Well-Nigh Wordless Wednesday: Sampling Sabino Canyon Post-Fire

You probably all know that there have been several very large fires in Arizona this summer.  Ever wonder what a mountain stream looks like after a forest fire?  Here’s an example from Sabino Canyon in Tucson, AZ after the Aspen Fire a few years back:

Sabino storm

Sabino Canyon after the Aspen Fire. Photo by Dave Walker.

Notice how the water is black?  It was full of ash from the fire that had been washed downstream during the monsoons.  The water even smelled like a campfire!  And what I’m doing in this photo, sampling in the stream downstream of a major burn area as a monsoon storm rolls in – that’s dangerous and you shouldn’t do it.  Made for an awfully pretty photo though!

(Just so there’s no confusion, I’m collecting bugs in that photo, NOT spearing fish.  Everyone seems to think I’m spearing fish when they see this…)


Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

From the Literature: Oxygen, Temperature, and Giant Insects

I hope everyone liked the giant insects post last week!  It was one of my favorites to write.  The topic is just so fun!  I continue with the subject this week by describing a scientific paper that was released in July.  It combines several things I love (giant insects, aquatic insects, and respiration)  into one manuscript of pure science fabulousness!  Let’s get to it, shall we?

You probably learned as a kid that insects are ectothermic (aka, cold-blooded).  Ectothermic organisms are largely unable to regulate their body temperatures, so their bodies remain close to the temperature of their environments.  As the temperature increases, processes like metabolic rates speed up.  The opposite happens at cold temperatures and everything slows way down.  Ectotherms survive best under a range of temperatures where their body processes work efficiently, but the animal is still able to get everything it needs (food, water, oxygen, etc) from the environment.  They’re like Goldilocks: they don’t like things too hot or too cold and prefer for things to be just right.

Oxygen plays a big role in the interaction of ectotherms with their environments, especially at extreme temperatures.  Let’s consider a hypothetical insect, say a grasshopper.  As the grasshopper gets warmer, its metabolic rate increases and its body processes become more efficient.  However, as the grasshopper’s metabolic rate increases, so does its oxygen consumption.  At some point, the oxygen demand of the grasshopper may become greater than its oxygen availability and all sorts of bad things start to happen as its body processes start to break down.  Oxygen plays a role at very cold temperatures as well, leading scientists to propose that oxygen can set thermal limits (the maximum and minimum temperatures our grasshopper can survive) in ectotherms.

One problem though: terrestrial insects don’t fit the pattern observed in many other ectothermic animals.  This may be because their respiratory systems do not depend on lungs and blood to deliver oxygen to their cells and instead deliver oxygen directly to their cells via a series of tubes that connect to the outer environment.  This creates a terribly efficient system that provides enough oxygen even at high temperatures for many terrestrial insects.  Quite simply, their respiratory system provides enough oxygen even under the worst conditions.  But what if the insects live in oxygen-limited environments, such as water?  Might oxygen play a role in setting those upper thermal limits then?


Image from http://www.glommaguiden.com/foto_2003/ bilder/030416_dinocras_cephalotes.htm.

Researchers Wilco Verberk and David Bilton considered this question and determined that if the thermal limits of any insects were to be limited by oxygen levels, aquatic insects were the most likely suspects.  So, they chose an insect that requires a low temperature and flowing water as their subject, the stonefly Dinocras cephalotes.  If the maximum temperature the stonefly could tolerate was limited by oxygen consumption, the maximum tolerable temperature would decrease in low oxygen water while it would increase in high oxygen water.  They then developed a simple experiment to determine whether this was the case.

The team placed stoneflies in flow-through chambers in a water tank and ran 10°C water containing various mixtures of oxygen and nitrogen (20% O2/80% N2 = normal, 5% O2 /95% N2 = low oxygen treatment, and 60% O2/40% N2 = high oxygen treatment) through them.  After letting the stoneflies acclimate for an hour, they ramped the temperature of the water up 0.25 degrees per minute until the critical temperature was reached, i.e., the stoneflies started showing signs of thermal stress such as lack of movement and leg twitching.  Then they compared the critical temperatures for each treatment to determine if their hypothesis was correct.

