Aquatic Microhabitats

Hello everyone!  It’s my first real blog post in a while, so I hope it proves to be worth the wait.  I feel that it’s time to talk about a subject that I find fascinating: microhabitats in aquatic environments!

A stream might look like a fairly monotonous environment, with water traveling inexorably downstream.  However, if you really take the time to look, you’ll notice that there are lots of little pockets of space in a body of water that have slightly different sets of conditions compared to the little pockets of space around them.  These are microhabitats, small areas that have a particular set of conditions unique to that area, and insects are incredibly good at exploiting them.

Take, for example, the stream in this photo:

Prairie Ridge stream

Prairie Ridge stream

That’s the stream at Prairie Ridge Ecostation, where I work.  I think it’s a fascinating stream largely because it has very few insects in it, much lower diversity than one might expect for a reasonably clean stream in this part of the world.  I’ve got a group of high schoolers who are investigating the reasons why there are so few insects in the stream, but the few insects we find are found only in very specific places.  I draw your attention to the location I’ve indicated with the arrow:

Deep pool

Deep pool

That is a pool, an area of deeper water with lower flow.  Pools like that tend to have a lower oxygen concentration than adjacent areas of the stream because the water is deep (remember that oxygen moves very slowly in water and the deeper the water, the longer it takes for oxygen to reach the bottom) and comparatively still (lower flow often = lower oxygen).  In that particular area of the stream you would normally find swimmers, things like the predaceous diving beetles and backswimmers, things that like deep, calm water so they don’t have to fight the current to swim when they go to the surface to breathe.  Curiously, that is one group of insects that is conspicuously missing from this stream and I’m trying to figure out why.  But that’s a subject for another time!  Let’s contrast that deep pool with this area right here:

Stream rooty pool

At first glance, it might look like those two areas are very similar, and in some ways they are.  You’ll find relatively low flow and low oxygen levels in both areas, but the area indicated here is deeper, has a small sandbar that protects a little pocket of water behind it, and contains a lot of roots and other substrates on the steep bank that are absent in the adjacent pool.  This area is well out-of-the-way of the main flow, so swimming insects that rely on surface oxygen could easily live in this spot if this stream had them (e.g., it would be a good place to find whirligig beetles or those diving beetle, if we could find them anywhere in the stream).  However, you do find one thing clinging to the roots on the banks: jewelwing damselfly nymphs from the family Calopterygidae.  You find lots of them there!  Damselflies rely on oxygen dissolved in the water to breathe, have gills, and are rather inefficient swimmers.  The flow is so low in this area that they are at a low risk of being washed downstream if they become dislodged, but the oxygen levels are also rather low.  Thankfully, the roots give the damselflies something to hold onto if they need to move closer to the surface to get more oxygen, and you will almost always find them clinging to those roots.

This stream is so shallow and the flow is so low that the riffles, the areas where rocks and other objects introduce turbulence into the system, are pretty wimpy and the turbulence they generate is mild.  However, this little riffle is where you find most of the caddisflies in this section of the stream:

riffle

Riffle

They are mostly caddisflies in the family Glossosomatidae and you’ll find them clinging to the underside of rocks where they build cases out of rocks.  Like the damselflies, the caddisfly larvae have gills and rely on dissolved oxygen to breathe.  Riffle areas are often the areas of highest oxygen in a stream because the rocks break up the flow and stir up the water, bringing oxygen rich water to the bottom of the stream far more quickly than oxygen could move there on its own.  However, there’s a trade-off: living in the area of highest oxygen often means that you’re out in the strongest flow in the stream.  Insects that live in this part of the stream typically sport a variety of adaptations that help them stay in place.  In the case of the caddisflies in this stream, they have both a set of hooks at the end of their abdomens and build themselves little harnesses of silk and rocks that keep them pressed firmly against the surface of the rock.  They might be right out in the middle with water constantly slamming into them as it flows downstream, but if you’ve ever had a chance to try to pry one of these insects off a rock you know that they are really well attached.  They’re not going anywhere!

