Flatworms!

collecting site

One of my collecting sites.

I collect many of the giant water bugs I use in my research from a spring fed stream in southern Arizona.  It’s a gorgeous place – tons of giant cottonwoods, watercress and duckweed covering the water, and mint lines a good part of the bank so it smells minty as you walk.  The stream contains a lot of giant water bugs, so I am always sure that I can get them at this location whenever I need them.  Even better, it’s almost always cooler at this stream than it is in Tucson, so it’s a nice place to go to escape the heat in the summer!

I often collect other insects at the stream for classes that I teach.  There are a wide assortment of dragonfly and damselfly nymphs, several mayfly and beetle species, sideswimmers (also known as scuds or amphipods), and tons little riffle bugs that skittle about on the surface of the water.  There are also leeches, though these are supposedly not parasitic on humans – and I have yet to get any on me, which makes this seem more likely to be true.  Although the stream bottom is very muddy and it’s common for me to trip and fall into the water or over-top my hip waders, the water’s clean and cool and it’s a really great place to collect aquatic insects.

On my last trip, I was collecting insects for my insect behavior class and pulled out a bunch of wormy looking things that I thought were leeches.  Rather than picking them out and dumping them back into the stream, I brought a few of them back to the lab with me to show my students.  Leeches are the most fantastically disgusting things to watch swim, so I find them fascinating.  However, I went to check the containers the bugs were in a few days later and learned that the things I had thought were leeches were not in fact leeches.  They were something much more exciting: flatworms!

flatworm

A planarian, a type of flatworm. Photo by Mike6271 on Wikipedia.

If you had a good high school biology class like mine (or a good intro biology class in college), you may have encountered these animals before.  We were told they were called planarians, which is the common name for several genera and species of flatworms in the family Planariidae.  You can do some pretty amazing experiments with these very simple creatures.  Those little white spots on the head that look like eyes are not exactly eyes, but they do sense light (and make planarians very cute!).  Because they have light sensing organs, you can train planarians to become attracted to or to avoid certain types of light.  You can also cut them in half and watch them regenerate!  If you cut them lengthwise, you’ll get 2 whole new worms.  If you cut down the middle of their heads, you’ll end up with a flatworm with two heads.  If you cut them across the middle though, you just get two halves of a dead worm.  We chopped our planarians up in one particularly memorable lab in high school, so I know this first-hand.  If you ever have a chance to slice a planarian down the middle, I highly recommend you try it, if only to prove to yourself that it works.

(I can’t even imagine giving a bunch of high schoolers flatworms and a handful of razor blades and letting them loose, but there weren’t any major incidences in my class.)

One of the things I find the most interesting about these worms is how they move.  They are among the most graceful animals I’ve ever seen.  They simply glide through the water.  Even more amazing is their ability to glide along the underside of the surface of the water.  I took some video of the flatworms in my lab a few weeks ago, so take a look.  This video (which I recommend blowing up so that you can see it more easily) shows a planarian gliding along the Rubbermaid container it is housed in, then onto the underside of the surface of the water:

Isn’t that amazing?  I think planarians are incredibly elegant animals, and this is saying a lot for something that is a step away from being a parasite.

If you look down the middle of the worm as it glides on the underside of the water’s surface, you’ll see the digestive tract.  Planarians are predatory, which means they eat other animals.  They use their mouth to secrete chemicals that begin digestion, then suck food into their bodies where they complete digestion.  What you can’t see, however, are the little hairs called cilia that they use to move.  There are tons of these tiny hairs along the undersurface of the worms, which they back and forth like oars to propel themselves through the water.  Because they are moving the cilia and not their bodies, the flatworms appear to be gliding.

You can find planarians in many different kinds of water.  The planarian in the video was collected from that spring feed stream in the desert I mentioned at the beginning of this post.  My high school biology teacher collected them from a storm sewer on the west side of Colorado Spring, Colorado.  All planarians need is a location that stays moist most of the time.  I encourage you to look out for these fabulous little animals.  If nothing else, just watch them for a few minutes as they serenely move about and feel your stress melt away!  But don’t let them trick you into thinking they’re innocent.  They are, after all, looking for animals to devour.