And it was!  They discovered that the upper thermal limit increased almost 3°C in the high oxygen water compared to water containing normal levels of oxygen.  Conversely, the upper thermal limit decreased in low oxygen water by about 1.5°C compared to that at normal oxygen levels.  The conclusion: oxygen levels can set upper thermal limits in larval aquatic insects!

Now you might be wondering why this is exciting or what any of this has to do with giant insects.  The results are interesting for several reasons, but largely because they show that some insects do experience oxygen-induced changes in their upper thermal limits.  This means that, while terrestrial insects might be able to obtain enough oxygen at any temperature to meet their needs, aquatic insects and other insects that live in oxygen limited environments can reach a temperature at which their oxygen demand outstrips the oxygen available to them.  Consider how an insect such as a stonefly gets the oxygen it uses.  They don’t have any spiracles (the pores through which terrestrial insects “breathe”), so oxygen is simply absorbed through the exoskeleton.  Many stoneflies have gills to make this process more efficient (the bigger your body surface, the more oxygen you can absorb from the water), but it’s still a very slow process.  The size of these insects may be limited as a result.  Aquatic insects that rely on absorbing oxygen from the water rather than going to the surface to breathe are also unable to regulate their oxygen uptake very well.  They can do various behaviors to increase the flow of oxygen into their bodies when they become oxygen stressed, but oxygen becomes toxic at very high concentrations.  Aquatic insects can’t do much to prevent oxygen from flowing into their bodies, so this can be a problem.

And this brings us to the giant insect part of the paper.  Verberk and Bilton propose that oxygen limitation at temperature extremes may have contributed to the rise of insect gigantism in the late Carboniferous and early Permian.  This makes sense considering how many of the giant insects were insects that probably had aquatic nymphs (proto-dragonflies, mayflies, and stoneflies, among other aquatic organisms).  The high levels of oxygen at the end of the Palaeozoic meant that oxygen could be absorbed more efficiently by aquatic insects and allowed them to become larger.  I covered this hypothesis last week, so check that post for more details.

Alternatively, Verberk and Bilton suggest that oxygen toxicity may have played a significant role in promoting insect gigantism.  How can an aquatic insect cope with increasing levels of oxygen in water and prevent oxygen poisoning?  They can get bigger!  If insects increased in size as oxygen levels in water rose, then they could counteract the negative effects of high oxygen levels on their bodies.  Oxygen levels at the end of the Palaeozoic were so high that aquatic insects likely had to become very large to prevent oxygen poisoning.  Giant immatures then led to giant adults.  Hence, giant insects that resulted from the limits of their respiratory systems in very high oxygen environments!  It’s a very interesting, new idea.  I suspect many people will do further tests in the future to determine whether this might really have been possible, so we’ll see if it holds up to further study.

I love this hypothesis!  Still, I have to point out that there is one major assumption that the entire hypothesis is built upon, that the giant proto-dragonflies, mayflies, stoneflies, etc had aquatic nymphs.  Modern dragonflies, mayflies, and stoneflies have aquatic immatures, so it’s likely that their predecessors did too.  However, there is no fossil evidence of aquatic nymphs for these groups at the time of the giant insects.  For all we know, the griffenflies and giant mayflies may have had terrestrial nymphs, which would make Verberk and Bilton’s hypothesis fall apart completely.  While the authors did acknowledge this assumption, I think their position would be strengthened if a fossil of even one aquatic immature could be found from that time period.  Without that piece of evidence, I fear this hypothesis is built upon a shaky foundation, one that might not hold up to scrutiny.

But wow!  A new explanation for how giant insects may have evolved!  And focused on the aquatic stages of insects!  You can see why I’m excited by it.  I can’t wait to see the research generated by this paper in the future.  It’s going to make for some very interesting reading!