Moving just a few inches downstream can mean a big change in the local conditions.  Take this log, for example:

log in stream

Log in stream

On the upstream side, there’s a small pool where the flow is relatively slow, the water is a little deeper, and the oxygen is a little low.  Just on the other side of the log is an area of turbulence and higher flow.  There’s a more oxygen there, but also more flow.  On the upstream side of the log you’d expect to find swimmers (except not in this stream) and downstream you’d expect to find the kinds of things that cling to rocks.  They are literally five inches apart, but the habitat is completely different!  Another foot downstream  is the start of a very deep pool that contains a lot of fish, but virtually no insects.  Considering the number of these microhabitats that are present in this one little stream (and I have only shown you 10 feet of the total length of the stream), you can see how aquatic insect diversity might go up as the stream becomes more complex and contains a greater variety of microhabitats.

When I go collecting with people who haven’t ever done it before, they typically comment on how I find all sorts of different things when they are finding the same thing over and over again.  It’s not that I’m better at catching things, that my technique is better, because it’s not.  It’s because I know that the odd little pool under the undercut bank has different insects than the rocks out in the middle of the stream and both have different insects than those lurking in the leaves that the pooled area downstream.  It takes a little practice, but with time anyone will start to see the huge variety of microhabitats.  It’s just a matter of looking, of not assuming you’ve collected everything in a stream or a pond because you’ve collected in one place.  Nature is far too clever and complex for that!  Keep looking and poke around in the places you might not expect to find things.  You might be very glad you did!

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth

The Purpose of Caddisfly Case Extensions: A Case Study

Well, Science Sunday ended up getting pushed to Monday, but that’s okay.  It happens!  But today I’m going to share a fascinatingly simple study with you about caddisflies, so I hope it was worth the wait.

I haven’t talked about caddisflies all that much on my blog yet, but I really should.  They are incredibly interesting little insects and hugely diverse as far as aquatic insects go.  Caddisflies fly around on land as adults and look like little bland moths:

caddisflies

Caddisfly adults

Their order name, Trichoptera, means hairy wings, and if you look closely at the wings you’ll understand why: rather than scales, as you see in their close relatives the butterflies and moths, caddisfly wings are covered in hair.  Their common name, caddisfly, is based on a peculiar structure that the aquatic larvae and pupae use, the case.  Not all caddisflies build cases, but those that do build them using silk that they produce and materials they gather from the stream such as algae, pebbles/sand, leaf bits, pine needles, small pieces of wood, etc.  There are a huge variety of cases, many of which are species specific so that you can identify the species based solely on the case.  Others are less distinct, but regardless of the structure of the case, they tend to be big, bulky, heavy things that are much larger than the larvae carrying them.

Over the years, researchers have proposed a variety of purposes for caddisfly cases.  Some are likely helping the caddisfly breathe by stirring the water around the larva, allowing it to collect oxygen from the water via gills that run along the abdomen.  Cases may protect some species from predation as fish and other aquatic predators are less likely to eat something that looks like a pile of rocks or leaves than a soft, squishy insect.  Still other caddisflies may use their cases to weigh them down, causing them to sink to the bottom so that they can move about fast flowing streams with less risk of being swept downstream.  Each species may use its case for a slightly different purpose, or even more than one.

One species of caddisfly, Dicosmoecus  gilvipes, builds a case from silk and plant bits, adding small pebbles as they get older.  The first through fourth instars also attach needles from Douglas fir to their cases (the fifth and last instar does not), attaching them near the top of the case so that they stick far out to either side:

Dicosmoecus gilvipes

Dicosmoecus gilvipes larva. Redrawn from Limm and Power 2011.

This is a rather peculiar arrangement of materials, so researchers Michael Limm and Mary Power wanted to figure out why those fir needle wings were so important.  They considered two hypotheses.  First, the wings might protect the larvae from predation.  Even if the little rocks didn’t discourage fish from eating the larvae, perhaps the pointy spikes sticking off the sides would.  Alternatively, the extensions could help stabilize the larva so that the larva would be less likely to tip over in areas of high flow in a stream.