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

Giant Water Bugs Eating

I didn’t post anything last week because I was in the midst of chaos with family and friends, making final preparations for my wedding last weekend.  But now I’m back at the computer and getting things done!  Since I just took a short break, I thought I’d take this opportunity to express my thanks to everyone who’s been keeping up with my blog.  I appreciate your comments and your support!  It’s gratifying to know that something I enjoy doing so much is informative and helpful to others.

Lethocerus indicus eating a small fish

Lethocerus indicus eating a small fish

Today I thought I’d post a short video that illustrates how giant water bugs eat.  Giant water bugs are fierce predators and are known for being able to take down very large prey such as snakes, fish, turtles, and even birds!  Even more amazing is that they accomplish these feats while they barely move at all!  Giant water bugs are called sit and wait predators.  If you think about that phrase for a moment, the behavior it describes should become obvious: giant water bugs sit in one place and wait for prey to swim by.  As much as I love giant water bugs and try to get people excited about them, I’m the first to admit that they sit in one place for long periods of time without moving at all.  In fact, they can even be a bit boring to watch at times.

Abedus herberti

A giant water bug in the pose they normally adopt while waiting for food to swim by.

However, any boredom instantly disappears if the giant water bug you’re watching encounters food!  Part of what makes them exciting to watch is their structure.  I wrote about how to tell the American giant water bug genera apart several months ago and talked about the raptorial forelegs that giant water bugs possess.  Most of the time, you’ll see giant water bugs sitting underwater, holding onto a rock, the bottom of the pond or stream, or a piece of vegetation with only their hind two pairs of legs.  The front legs, those strong raptorial forelegs, are held in front of them, as in the photo above.  If food swims by, they thrust those muscular forelegs forward very rapidly, fold the legs over the food, and then retract their legs back toward their bodies, bringing the prey close to their heads.

The giant water bug then begins to eat its food.  First, it has to find a place it can insert its piercing-sucking mouthparts, that beak that you can see hanging off the front of the head of the bug in the image above.  It will probe the prey item with its beak until it finds a soft place into which it can insert its mouthparts.  The water bug then injects the prey with chemicals that break the tissues down, turning them into a sort of soup.  Finally, the bug sucks the liquid out of the prey and into its own body.  This part is rather like what you do when you take a drink or eat a smoothie with a straw!

Depending on the size of the prey item, the eating part of the process can take a very long time, up to 10-12 hours.  It takes a long time to inject all those chemicals and suck up the resulting soup.  But the prey grabbing happens VERY fast!  So fast that most prey items probably don’t even see the bug before it’s too late.  And so fast that the very first time I fed a bug as a graduate student, I dropped the forceps in which I held the prey (a mealworm) and jerked my hand out of the way as hard as I could.  There may or may not have also been a loud girlie shriek involved, one that I may or may not have been very happy that no one else was in the lab at the time to witness.  :)

So, to get an idea of just how fast water bugs are when they grab food, I recorded my lab bugs the last time I fed them.  Without further ado, I give you a giant water bug (species: Abedus herberti) eating a mealworm!  Pay special attention to how fast the bug grabs the mealworm.  If you look closely, you can also see it probing the mealworm with its beak!  Look for the probing in the space between its eyes and its left foreleg:

Pretty cool eh?  That speed and power in their forelegs allow giant water bugs to catch and eat some very large things.  How amazing is it that an insect, and an aquatic insect at that, can capture and consume a bird?!  And I’m not talking about little birds either.  There is a published report of one taking down a woodpecker.  Now that’s just impressive.

I should be back to my usual posting schedule now, so look for a new post next week!  I’ll be installing an educational aquatic insect pond at the Biosphere II soon, so I’ll be posting about that for sure.  But first, another quick video, this time of a non-insect aquatic invertebrate: the flatworm!

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

Damselflies and Antlions – What’s the Difference?