Literature Cited:

Verberk WC, & Bilton DT (2011). Can oxygen set thermal limits in an insect and drive gigantism? PloS one, 6 (7) PMID: 21818347

This paper is open access!  Full text available online here:  http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0022610


Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

Swarm Sunday – 8/21/11 – 8/27/2011

dragonfly swarm banner

The dragonfly population of the Midwestern US seems to be exploding!  The last few weeks have seen a lot of swarming activity, and this week is no exception.  Swarms occurred in the following locations over the past week:


Tupper Lake, NY
Rowlett, TX
Poplarville, MS
East Tawas, MI
Hartford, AZ
Surprise, AZ
Hamilton, MO
Leawood, KS
Garden City, MO
Omaha, NE
Kansas City, MO
Pocatello, ID
Saint Joseph, MO
between Columbia and Harrisburg, MO
Nortonville, KS
Falmouth, MA
Edwardsville,  KS
Delton, MI
Mundelein, IL
Atlantic Beach, NC
Creston, IA
Park Rapids, MN
Palm Coast, FL
Marco Island, FL
Beaver Bay, MN
Fennville, MI
Mount Ayr, IA
Belton, MO
Tiffin, IA
Midland, TX
Great Falls, MT
Bowling Green, OH
Wheatfield, IL
Captiva Island, FL
Marshfield, MA
Shreveport, LA
Winnetka, IL
Strafford, MO
Gambier, OH
Mt. Vernon,  IA
Sturgeon Bay, WI
Bourbonnais, IL
Connersville, IN
Pueblo, CO
Franklin, IN
Onamia, MN
Plainfield, NJ
Brooklyn, NY
Decorah, IA
Miami Beach, FL (2 swarms)
Concord, NH (2 swarms)
Bloomfield Township, MI
Juno Beach, FL
Stafford Springs, CT
Watseka, IL
Jamaica Plain, MA
Chicago, IL
Walsenburg, CO
Between Bradley and St. Anne, IL
Marblehead, OH
rural Glenville, MN
Lebanon,  OH
Franklin, IN
Roscoe, IL
Hollywood Beach, FL
Ellis, KS


Trenton, ON
Calgary, AL

Whew!  Long list!  But very exciting for someone like me who’s trying to collect as much data as possible on these swarms.  Thanks to the 300+ participant so far this year.  You all make this research possible!


Have you seen a dragonfly swarm? I am tracking swarms so I can learn more about this interesting behavior.  If you see one, I’d love to hear from you!  Please visit my Report a Dragonfly Swarm page to fill out the official report form.  It only takes a few minutes! Thanks!


Want more information? Visit my dragonfly swarm information page for my entire collection of posts about dragonfly swarms!


Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

Friday 5: Aquatic Insects, In Print!

You all know how much I love aquatic insects.  If you’ve been following my Friday 5 posts then you also know how much I love books.  It thus seems only proper that I do a Friday 5 about non-dragonfly aquatic insect books!  If you want to learn about and/or identify the aquatic insects in your area, I recommend one of my 5 favorite aquatic insect books.  In no particular order, they are:

Voshell bookA Guide to Common Freshwater Invertebrates of North America by J. Reese Voshell Jr.

This is a nice little field guide type book that covers a broad range of aquatic insects and their relatives throughout the U.S.  The book is VERY general, so you’ll only be able to identify any invertebrates you see in the water down to family at best.  The book is also more expensive than I feel it should be.  Still, it provides a great overview of aquatic insects.  If you’re a beginner, or just want to look at some really nice aquatic insect drawings, this is a great book to have in your collection!  Personally, I most often use it to show people generalized pictures of aquatic insects when I teach or do outreach events.  You know, when someone asks something like, “This one time I saw this little brown bug looking thing swimming in the water.  What was it?”  Invaluable for that sort of thing!

Speaking of great aquatic insect drawings:

Aquatic Entomology by W. Patrick McCafferty

This book has the best aquatic insects drawings I’ve ever seen.  It’s a little old at this point (the version currently available is a reprint of the original 1981 version), but the drawings – oh, the drawings!  They make having this rather out-of-date book entirely worth owning!  The book also contains something very special: visual keys.  They’re in standard dichotomous key format (you start at the top with two choices, choose the one that best fits your specimen, rinse and repeat until you’re delivered to a name for your bug), but there are pictures imbedded within the couplets so you have a lovely picture to go along with nearly every option.  They are unbelievably easy to use! A few of the families included in the keys have undergone name changes since the book was released, but it’s still an incredible resource.  If you’ve never identified insects with a key, these are a fantastic way to get started!  And did I mention the drawings?  :)