To test these hypotheses, they did two simple experiments.  In the first, they released caddisfly larvae at the site where a stream flowed into a deep pooled area containing steelhead trout.  One person hid behind a boulder and released the larvae, which were swept into the pool.  A second person observed the fish and counted how many times each larva was approached by the fish, were “mouthed” by the fish, or eaten.  They did three treatments: caddisflies with the case intact, caddisflies with the douglas fir needles clipped off, and naked caddisflies that had been removed from the case prior to release.  In the second experiment, the researchers constructed a large rocking water tank that would roll the larvae over.  They placed a larva on the bottom of the tank and turned the machine on, then counted how many times each larvae rolled before it recovered its footing and how long this took.  They then compared the number of rolls and the time to recovery between caddisflies with cases intact and with the fir needles clipped off.  The team also measured the cases to determine how the width, length, mass, and center of mass changed with the addition of the fir needles.

The reseachers learned that the fir needles increased the width of the case by 410%, the length by 36%, and the weight by 24% and shifted the center of mass upward off the streambed.  They also learned that, while the steelhead readily consumed naked caddisflies, there was no difference in the number of approaches or the number of times the caddisflies were mouthed between the larvae with the extensions and those without.  Clearly the case alone was sufficient to prevent predation regardless of whether the extensions were present or not.

The results of the rocking tank were interesting though.  Larvae with the fir needle extensions rolled three times less than larvae without the extensions.  They also regained their footing more than three times faster with the extensions than without.  The cases might be providing other benefits to the larvae, but Limm and Power concluded that the function of the fir needles is to stabilize the larvae in areas of high flow.  Apparently it’s worth the extra effort of finding the fir needles and carrying around a much more unwieldy case if it means that you are more stable in the stream.

So, why does this matter?  According to calculations the authors did, the drag force required to tip a larva over is more than four times greater when the larva has the extensions than when it does not.  This means that the larvae can safely walk out into areas of the stream with flow up to two times faster without getting tipped over and washed downstream.  The extensions also help the larvae orient themselves so that they’re positioned parallel to the flow.  This decreases the chance of being swept away.  All of these benefits combined likely allow the larvae to wander out into areas of the stream where they would not otherwise be able to go.  Food limits the number of Dicosmoecus  gilvipes that can live in any particular stream, so by increasing their stability by the simple addition of a few Douglas fir needles, the larvae increase the area where they can forage for food in the stream, allowing more individuals to survive in any given area.  Pretty darned cool!

This is yet another example of how an insect can make a very simple, small change that provides huge benefits – just another example of why insects are such amazing creatures!

Literature Cited:

Limm, M., & Power, M. (2011). The caddisfly Dicosmoecus gilvipes: making a case for a functional role Journal of the North American Benthological Society, 30 (2), 485-492 DOI: 10.1899/10-028.1

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

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…)

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

Friday 5: My Favorites Places to Collect Aquatic Insects in Arizona

I shall begin today’s Friday 5 with a quick true story.  Imagine a girl of 21 who loves insects and is applying to grad school.  She knows she wants to be an entomologist, but she hasn’t narrowed down her area of focus.  All she knows is she loves dragonflies, those gorgeous aquatic insects that flit happily around streams, wetlands, and ponds.  She applies to schools and then has to choose which one to go to.  She eventually chooses Arizona, where she will work with an aquatic entomologist.  She tells her family members the good news: she’s moving to Arizona to work on dragonflies!  Hooray!  Now imagine the look of dismay on the face of each relative when she tells them.  That look is followed by what quickly becomes the dreaded question: “You’re going to Arizona to study AQUATIC insects?!”

So, yeah.  My family generally thought I’d lost it when I told them I was packing up and moving to Arizona for grad school.  Never mind that a good number of them had been to Arizona several times themselves and know that there’s a decent amount of water here.  I myself remember trips to the local spring-fed oasis and several streams in the mountains when I lived here as a young child and came back to visit my grandparents.  I knew there was water here and I wasn’t going to let any of those naysayers get me down.  I was going to study aquatic insects in the desert, gosh darn it!