I get a lot of questions about insects when people learn that I’m an entomologist.  These frequently sound something like, “I saw this little brown beetle in my house the other day – what is it?”  Most of the time, I have a hard time identifying an insect based on a description like this.  You often need to see an insect to properly identify it.  At the very least you need a photo.  There are, after all, close to a million known species of insects and there may be over 10,000,000 insect species in all!  One person can’t possibly know all of the species of insects, no matter how great their memory is.  However, there are some things that I can identify based entirely on a quick and dirty description.  One of the easiest is the difference between a damselfly and an antlion.  They look very similar so I completely understand why people have a hard time telling them apart, but there are some obvious distinctions if you know what to look for.

First, let’s take a look at a damselfly:

damselfly adult

Damselfly adult

This is a member of the family Coenagrionidae, so it is one of the very common little blue damselflies you’ll see around ponds.  What do you notice about the structure of this insect?  Look closely at the wings.  Click on the image to enlarge it if you need to.  How many wing veins and cells in the wings do you see?  The wing veins are the lines on the wings while the cells are the little open square parts between the wing veins.  The color on damselflies is often distinctive.  They fade badly once they are dead, but this damselfly used to be a brilliant blue.  Now look at the head.  Do you see any antennae?  Probably not.  They’re visible (there’s one sticking off the right side of the head right above the right eye, looks like a little hair or a piece of dust), but they’re small, bristly things that most people wouldn’t even notice.  They’re definitely shorter than the length of the head.

Now look at the antlion:

Antlion

Antlion

Can you see why people get these two insects mixed up?  Even some beginning entomologists have a hard time telling the two of these apart!  Look closely at this insect like you did with the damselfly.  First, you should note the color.  This insect is brown, as are almost all antlions.  While some damseflies are brown (especially females), there are many that are brightly colored.  If you have a brightly colored individual with this shape, it’s a damselfly, not an antlion.  Next, look at the wings and observe how many cells there are.  How many do you see?  Antlions belong to the order Neuroptera, the net-winged insects.  Antlions, like other neuropterans, have tiny cells in their wings and a whole lot of them, many more than you’d ever see in a damselfly.  If you see an insect with this shape with tons of little cells instead of 100 or so large, open cells, you’re looking at an antlion.  But the easiest way to tell them apart is by looking at the head.  What do the antennae look like on this insect?  They’re very long, much longer than then length of the head, and thick.  In other words, they’re quite conspicuous, very unlike the tiny, bristly antennae you can barely see in the damselflies.  If you see an insect with this shape that has long, luxurious antennae, it’s antlion.  If it has antennae that are barely visible, it’s a damselfly.  Easy, right?

Of course, there’s one other obvious distinction.  Damseflies are diurnal, which means that they are active during the day.  Antlions are nocturnal, so they are active at night.  You might occasionally find an antlion out during the day, but it’s very unlikely to see a damselfly at night.  Most of the time it’s easy to tell these two insects apart based solely on when you see them!  But, it’s always good to check the length of the antennae and the number of wing veins to be sure.

Now that you know the difference between an antlion and a damselfly, you might start noticing how often these two insects are mixed up.  There is a tank top that I would dearly love to have that depicts an antlion.  The people selling it have it labeled as a dragonfly (not even a damselfly!).  Rubber stamps, especially ones based on old engravings from the 1800’s or early 1900’s, often erroneously depict antlions when they’re supposed to be damselflies.  And all sorts of people feel the need to put antennae on dragonfly and damselfly images.  I don’t know why this is so common, but you will see dragonflies and damselflies with long curly antennae everywhere you look.  This is actually my single biggest pet peeve as an entomologist.  I couldn’t care less about using the word bug when you should use insect, but stick antennae on my favorite insects and you and I are going to have words!

Next time I’ll likely post about how to tell damselfly nymphs apart from stone fly and mayfly nymphs.  They’re easy too, so I hope you’ll check in again soon!

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Text copyright © 2010 DragonflyWoman.wordpress.com

From the Literature: Beetles that breathe through their shells!