Now, if you REALLY want to identify an aquatic insect in North America, this is THE book to use:

An Introduction to the Aquatic Insects of North America by R. W. Merritt, K. W. Cummins, and M. O. Berg

Ah, Merritt and Cummins (and now Berg).  What would aquatic entomologists do without you?  This is a monster of a reference book and contains well-illustrated dichotomous keys for the orders, families, AND genera of nearly every aquatic insect in North America.  1200+ spiral bound pages of aquatic insect goodness!  It’s not perfect and there are things that I would like to see improved, but every aquatic entomologist should have a copy.  I’ve got 3!  I use it at least once a week too.  If you’re not an aquatic entomologist but are serious about identifying aquatic insects, this is the book to get.  The keys are good, the reference section is amazing, and there are several chapters of general information at the beginning that are really excellent.  Plus, it comes with a great CD-based visual key to the orders to get you started.  This is probably the book I’ve spent the most time with of any book I own – and I’ve read Harry Potter and the Prisoner of Azkaban and Good Omens more times than I can count!

Biological Atlas of Aquatic Insects by W. Wichard, W. Arens, and G. Eisenbeis

This book is essentially a catalog of scanning electron microscope images of the biologically important structures of many aquatic insects.  Ever wonder what a mayfly gill looks like up close?  Or what the area between the two halves of the whirligig beetle eye looks like?  This is the ultimate book for answering any burning questions of this sort you might have!  It’s not cheap (about $90 on Amazon), but it’s an amazing resource and well worth considering if you have the means to do so.  I’ve looked through it a hundred times and I  discover something new every time!  Love it.

And finally…

Caddisflies: The Underwater Architects by Glen B. Wiggins

I considered putting 5 general aquatic insects on this list, but I just can’t pass this one up!  Caddisflies are amazing, and this book WILL make you appreciate their beauty and amazing diversity.  Like Merritt, Cummins, and Berg, this probably isn’t the sort of book you buy unless you’re an aquatic entomologist, but that’s a shame.  It’s amazing!  It includes keys (admittedly, a little outdated) to family and genus, detailed distribution information, and fantastic illustrations.  Each genus get a page of text and a page of images, including the whole larva, their case/net (where applicable), and several structures of importance in identification.  But the book is so darned pretty that it’s fun to just flip through the pages and marvel at how wonderful nature really is.  Caddisflies are so cool!  And this book will make you fall in love with them.

There are so many books in the world that these are just a handful of the total books available about aquatic insects.  I’ve got lots more, but I really love these!  Most of the books I’ve featured today are more academic than my usual Friday 5 book lists, but I think they all have something to offer to non-entomologists too: pretty pictures, information that non-entomologists might actually care about, and assistance identifying the aquatic insects in your area.  Might want to try before you buy these books as they tend to be a little spendy, but they’re all excellent books and worth a look.  Check ’em out!


Unless otherwise stated, all text, images, and video are copyright ©TheDragonflyWoman.com

Well-Nigh Wordless Wednesday: Bark Scorpion Eating

One of my favorite experiences when I TAed insect systematics last fall was the non-insect arthropods lab.  We fed many different large, scary scorpions, centipedes, and spiders during the session and it was a lot of fun.  This was one of them:

bark scorpion eating cricket

Bark scorpion eating a cricket

Though quite small compared to other scorpions in Arizona, the bark scorpions are pretty formidable because they’re highly venomous, plus they can climb walls.  Really fun to watch eating though!  (If you haven’t ever seen a scorpion eating, I’ve got a video of it.)


Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

A long, long time ago, in a galaxy.. well, right here

I grew up loving minerals and geology.  My dad was a rather obsessive mineral collector when I was a kid and is still as passionate about the subject as I am about entomology.  He never really bothered with fossils though, so it wasn’t until grad school that I became interested in them.  My advisor adores insect fossils and even worked at an amazing fossil insect deposit in Germany, so I heard all sorts of fascinating stories.  When he offered a fossil insect class, I jumped at the chance to take it.  (What’s not to love about combining my interest in minerals with my interest in insects?!)  It quickly became my favorite grad-level class and I formed a deep and lasting appreciation for insect fossils during the class.