Since I started grad school, I’ve had the opportunity to visit many, many aquatic habitats in Arizona.  Some of them, like the area where I do my summer field work, are appallingly disgusting.  Others are gorgeous and pristine.  Today I’m going to share my top 5 places to collect aquatic insects in Arizona.  Some are favorite locations due to the insects they contain and others because the area itself is so amazing, but they’re all special to me.

Arivaipa Creek

Arivaipa Creek

Arivaipa Creek. I just wrote about this creek, so I won’t say much more here.  This creek is one of my favorites because getting to go there is something special in and of itself.  The area is also incredibly beautiful and is home to some fantastic insects.  Really love this creek!  Check out the post linked above if you would like more information about the area or my recent trip there.

Madera Canyon

Madera Canyon

Madera Canyon.  I’ve been going to this canyon stream all my life.  In fact, some of the very first photos I ever took were at Madera!  Madera Canyon is in the Santa Rita Mountains south of Tucson and east of Green Valley, AZ.  The creek flows mostly over the big rocks you see in the photo, and for the most part it flows year round.  (Yes, I count that little 4 inch wide trickle you sometimes get in the summer as “flow!”).  Madera is very pretty, but I also love the insects I find there: lots of caddisflies, sunburst beetles, two types of whirligig beetles, water scorpions, fly larvae, lots of other beetles and bugs.  The creek is even home to a unique beetle (an riffle beetle)  that is thought to be found only in this one creek!  The downside is the canyon is VERY popular for birding (there are some rarely spotted birds there), so there are usually a lot of people there.

Reynolds Creek

Reynolds Creek

Reynolds Creek. I recently wrote about aquatic insects with suction cups and described my joy at discovering net-winged midge larvae for the first time.  I found them in this creek.  Reynolds Creek is in the mountains south of Young, AZ and north of Globe.  It’s way out in the middle of nowhere, so it’s usually visited only by campers and hikers.  The pine forest surrounding the creek is stunning and the water is cold and clear, so it is an entirely pleasant place to spend a few hours or the night.  There are all kinds of interesting things in this creek too.  However, the sheer elation I experience every time I find the blepharacerid fly larvae here would be enough to keep me coming back, even if there was nothing else to find.

Salt River

Salt River

Salt River (a few miles upstream of Roosevelt Lake).  The Salt River is one of the few big, perennial rivers in Arizona.  As such, it is heavily utilized by people who enjoy water sports (tubing and rafting are both very popular – the location in the photo is a raft pullout point) and is therefore far from pristine.  However, this is still one of my favorite places to collect.  The water flows swiftly and powerfully, and it gets quite deep in places.  This means that there are some excellent flow-adapted insects in the river.  My favorite: the gigantic hellgrammites this river produces!  They’re close to 3 inches long and they’re fierce.  In fact, I tell my aquatic entomology students to put them into their own bags when they collect them from this river.  The hellgrammites will eat everything else in the bag before they expire, leaving you with a single bloated hellgrammite floating amongst an assortment of insect legs.  This river is also one of the only places I’ve found sisyrid larvae, but I’ll discuss them further in a future post.

Three Forks

Three Forks

Three Forks. Three Forks is located in the White Mountains east of Alpine, AZ at the confluence of the East Fork of the Black River, Coyote Creek, and Boneyard Creek.  The photo doesn’t do this location justice at all as the bright sun at the high elevation consistently causes me problems when photographing this area.  Three Forks is a high elevation, cold, fast flowing stream, so it’s got some great insects in it.  My favorites are the water pennies, the flat mayflies (heptageniids), and the aquatic moth larvae.  You can only collect in specific areas of Three Forks though.  It has become a conservation site for an endangered snail that is being decimated by invasive crayfish, so you now need special permission to access the protected area.

So those are my top 5 areas in Arizona for collecting aquatic insects!  If you ever visit Arizona, any of these places are well worth visiting even if you have no interest in collecting.  I think they are some of the most beautiful areas of Arizona.

I wish everyone a happy New Year!

