Re-emerging into the Warm Sunshine

On Monday, I took advantage of very pleasant weather to visit one of our Platte River Prairies I hadn’t seen for a while. The warm sunny day felt great to me, but apparently also invigorated a lot of other creatures. Wild turkeys were in full display mode, with males showing off to each other and to nearby females, and I flushed a prairie chicken from near where it and others had been lekking earlier in the day.

More interestingly, I saw all kinds of insect activity. Big green darner dragonflies were zipping around wetlands adjacent to the river, and nearby patches of bare sand were full of small hordes of brightly colored tiger beetles chasing after flies and other tiny insects.  I wondered whether the adult insects I was seeing had spent the winter as adults, and if so, how.  Green darner dragonflies are migratory, so the ones I saw might have moved back north from wherever they go during the winter.  I’m pretty sure the tiger beetles I saw had spent the winter as adults, sheltered in their burrows.

I’m pretty sure this is the bronze tiger beetle (Cicindela repanda) because it fits both the visual description and the habitat (bare moist sand near the river). This was the most common tiger beetle I saw.
There many fewer festive tiger beetles (Cicindela scutellaria), but they were certainly the most colorful.

As I was crawling through the sand on my belly, trying to get close enough to photograph tiger beetles, I occasionally flushed band-winged grasshoppers that were hanging around on the same patches of bare ground.  I managed to photograph both green and brown ones, which I assumed were different species until I got home and looked more closely at the photographs.  Despite the different colors, the patterns and textures of the grasshoppers looked identical to each other, so I sent the photos to a couple friends who have shown themselves willing to put up with my grasshopper questions in the past.

The brown form of the greenstriped grasshopper was much more common (and harder to see against the mostly still brown grass) in the prairies this week.

Both Ellen Welti and Angela Laws responded and let me know that both the green and brown grasshoppers were greenstriped grasshoppers (Chortophaga viridifasciata).  Greenstriped grasshoppers are band-winged grasshoppers, which are known for their colorful wings and their habitat of crepitation (loud snapping noise) as they are flushed and fly away.  Band-wings also tend to hang out in areas of bare ground, which matches where I found them this week.

The greenstripped grasshopper is very common and abundant in the eastern United States, but it is found in much more scattered populations out here in the west where it tends to be tied to areas of moist soil. The grasshoppers hatch from eggs in mid-summer and then overwinter as late stage nymphs.  Once they emerge in the spring, they molt into their adult form. During the winter they are in diapause (a kind of dormant state) that is apparently broken in the spring, not by temperature, but by increased photoperiod (daylength).  All of this means that greenstriped grasshoppers have to be extremely cold tolerant.  They have to survive the winter, of course, but even after they emerge in the spring they still have to face the kinds of spring cold snaps we’ve been dealing with this year.  During those cold periods, the grasshoppers find a place where they can nestle into some prairie thatch until temperatures rise again.  Then they bask in the sun until they’re warm enough to resume their regular activities.

In its green form, the greenstriped grasshopper is sure handsome, isn’t it?

Ellen shared a great anecdote about how cold tolerant the greenstriped grasshopper can be.  While doing grasshopper research at Konza Prairie (near Manhattan, KS), she put a batch of caught grasshoppers in the freezer – a standard way to kill insects before sorting, identifying, and pinning them.  Three days later, when she brought the bag of frozen insects out to work through them, a greenstriped grasshopper started kicking its legs!  Ellen said she felt bad for the grasshopper and ended up taking it back out to the prairie, where it seemed to be completely unphased by the whole experience and hopped back into the grass.

Seeing how quickly insect activity resumes after cold snaps during the spring is a great reminder of how resilient and well-adapted those creatures are.  We complain about having to put up with wild temperature swings, but we’ve got cozy homes and appropriate clothing to help us cope.  Birds, insects, and other animals don’t have the advantages we have – they’re just tougher than we are.  While not all of them can stand being frozen solid like the greenstriped grasshopper (though many of them can), they have been dealing with crazy weather events for many thousands of years, and will likely continue to do so in the distant future.  I bet they whine a lot less about it too.

Photo of the Week – February 8, 2018

Some aquatic insects can survive being encased in ice – water boatmen, for example, or dragonfly larvae.  But what happens if they are frozen near the surface of a pond and the ice around them melts (or sublimates), leaving them exposed to the air when they thaw out?  This is what I was wondering last weekend, as I poked around the icy wetland at our family prairie.

A frozen dragonfly larva in the wetland of our family prairie.

As I wandered around our wetland, I found several dragonfly larvae and a couple other aquatic insects frozen at or near the surface of the ice.  I’m still trying to puzzle out how they got there.  My best guess is that they must have been swimming near the surface as the water around them neared its freezing point.  Maybe they got cold enough they couldn’t swim back down before the water around them froze?  Regardless, there they were, right at the surface.  In some cases, they were partially exposed to the air as the ice was melting and/or sublimating from around them.

Another dragonfly larva – this one was upside down when it froze.

Dragonfly larvae breathe through gills, which I assume means they can’t survive for long out of water.  They can apparently survive being frozen, at least for a while, but I assume they only survive if they thaw out underwater where they can breathe.  If they thaw out on top of a frozen pond, that seems like a really bad outcome…  If so, the larvae I was seeing were either already dead or doomed to be so.