For the next two Monday posts, I’m going to share some of the insect fossil love! Today I’m going to cover the giant insects of the Carboniferous and Permian (358-289 and 290-248 million years ago respectively) and my favorite theory suggesting how these giant insects were able to develop.  Next week I’ll discuss a recent paper.  Let’s jump right into the giant insects, shall we?

Goliath beetle

Goliath beetle. Image from Wikipedia.

There are arguments over which living insect species is actually the largest insect on the planet.  Most of the debate centers around one problem: how do you define “largest?”  If you go by weight, the heaviest adult insect on record is the giant weta in New Zealand.  It’s thought that some of the African Goliath beetles might actually be heavier, but fewer of them have been weighed.  The heaviest immature insect on record is a Goliath beetle, so they’re definitely up there near the top.  If we go by length, the longest insect is (not surprisingly) a stick insect from Borneo.  There’s often a biggest species identified for each insect order too.  For example, the largest true bug is a giant water bug from South America that tops out at nearly 5 inches long.  All of these insects are big, the giants of the living insects.  However, they all pale in comparison to the largest insects ever discovered on Earth!


Griffenfly. Image from Wikipedia.

The largest insect was a member of the Meganisoptera, an extinct order of insects called the griffenflies or “giant dragonflies.”  As you can see, griffenflies superficially resemble dragonflies and have similar wing and body shapes, so they are commonly confused with the Odonata.  If you’ve ever heard that the largest insect ever was a dragonfly, this is why, but it’s not quite correct.  They were not true dragonflies, rather the precursors to the modern dragonflies.  And they were BIG!  REALLY BIG!  The largest insect ever discovered was a griffenfly called Meganeuropsis permiana, a giant with a wingspan of nearly 28 inches (71 cm) and a body length of almost 17 inches (43 cm).  Can you imagine an insect with a two foot wingspan buzzing around your head?!  Still, as amazing as the griffenfly fossils are, there’s still very little known about them.  Most fossils contain only wings fragments with no body attached.  The immatures remain unknown.  No one has any idea what these things ate, but given their relationship and similar appearance to the dragonflies, it is assumed they hunted flying animals just like their modern odonate relatives do.  Ultimately, as cool as fossils are, they leave you longing for more information.  The griffenflies have been extinct for well over 200 million years, so we might never learn much about them.


Paleodictyoptera. Image from http://www.geocities.co.jp/NatureLand/5218/ pareodhikuthioputera.JPG

The griffenflies were the biggest insects ever, but they weren’t the only big insects around during their time.  Giant mayflies and an extinct group called the Paleodictyoptera (at right) were also roaming the planet at the time.  Some enormous  scorpions and myriapods (like centipedes and millipedes) were also present, as were giant amphibians.  (How cool would it be to see a giant proto-frog eating a giant proto-dragonfly?)  That’s not to say all arthropods were giant during the late Carboniferous.  Most were similar in size to the insects we see today, with a few amazing exceptions that absolutely dwarfed their relatives.   But why did they get so big?  And why are none of these truly giant insects alive today?

insect respiratory system

Diagram of a simple insect tracheal system.

Because I work with insect respiration, my favorite theory of how insect gigantism came about has to do with how insects breathe.  If you recall from my post on insect respiration, insects depend on tubes called tracheae and tracheoles to exchange gasses with the environment.  The system works because there is less oxygen within the insect than outside the insect, so oxygen tends to flow down the tubes in an attempt to create an equilibrium.  It’s thought that insect size is limited by this system and that insects like the Goliath beetle and the giant weta are about as big as modern insects can be and still get all the oxygen they need.  So how was it possible for a 17 inch long griffenfly able to survive if the biggest insects today are as big as they can get?

Happily, there is evidence that oxygen levels on Earth have changed dramatically over time.  In fact, life on our planet began when there was very little or no oxygen on the planet.  By the late Carboniferous, 280 million years ago, there was so much oxygen on Earth that it made up about 35% of the gasses in the atmosphere.  This high level of oxygen could have in turn led to increased flow of oxygen into the insect respiratory system, at least compared to what we see at our current oxygen level of 21%.  Increased flow of oxygen into the tracheal system meant that the size limits the respiratory system imposed on insects also increased and insects were able to get bigger.