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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com

Friday 5: Aquatic Insects that Suck

For today’s Friday 5, I’m going to discuss five aquatic insects that suck.  No, not that kind of sucking!  These are insects that have suction cups, or suction cup-like structures, that allow them to live in their aquatic habitats.  Now I don’t know about you, but I find it pretty amazing that there are insects with suction cups on their bodies, so I feel the need to share the love!  In no particular order, I present 5 aquatic insects that suck:

water penny

Water penny, top view

water penny

Water penny, bottom view

1. Water pennies.

Water pennies are funky insects – and yes, that IS an insect!  As adult beetles, most species aren’t that exciting, just nondescript black beetles.  But the larvae, pictured here, are bizarre!  These insects don’t have suction cups on their bodies like most of the other insects on my list today.  Instead, their whole broad, domed shaped bodies work like suction cups!  I’ve written about how water penny larvae work before, so I won’t go over it in detail again here.  However, if you think of the little plastic suction cups you use to stick things onto windows, you’ll have a pretty good idea of how the suction works.  You’ll find these living on the tops of rocks in cold, fast flowing streams.

Blepharicerid larva, top

Net-winged midge larvae, top

Net-winged midge larvae, top

Net-winged midge larvae, bottom. The dark, round discs are the suction cups.

2. Net-winged midges.

Ah, blepharicerids.  I can remember the first moment I found one of these in a stream.  I nearly yelled out in utter joy!  It’s one thing to see pictures in a book and quite another to find hundreds of them all over rocks in a stream.  These fly larvae are truly amazing.  They’re bizarrely shaped, even by insect standards, with constrictions along the length of the body.  Each constricted section also contains a suction cup.  Like the water pennies, they live right out on top of rocks in cold, fast flowing streams, so they’re constantly being slammed with water as it flows downstream.  The suction cups keep them from being swept away!  (If you think the larvae of these flies are interesting to look at, I highly recommend that you take a look at the pupae.  Weird!)

predaceous diving beetle

Predaceous diving beetle (Thermonectus nigrofasciatus)

dytiscid foot

Predaceous diving beetle foreleg. The suction pad is made up of several individual suction cups.

3. Predaceous diving beetles.

These are the only adult insects I know of that have suction cups.  And, they don’t use their suction cups to prevent their washing downstream like most aquatic insects with suction cups.  Any idea what they might be used for?  Hint: only the males have them.  These suction cups are used during mating!  Predaceous diving beetles are extremely well adapted for swimming and exhibit very smooth, domed bodies that allow them to move through the water with surprising grace.  If you’ve ever tried to pick one up with forceps, you know how slippery these little buggers are!  This causes problems when a slippery dome-shaped male wants to climb onto his slippery domed-shape mate’s back and get down to business.  So, they evolved suction cups on their forelegs!  You can see them there in the photo – lots of little suction cups making up a big suction pad.  The male presses the suction pad onto the female’s back and is able to hold on long enough to mate.  Pretty neat, eh?

Rhithrogena impersonata

Rhithrogena impersonata. Photo from http://www.troutnut.com/specimen/482.

Rhithrogena impersonata

Rhithrogena impersonata, bottom. Photo from http://www.troutnut.com/specimen/482.

4. March brown mayflies.

Mayflies in the genus Rhithrogena (family: Heptageniidae)  are rather similar to the water pennies in that they do not have true suction cups.  Instead, they have flat bodies and their abdomens are ringed by broad, flat gills.  The space between the gills works like a suction cup and keeps these mayflies attached to the rocks on which they live in streams.  While these nymphs are not dome shaped like the water penny larvae, their suction cup works in a similar manner.

Leech

Leech. Leech sucker is inset.

5. Leeches.

Leeches are not insects.  In fact, they’re not even arthropods!  However, they are aquatic and they definitely have suction cups, so I’m including them in my list.  Leeches use their suction cups to grab the substrate or to hold onto their prey as they suck their fluids.  I also personally think they add to the overall distasteful appearance of these animals.  I mean, what’s not to love about an animal that uses a sucker at one end to attach to you and a sucker at the other end to suck your blood?  :) (Okay, I’ll admit that I do actually like leeches.  Ever seen one swim?  It’s both horrifying and mesmerizing and I can’t tear my eyes away!)