I wrote my last three posts on insect respiration specifically because I wanted to talk about a paper that was published in the Journal of Morphology in November 2009 that deals with aquatic insect respiration.  Since this is my personal area of expertise, I find this paper fascinating!  I hope you find it as interesting as I did.

One of the most common insects you’ll see in many freshwater systems is the predaceous diving beetle (Order: Coleoptera, Family: Dytiscidae).  As the name implies, these are beetles that live in water (hence “diving”) and they are fierce predators (hence “predaceous”).  They’re pretty amazing insects in many different ways and many of them are absolutely gorgeous to boot.  However, today I wanted to focus on one really interesting respiratory structure that a pair of researchers in Germany discovered.

Predacious diving beetles are generally atmospheric breathers and must go to the surface periodically to collect oxygen (see my posts on aquatic insect respiration and breathing more efficiently in water for more information).  They then carry air under their elytra while underwater.  Several species expose part of their air bubble to the water to allow them to take advantage of physical gill respiration as they swim around their environment.  However, some predaceous diving beetles are known to stay underwater a much longer time than would be expected if they relied solely on a physical gill.  Some of these beetles have been observed to have little air bubbles attached to their elytra, prompting some researchers to suggest that they might actually be breathing through their shells.

German researchers Siegfried Kehl and Konrad Dettner of the University of Beyreuth were interested in this observation.  They wondered whether certain species of predaceous diving beetles were able to use their elytra as a respiratory organ and set up a simple study to test the idea.  The team was interested in two things.  First, they wanted to know whether the elytra of the predaceous diving beetle Deronectes aubei were able to take up oxygen, that is whether they contributed to the respiration of these insects.  If so, they wanted to examine the structures on the surface of the elytra to determine which structures were contributing to respiration and how oxygen would be transferred from these structures to the rest of the body.

Meet Deronectes aubei:

Deronectes aubei

Deronectes aubei. Photo copyright Christoph Benisch and taken from http://www.kerbtier.de/cgi-bin/deFSearch.cgi?Fam=Dytiscidae.

This is one of the smaller predaceous diving beetles and is just over 1/8″ in length.  This particular species is European and found in Germany, so Kehl and Dettner were able to observe them in their lab.  They discovered that this species is capable of remaining submerged without any access to atmospheric oxygen for over six weeks!  Because these beetles live at the bottom of very fast flowing water, anything they can do to increase their submersion time will help prevent their bring washed downstream and/or damage to their bodies.  Being able to breathe through their elytra and absorb more oxygen from the water would be an excellent adaptation for living in this environment.

First Kehl and Dettner determined whether D. aubei was able to take up oxygen via their elytra using a technique called respirometry.  Respirometry is rather complicated to do and there is a ton of math involved, but the concept is simple.  First, you measure the oxygen content of air or water entering a chamber where an organism is housed, in this case a beetle or group of beetles.  Then you measure the oxygen content of the air or water after it has been exposed to the organism for some length of time.  The difference between the two measurements is the amount of oxygen that the organism used.

Kehl and Dettner measured the oxygen uptake of the beetles from the water using two different types of respirometry.  They also measured the oxygen uptake of beetles in two different treatments.  First they painted a resin onto their elytra, effectively blocking them from taking in oxygen.  Then they removed the resin and measured them again.  To determine whether the beetles were taking up oxygen via their elytra, they compared the oxygen uptake of beetles with the resin covering their elytra (the treated beetles) to the same individuals after the resin was removed (the control beetles).

Both types of respirometry provided the same results: beetles exhibited a significantly larger oxygen uptake when their elytra were exposed to the water than when the elytra were coated with resin and not allowed contact with the water.  These results mean that the beetles are taking up oxygen via the elytra and are using them as a respiratory structure.  The team also found that blocking the physical gill (that air bubble they expose to the water) did not significantly decrease the oxygen consumption of the beetles.  This told them that the beetles are getting most of their air through their elytra and that the air bubble they carry isn’t that important.

scanning electron microscope

The scanning electron microscope I use for my work. The sample goes into the chamber on the left and the image pops up on the computer screen on the right. The electron gun is the cylindrical part sticking up above the sample chamber.