And it looks like they did!  The biggest of the giant insects happened to be flying around about the same time the planet’s oxygen levels were the highest they’ve ever been, suggesting that respiration played a role.  The giant insects then disappeared during the Permian, right about the time the oxygen levels dropped to a low 15%.  And when the oxygen levels rose again during the mid-Jurassic?  You guessed it!  Giant insects popped back up for a while, only to disappear when the oxygen levels dropped to the modern 21%.

This is only a theory of course and it’s unlikely we’ll ever know for sure whether this was really how it all worked, but the hypothesis certainly fits the fossil and climatological data well.  It has also been well received by entomologists, so the hypothesis is likely to hold its own for some time.  Several researchers have even pursued experiments in an attempt to support the validity of the high oxygen – giant insect correlation and gotten some interesting results.  Next week, I’ll discuss one such recent paper that deals with an oxygen study performed on stonefly nymphs.  It makes some interesting points regarding ancient insect gigantism, so I hope you’ll check back!



Grimaldi, D and Engel, MS.  2005.  Evolution of the Insects.  Cambridge University Press, 755 pp.

Graham, JB, Dudley, R, Aguilar, NM, and Gans, C.  1995.  Implications of the late Palaeozoic oxygen pulse for physiology and evolution.  Nature 375: 117-120.

Dudley, R.  1998.  Atmospheric oxygen, giant Paleozoic insects and the evolution o aerial locomotor performance.  Journal of Experimental Biology 201: 1043-1050.


Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

Swarm Sunday – 8/14/11 – 8/20/2011

dragonfly swarm banner

Another great week of dragonfly swarm reporting!  This past week saw the rise of the “bugnado,” swirling swarms of midges, in various parts of the Midwestern US along the Missouri River.  According to some reports, these bugnadoes are attracting dragonflies that then form swarms themselves.  It’s like an enormous all-you-can-eat buffet for the dragonflies!  However, it sounds like some people in the areas where these bugnadoes are forming are less than thrilled about the arrival of huge numbers of dragonflies, even if they are ridding them of unwanted bugnadoes.  For example, check out the brief report on MyWeatherTech.com.  “To make matters worse?”  Sigh…  I can only wish I were lucky enough to see one of these bugnado-induced dragonfly swarms!

Swarms occurred in the following locations over the past week:


Boca Raton, FL
Marathon, FL (2 swarms)
Rogers, AR
San Francisco, CA
Dubuque, IA
Georgetown, TX
Paris, TX
Plymouth, NH
Onsted, MI
Cottonwood, MN
Los Lunas, NM
New Lenox, IL
Uvalde, TX
Granger, IA
Brooklyn, CT
Peoria, IL
Porter Corners, NY
Shawano, WI
Monkton, VT
North Oxford, MA
Box Springs, GA
Liberty Township, OH
Bourbonnais, IL
Prairie City, IA
Key West, FL
Douglas, MA
Rowlett, TX
DeSoto, IA
Columbia, MO
Bloomington, IL
Breckenridge, MO
Bozeman, MT
Van Meter, IA
Ida Grove, IA
Lake City, IA
Temple, TX
Durham, ME
Box Springs, GA
Salem, NH
Scott Air Force Base, IL
Cambria,  WI
Hastings, IA
St. Joseph, MO
Gower, MO
Silver City, IA
Okay, OK
Cambria, WI


Thunder Bay, ON

Before I end this post, I’d like to direct everyone to a post that Jim Johnson at Northwest Dragonflier posted this week about the variegated meadowhawk migration in the Pacific Northwest.  He’s got a list of ways you can help scientists (including me!) understand the variegated meadowhawk migration and contribute to a greater understanding of migratory and swarming behaviors.  Citizen Science for the win!    Also, Harlan Ratcliff at The Roused Bear demonstrates how difficult it is to photograph a dragonfly swarm.  Check it out!


Have you seen a dragonfly swarm? I am tracking swarms so I can learn more about this interesting behavior.  If you see one, I’d love to hear from you!  Please visit my Report a Dragonfly Swarm page to fill out the official report form.  It only takes a few minutes! Thanks!


Want more information? Visit my dragonfly swarm information page for my entire collection of posts about dragonfly swarms!


Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com