Don’t know what I’ll do next week!  I have a long list of ideas, so it will depend on my mood when I sit down to write.  Maybe something Christmasy!

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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com

Collecting Insects: A Net for Collecting Aquatic Insects

It’s been too long since I last posted a tutorial for my Insect Collections series, so today I’m going to share my best secret for collecting aquatic insects.  A lot of people overlook aquatic insects when they work on their collections.  It’s a shame really – there are some fantastic insects in water if you take a few minutes to look!  I think part of the problem is that most people think you need to have fancy nets that cost $60+ or other special, expensive equipment to collect in water.  This couldn’t be further from the truth!  Today I’m going to show you how to make and use a reasonably sized, easy-to-carry aquatic net for collecting insects in water, one that my advisor recommended to me when I started grad school.  Are you ready for this complicated design?  Breathe in through your nose and out through your mouth to prepare your mind for the complicated steps this tutorial is going to involve.  Ready?  Then gather the things you need:

Essential Equipment

soup strainer

Essential equipment

  • one sturdy all metal kitchen strainer, preferably stainless steel.  (A solid frame around the basket is essential, so make sure that part isn’t going to collapse or separate from the handle if you put a little pressure on it.)

Whew!  Are you tired yet?  And if you want to be REALLY fancy, then you’ll want these things as well:

Optional Equipment

strainer extras

Optional equipment

  • metal rod, stick, dowel, etc (my metal rod came from Bioquip and cost around $8, but anything long and roundish that’s reasonably comfy to hold will do.  Avoid things that might give you splinters!)
  • duct tape (any project worth its salt involves duct tape, so you know this is gonna be good!) or waterproof tape

Okay, you’ve gathered your equipment.  Now let’s put the net together (here comes the complicated step):

 

soup strainer

Completed net. (Note: the duct tape on the handle is there to identify this as my strainer when I'm out with my students on field trips. It has no other function.)

Congratulations!  You now have a really great little net for catching aquatic insects!

I’ll admit that people scoff at my soup strainers and I get laughed at when I strap several of them onto my fishing vest.  Granted, I do look like some sort of deranged Kitchen Rambo stomping around in streams and ponds.  However, regardless of how dorky you look as you strain a pond or stream, soup strainers make fantastic aquatic insect nets!  For one thing, they’re cheap.  Look for sales and you can frequently get all metal strainers for less than $10 at stores like Target, Wal-Mart, and Ross.  Cheap is good.  If one breaks, simply chuck it in the recycling bin and start using a new one.  If you lose it, who cares?  The metal mesh also doesn’t get ripped the way aquatic nets do, so they’re super durable.  Soup strainers are lightweight, so you can carry several with ease.  I have a carabiner hooked onto my fishing vest that I loop through a couple of strainers when I’m out in the field.  And, they’re easy to use.  Trust me – it’s hard to beat a soup strainer for collecting aquatic insects.  I have a fancy aquatic D-net and I hardly ever use it.  Instead, I use my soup strainers.

There are 2 downsides to using soup strainers though.  One is that the mesh size is large, so sometimes it is best to use the more expensive “official” aquatic insect net, especially if it is important to know the number or diversity of insects you pull out of the water.  The other downside to soup strainers is that they’re short, so you have to get your hands wet to use them.  That’s not so bad if you live in AZ and the water rarely gets down below 40 degrees.  I lived in Colorado for a long time though, so I know there are places and times of the year when you really don’t want to stick your hands in the water.  That’s where the optional equipment comes in!  Here comes another complicated step.  Cut off a 12-15  inch long piece of duct tape and tape the handle of your strainer to your longish, roundish, pole-like object:

strainer with extension

Strainer with extension

Tada!  Now you’ve got yourself a nice long handle that keeps you well away from the water and allows you to collect in deeper water without getting wet.  You’ll need to replace the tape occasionally, but you’ll get a lot of use out of your MacGyver’ed soup strainer before you do.  If you spring for a more expensive roll of waterproof tape, it will last a lot longer.