Kehl and Dettner conclusively showed that the beetles were capable of taking oxygen in via their elytra, so the next step was to determine how exactly the elytra are used as a respiratory organ.  To do this, the team examined the structure of the elytra using electron microscopy.  Electron microscopy, like respirometry,  is rather complicated, but for now just know that there are two different types.  Scanning electron microscopy (SEM) is used to look at the surface features of an object and the samples can be pretty big, as large as the sample chamber will allow.  An electron gun is aimed at the object, they bounce off the sample, and sensors collect them to create an image of the object on a screen.  In contrast, transmission electron microscopy (TEM) is usually used to look at the internal structures of an organism, but you can only look at very small portions of the object of interest at a time.  An electron gun is aimed at a very, very thin slice of the thing to be examined and a sensor below the sample collects the electrons that pass through the sample to create an image on a screen.

Kehl and Dettner used both types of electron microscopy in their study.  First they used SEM to look at the surface structure of the elytra of D. aubei.  They discovered that there are three different types of hairs present on the beetles.  One is a simple hair that is found in deep pits.  Another is a hair that is found in shallow pits.  The third is a spoon-shaped hair with an enlarged base that is also found in pits.  Hairs are used for a lot of different things in insects including sensation (smelling and/or feeling the environment around them) and proprioception (determining which body parts are positioned where), so the team used TEM to see which specific hairs were involved in respiration.  They found that the spoon-shaped hairs contained tracheoles that traveled down cylindrical channels in the elytra.  These tracheoles then connected to one of four big tracheae inside the elytra that carried oxygen to other parts of the insect.  This meant that the spoon-shaped hairs were the respiratory structures of the elytra, the areas where oxygen was being taken into the elytra to be used by the insect.

What all of this means is that these beetles have tiny gills littering their elytra that they use to absorb oxygen from the water!  Kehl and Dettner call them setal tracheal gills.  These gills likely significantly increase the surface area through which the beetles can absorb oxygen, allowing them to remain underwater much longer than they could without them.  Because the beetles live in fast flowing, cold water, they live in an ideal aquatic oxygen environment.  These gills allow the beetles to make the most of the abundant oxygen.  The beetles also live in a high risk environment for moving around, so the longer they can stay underwater the better.  Kehl and Dettner suggest that other beetles that either live in very fast flowing waters or that live far under the substrate in streams likely have similar structures as well.  It is common for organisms that live in similar habitats to exhibit similar structural and/or behavioral features that suit the environment, even if they are widely disparate species.  The team predicts that many beetles living under gravel in fast flowing streams might have the same respiratory structures as D. aubei.

I believe that this study is a particularly good one.  Aside from my personal interest in the subject, Kehl and Dettner simply did a great job in creating an elegant study.  First they determined conclusively that the beetles were able to use their elytra to take up oxygen by comparing the oxygen consumption of beetles that were allowed to use their elytral structures to the same beetles when they could not use their elytra for respiration.  Then they used SEM to identify potential respiratory structurs on the elytra.  Finally, they used TEM to determine how the structures on the surface were connected with the internal respiratory system of the beetles, identifying the specific structures involved in respiration and the pathway oxygen takes to get into the beetle’s respiratory tract.  They showed both that the beetles were using their elytra as a respiratory structure and how they were able to do so.  Then they finished off their paper by suggesting the conditions in which this sort of respiration might be particularly well suited and made predictions that could extend to several other species.  It’s an example of a very neat, tidy experiment that uses simple experiments to discover new things with broad implications, which is what ever researcher hopes to achieve with his or her writing.

This concludes my series on insect respiration and aquatic respiration in insects!  If you have any questions or would like more information, please feel free to leave a comment.  Until next time!

Literature Cited:

Kehl S, & Dettner K (2009). Surviving submerged–Setal tracheal gills for gas exchange in adult rheophilic diving beetles. Journal of morphology, 270 (11), 1348-55 PMID: 19480011

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Unless otherwise noted, text and images copyright © 2010 DragonflyWoman.wordpress.com