Gusts of wind were blowing snow across this partially exposed dragonfly larva on the surface of the ice.

I’m still not sure why the larvae would have been swimming near the water’s surface as it froze, or if that’s what actually happened.  It’s not an isolated incident – I find insects near the frozen surface of wetlands and ponds pretty frequently.  Anyone have a great explanation for what’s happening?

Insects After a Hard Freeze

In last week’s Photo of the Week post, I mentioned that I’d spent part of a morning photographing white fluffy seeds in autumn prairie.  (It’s not a bad life, all things considered.)  As I walked that morning, I noticed how quiet it was.  In fact, the only sounds I heard were those of my feet crunching through the dried grass.  We’ve had three below-freezing nights in the last week or so (25, 27, and 28 degrees F), and those cold temperatures have eliminated most insects – and their sounds – from the prairie.

Milkweed seeds in autumn prairie.

However, the prairie was not completely devoid of insects.  As I was photographing seed heads of false boneset (Brickellia eupatorioides), I noticed that one of the flower stems seemed much thicker than it should have been.  Upon closer inspection, it turned out to be a caterpillar.  Anyone know what kind it is?  I certainly don’t.

A caterpillar on a false boneset seed head.

In fact, there were two caterpillars on the same plant.  Did they survive the cold temperatures right there on the plant?  Or did they drop down into the thick leaf litter below during those frigid nights and find enough warmth to avoid freezing?  Are they larvae of a moth that overwinters as a caterpillar?  Or are they the last reproductive gasp of a moth species that migrates north each year in the spring, produces multiple generations, and then finally succumbs to the winter cold?

A second caterpillar on the same plant.

The coloration of the caterpillars matches fall prairie foliage very well, which makes me wonder whether they are of a species that overwinters as a caterpillar – and has protective coloration to match late fall dormant stems.  Maybe one of you will know some of the answers to my questions and can solve the mystery.  That’d be great, but in the meantime, it’s just as much fun to speculate as to know!

The caterpillars weren’t the only insects in the prairie.  Just a few steps away, I found the insect pictured below.  Can you identify it from the front?

Do you recognize the face of this insect?

The photo below gives you a better look.

An assassin bug sits in ambush on the seed head of a dotted gayfeather plant.

The assassin bug appeared to be waiting quietly for another insect to venture near enough to become a meal.  Based on the scarcity of insects in the post-hard-freeze-prairie, that could be a long wait.  Besides the assassin bug and the two caterpillars, the only other insect I saw was a ladybug, though I’m sure there were others that survived the first cold snaps – including wolf spiders.  Long-time blog readers might remember a post from a couple years ago about a wolf spider I found running around on the ice on an 18 degree F day.

So how do insects do it?  They’re cold-blooded, right?  They should be particularly vulnerable to really cold weather…

Well, a good hard freeze does bring death to lots of insects.  However, their species show up again the next year, so they clearly have strategies for getting through the winter.  Many species overwinter as eggs, but others survive as larvae or even adults.  Most of those that overwinter as larvae or adults seek shelter from the worst of the cold by burrowing underground or beneath deep leaf litter.  Even so, they may have to withstand temperatures well below freezing.  Some insects produce a kind of anti-freeze solution to protect themselves from freezing, while others change the way they store liquids within and between their cells so their cells don’t rupture when those liquids freeze and expand.

…and of course there are lots of other strategies.  You can read a technical description of some of those in this research article, if you’re interested.  Or you could read a more general post I wrote last year about winter survival strategies of a number of animals.

What’s happening to the insects in prairies near you?  Have you already seen the big first freeze die off?  Maybe you live in a climate where that never happens?  I’d love to hear your stories.

Photo of the Week – October 21, 2011

Garden spiders, aka black and yellow argiopes, are one of the most recognizable spiders in many prairies (not to mention backyards).  In fact, my kids spent several weeks this August doing daily checks on one big spider in our yard, feeding it every kind of insect they could find.  They had a great time catching insects and figuring out the best way to toss them into the web so that the insect would get tangled up and the spider could rush over and finish it off.

A black and yellow argiope (Argiope aurantia) with its egg sac. Lincoln Creek Prairie - Aurora, Nebraska. (For context, the egg sac was about an inch wide.)

A couple weeks ago, I took the above photo of a black and yellow argiope and its egg sac in a local prairie.  Female argiope spiders typically lay several hundred or more eggs in the early fall, encase them in an egg sac, and die soon after.  (Remember Charlotte’s Web?)  In Nebraska, the eggs hatch in the fall, but the spiderlings remain in the egg sac over the winter before emerging the next spring.  The tough egg sac protects them from winter weather and helps protect the eggs and spiderlings from many predators.

I’ve spent this week at a big conference for scientists of The Nature Conservancy.  One of the themes of our conference has been the need to do a better job of involving people – particularly kids – in conservation.  Clearly, one of the keys to getting kids into conservation is helping them to make personal connections with nature.  I’m convinced that intimate experiences like feeding a spider, holding a turtle, or watching a butterfly emerge from its chrysalis create long-lasting impressions that shape future convictions about the importance of nature.  When my kids are older, I hope that memories of watching and feeding that big spider in our yard will be influential and inspirational to them, regardless of where they go or what they do.  Now if we could just get a big spider in the backyard of every kid in the world…

Black and Yellow Argiopes – the new worldwide ambassador for conservation!