Using your strainer is easy!  In a stream, hold your strainer in the water so that it is downstream of the area you wish to sample.  Stir the substrate up, either with your other hand, your foot, or with the front edge of the strainer.  Let the loose material flow into the strainer bowl, pull the strainer out of the water, quickly sift through the material in your net, and pluck the insects out!  (I recommend using feather forceps for handling aquatics as a lot of them are very soft-bodied and you don’t want to crush them.)  Dump whatever’s left back in the stream.  You’ll use a similar substrate-stirring technique in ponds, but you’ll have to sweep the net through the stuff you stir up because there’s no flow.  If you get a bunch of muck in your strainer, simply hold your strainer at the surface, half in the water and half above the water, and swish it gently back and forth.  The silt and other small debris will flow out of the strainer and leave the bigger things behind.

I know, I know.  It sounds completely stupid.  But it works!  I’ve handed soup strainers to well over 100 people in the last few years and I’ve won a lot of converts.  It’s amazing what you can collect with them.  Considering the price, the ease of transport, and the ease of use, you can’t go wrong.  I use mine all the time!

Me collecting in Florida Canyon

Me collecting in Florida Canyon with my trusty soup strainer!

Happy collecting!

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Print, save, or e mail this tutorial in PDF format!  Click on this link and the PDF will appear in a new tab or window.

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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com

Flat mayflies!

There are all kinds of flat insects in fast flowing streams.  In the White Mountains of Arizona, you can find a few types of flat mayflies alongside the water pennies on the same submerged rocks.  Take a look at these photos:

heptageniid

Flat headed mayfly, bottom view

heptageniid

Flat headed mayfly, bottom view

This mayfly belongs to the flat headed mayfly group and is REALLY flat!  Bug legs tend to curl up when they’re preserved, like in this specimen, so this mayfly would actually be much flatter than it appears here if it were alive.   Flat headed mayflies have several adaptations to flow that you can see in the images above.  First, take a look at the gills, the plate-like structures sticking off the sides of the back half of the bug.  They stick out from the side of the body rather than up like they do in many mayflies.  This helps them keep their gills close to the surface of the rock and inside the boundary layer .  Second, when these insects are alive, they keep their legs held far away from their bodies and absolutely flat against the rock.  These bugs have enormously long legs, but they are also very flat, so they are able to fit them within the boundary layer too.  Finally, they have big, broad, flat heads.  They keep these pushed against the rock, within the boundary layer as well.  The whole bug is only a few millimeters thick, even though they can be close to an inch long!  These are probably some of the flattest bugs there are.  It is a great adaptation to living in a high flow aquatic habitat.

Flat headed mayflies move in a strange way.  Unlike the water pennies, which keep their legs tucked under their bodies and walk along the rock much like other insects do, flat headed mayflies hold their legs flat against the rock and far away from their body.   This makes it hard to walk.  In fact, they tend to shuffle along the rock rather than walking.  Imagine wandering across the floor on all fours.  This is how most insects walk, with their bodies held far away from the surface they’re walking on.  It’s quick and efficient.  Now imagine lying flat on your belly with your legs behind you and your arms out to your side, then crawling commando-style with your body only an inch above the ground.  It’s a lot harder to do, right?  Flat headed mayflies don’t move very quickly or very gracefully.  However, if they pick their bodies up off the rock, they risk getting caught in the current and being swept downstream.  So, they keep their legs close to the rock and push themselves across the rock by pushing with the legs in the opposite side of the body from the direction they wish to go.  It’s not the most efficient way to get around, but it works for them because it helps keep them safely within the boundary layer of their rock.  There probably aren’t many predators that are going to pick them off of rocks in very fast flowing water either, so moving quickly is not as big of an issue as it is for many other insects.

Other aquatic insects have different adaptations to flowing water.  I’ll discuss some of them in future posts.  Next time, however, I’ll talk about why I call all insects bugs and what a bug really is.

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