Friday 5: Capitol Ladybugs

Last Friday I shared my experience at the Smithsonian’s National Museum of Natural History’s butterfly house with you all.  After a delightful end-of-the-day 45 minute session in the NMNH 3D IMAX theater, where we were able to both sit down long enough to rest our very tired legs and watch the movie Flight of the Butterflies about the monarch migration, we were quickly shuffled outside by the guards who were eager to close down the building for the night.  On the way back toward the Metro station, we walked through the Smithsonian’s pollinator garden.  I didn’t see very many butterflies, flies, or bees, but I did see some beetles.  In particular, I saw one type of beetle: ladybugs.  There were ladybugs everywhere!  And there weren’t the kind of ladybugs I was hoping to see either.  There were all Asian multicolored ladybeetles, Harmonia axyridis, an invasive species that was imported from (big surprise) Asia.  In case you missed it, these ladybugs have been featured heavily in the news recently, thanks to a report in Science that suggests that H. axyridis carries a pathogen that actively kills other ladybugs in areas where they become established.  The study looked especially at how the Asian multicolors could quickly kill the seven spot ladybug (Cocinella septempunctata), which I think is interesting largely because the seven spots and Asian multicolors are far and away the most abundant ladybug species I’ve seen in the Triangle Area in North Carolina.  It will be interesting to see if Harmonia will eventually become the dominant non-native species in the area over time if they really are capable of killing their seven spotted relatives.

But back to those Asian multicolors in D.C.!  I took several photos of adult beetles (and I’ll just warn you now: my eyes were completely worn out by the time I took there, so they’re all just slightly out of focus), which I intend to submit to the Lost Ladybug Project over the next few days so I can document my finds.  This one has a lot of big, bold spots:

Asian multicolored ladybeetle adult (Harmonia axyridis)

Asian multicolored ladybeetle adult (Harmonia axyridis)

Asian multicolored ladybeetles get this particular common name (they’ve got others) from their enormous variation in colors and patterns.  You can’t simply rely on spots or colors to indicate that they’re H. axyridis.  See, this one is the same species:

Asian multicolored ladybeetle adult (Harmonia axyridis)

Asian multicolored ladybeetle adult (Harmonia axyridis)

Completely different spot patterns.  Still, there are similarities between these two individuals, especially their very round shapes and the pattern on the front of the thorax.  Not all Asian multicolors have this pattern, but these two individuals had something very similar to this:

Asian multicolored ladybeetle adult (Harmonia axyridis)

Asian multicolored ladybeetle adult (Harmonia axyridis)

If you see a pattern and shape like that, you’re most likely looking at an Asian multicolor.  And did you happen to notice the tasty ladybug snacks lurking on the leaves at the right of the image?  That’s practically a ladybug buffet!

I found three of the four life stages all mixed together on the same plants.  You’ve seen the adults, but now I give you a larva:

Asian multicolored ladybeetle larva (Harmonia axyridis)

Asian multicolored ladybeetle larva (Harmonia axyridis)

When I do my ladybug hunts at work, it is really fun to see the look on the faces of the participants when I hold up the first ladybug larva I find.  By and large my attendees are absolutely shocked that an immature ladybug looks nothing like an adult.  And how cool are ladybug larvae?  They look like bizarre aliens from another world, though perhaps not so much so as the pupae:

Asian multicolored ladybeetle pupa (Harmonia axyridis)

Asian multicolored ladybeetle pupa (Harmonia axyridis)

Now that is one strange looking animal.  Look at all those crazy spikes at the base!  And apparently, a little plague carrying ladybug will eventually crawl out of that pupa and wreak havoc on the local ladybug species…

While it makes total sense that I would find an invasive ladybug species in the heart of an incredibly urbanized area, I was disappointed to see nothing but Harmonia axyridis in the Smithsonian pollinator garden.  I’m sure I am far from the most patriotic person in the U.S., but when you’re in D.C. and on the Mall and taking in the spectacle of all that pure, unadulterated Americaness, it somehow  seems wrong to look at the plants in the garden and see nothing but imported ladybug species.  I wanted some good ol’ ‘Merican ladybugs, gosh darn it!  It makes me a little sad to think that out of the 400 or so ladybugs I’ve photographed over the last few months, I’ve gotten photos of 5 native ladybugs. FIVE!  That’s just terrible.  And those ladybugs up there, cute and aphid-hungry as they are, might be one source of all that terribleness.

