim of the killer thistles.

Sphinx moth on wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
Sphinx moths and many other pollinators feed on the tops of on wavy-leaf thistle flower. It’s the underside that’s dangerous.  If you look closely at the bottom of the thistle flower, you can see a couple wings…

Dead cicada on bottom of wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
…and those wings belong to this poor dead cicada.

Stink bug on wavy-leaf thistle flower. Helzer family prairie near Stockham, Nebraska.
Stink bugs and crab spiders are among the insects that are apparently unaffected by the sticky thistle bracts.  This stink bug was moving around the flower with no apparent problems.

These are the kinds of mysteries that make walking through prairies fun.  Maybe someday we’ll figure out the secret of thistles’ “bracteal exudate”, but in the meantime, it’s just one of many prairie interactions we can marvel at.

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Journal Citation:

Bracteal Exudates in Two Cirsium Species as Possible Deterrents to Insect Consumers of SeedsAuthor(s): Mary F. Willson, Pamela K. Anderson and P. A. ThomasSource: American Midland Naturalist, Vol. 110, No. 1 (Jul., 1983), pp. 212-214Published

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Photo of the Week – January 29, 2015

Ok, I admit it – I’m a sucker for crab spiders.

A crab spider on Flodman's thistle (Cirsium flodmanii) at the Helzer family prairie.
A crab spider on Flodman’s thistle (Cirsium flodmanii) at the Helzer family prairie.  July 2014.

As much as I enjoy looking at prairie flowers, I enjoy them even more when there’s a crab spider lying in wait among their petals.  I must have more than a hundred photos of crab spiders on flowers, but when the lighting is good and I see those long hairy legs and cute little face… I just can’t help myself!

Do you suppose I need some kind of intervention?

“Hi, my name is Chris Helzer and I really like crab spiders.”  (Hi Chris…)

“It’s been three weeks since I last photographed a crab spider…”  (Applause)

Photo of the Week – December 26, 2014

The sun finally reappeared this week after what seemed like a month of absence.  I figured the best way to celebrate the end of dreariness was a couple of prairie hikes. I started by wandering along a creek at our Platte River Prairies to see what the resident beaver family had been up to.  Green sunfish slipped in and out of hiding places in the deep pools behind beaver dams, but little else was moving in the water.  Later, the sound of frantic chirping turned my head in time to watch a sharp-shinned hawk just miss its prey.  I couldn’t tell what kind of bird the hawk was chasing because it didn’t stop flying until it was out of sight.  I also caught a quick glimpse of a small mouse scooting through the thatch, spotted a perched eagle in a far off tree and flushed a small flock of mallards from an backwater wetland.  Not a bad way to spend an afternoon!

Later in the day, I stopped at our family prairie and roamed around until the sun went down.  As the sun dropped, its warm light illuminated the golden brown prairie and I managed to take a few photographs – something I’ve not done much of lately.  Here are a few of those photos.

A stiff goldenrod seed is stuck in the velcro-like hairs on the stem of a plant of the same species.  Helzer family prairie, Stockham, Nebraska.
A stiff goldenrod seed is stuck in the velcro-like hairs on the stem of a plant of the same species. Helzer family prairie, Stockham, Nebraska.

A Flodman's thistle (native species) stands out against the sky.
A Flodman’s thistle (native species) stands out against the sky.

The spiny beauty of Flodman's thistle seed heads.
The spiny beauty of Flodman’s thistle seed heads.

Tall dropseed (Sporobolus compositus) in golden prairie.
Tall dropseed (Sporobolus compositus) in golden light.

Stiff goldenrod
A stand of stiff goldenrod and mixed-grass prairie.

Happy Holidays, and best wishes for your New Year!

Isn’t it a little late to be nesting?

As you might remember, my Photo of the Week last week was an image of a fledgling meadowlark I’d found in mid-September.  At the time, I’d talked about how surprised I was to see such a young bird so late in the season.  Well, last Friday, Eliza Perry, one of our Hubbard Fellows, called me to say she’d just found a nest full of tiny birds – did I want to come take a look?  Of course I did.

American goldfinch chicks sit in a nest about three feet off the ground in a tall thistle (Cirsium altissimum) plant.  Platte River Prairies, Nebraska.
American goldfinch chicks sit in a nest about three feet off the ground in a tall thistle (Cirsium altissimum) plant. Platte River Prairies, Nebraska.

I’m pretty sure what Eliza found was an American goldfinch nest.  The bills and markings on the birds look right, and we spotted an adult goldfinch nearby.  However, the best supporting evidence was that the nest was located in a thistle plant (a native thistle species, by the way) and had thistle down in the nest cup.  There is a strong tie between American goldfinches and thistles.  Unlike most other bird species which feed their young on insects, goldfinches instead feed them regurgitated seeds – especially those of thistle plants.  In fact, they often delay their nesting until those thistle seeds have ripened.  Here is a link to photographer/naturalist Stan Tekiela’s post on this topic, if you’re interested in learning more about the topic.

These birds are even further behind the meadowlark in their development, and it’s already getting pretty cold overnight, so the nestlings’ chances for survival might seem slim.  Of course, the difference between the meadowlark and the goldfinches is that the goldfinches have adults around to help them.  Both have a challenging fall and winter ahead of them, but nothing others of their species haven’t dealt with countless times before, I guess.

A better view of the nest placement within the tall thistle plant.
A better view of the nest placement within the tall thistle plant.

Thanks to Anne Stine, our other Hubbard Fellow, who graciously helped hold equipment for me as we photographed the nest.  Because of the very bright early afternoon sun, I had Anne hold a diffuser near the nest to reduce the harshness of the sunlight while I held a small flash unit to better illuminate the birds.  We worked quickly and got out of the way so the parents could resume their feeding duties.