And just so I’m not ending this post on a total downer, next Friday I’m bringing you back to North Carolina, where the holly bushes have been blooming.  The insects on the holly flowers: spectacular.  Look for some examples next week!

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

New June Bugs

I wrote about June bugs about a year ago and discussed how everyone has their own idea of what makes a June bug based on where they first learned about them.  I got a lot of responses to that post, people sharing what a June bug is to them, and I loved it!  One person even told me that their June bug was red, something completely new.  My June bug has always been a metallic green beetle, Cotinis mutabilis.  I learned that from my dad, who happened to grow up about 2 hours east of where I live now.  When he moved to the west, he latched on to the thing that most closely resembled the June bug from his childhood and taught it to my sister and me.  When I hear the words “June bug,” I automatically think of that gorgeous metallic green beetle I grew up loving.  Anywhere those beetles live will always feel like home.

Now I find myself in a new place with new bugs – and a new June beetle!  Meet Cotinis nitida, the green June beetle:

Cotinis nitida5

Green June beetle, Cotinis nitida

Moving cross-country meant I had to trade in my childhood June bug for this one.  However, it’s darned close to what I grew up with.  Both beetles are silky, smooth green on top and brilliant metallic green with bronze highlights on the bottom:

Green June beetle, Cotinis nitida

Green June beetle, Cotinis nitida

In fact, this beetle is so similar to the June bug I grew up with I might have mistaken it for the exact same beetle if I didn’t know better.  My western June beetle and this eastern one are quite closely related, and I wouldn’t be surprised if there was an area where they hybridized somewhere between their ranges.  There are some subtle differences though.  One is the color on the back.  Though there is a lot of variation in the colors of the elytra (those hardened upper wings characteristic of beetles) on the eastern species, they tend to be a bit more bronze than the western beetles:

Green June beetle, Cotinis nitida

Green June beetle, Cotinis nitida

They also have little pale patches on their rumps, though these apparently vary in size quite a bit as well:

Green June beetle, Cotinis nitida

Green June beetle, Cotinis nitida

C. mutabilis in the west tends to be mostly to all green on top, lacks the pale rump, and has a slightly longer “horn” protruding off the front of the head.  Otherwise, they’re quite similar in size and shape.

One thing that seems very different to me about this new June bug is the huge number that are out at one time.  There were a few June bugs out when I arrived in North Carolina, about the same number that I was used to seeing in Arizona.  You’d see one or two a day, lazily flying about in the hot, humid air.  Then one day they were everywhere!  I’ve seen thousands and thousands of these beetles flying over the grasses where I work and around the grounds at my apartment complex.  It was like they appeared out of nowhere!  And there were so many of them the even form these little swarms around a lot of trees:

It’s possible that the June bugs in Arizona exploded onto the scene like this too, but I never saw it, and I lived in Arizona for 20 years altogether.  It was pretty amazing to see so many of these beetles flying at once, and they’re still at it!  I have no idea how long to expect them to continue, but I almost always find them swarming around the trees at work.  It’s fantastic!

So, new home = new June beetles.  I couldn’t be happier with either!

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

Friday 5: Aquatic Invertebrates of Southern Arizona

I recently had an opportunity to go aquatic insect hunting for my class.  We had a lot of freedom to do whatever we wanted for the behavior lab, so I decided to do an activity I’ve done many times in my aquatic entomology and insect behavior labs: studying aquatic insect respiration.  It was also the only lab apart from the arthropod lab where my students got to work with live animals, so it was very important to me that I collect a variety of insects for them to choose from.  So, I headed to the mountains south of town and collected as many different things as I could.  Among them were the following five aquatic invertebrates:

1. Red Rock Skimmer Dragonfly Nymph

Paltothemis lineatipes

Red rock skimmer dragonfly, Paltothemis lineatipes

This little guy was a beast to ID because it wouldn’t sit still, but look how cute it is!  Dragonfly nymphs are great predators in aquatic systems because they have the specialized mouthpart you see wrapped around this dragonfly’s face.  It’s a modified version of the labium that they’ve turned into a blood-powered, extensible arm that reaches out and grabs prey with fantastic speed!  I’ve written about the mouthpart in detail in an earlier post, but I think this gives a good indication of how it looks on a skimmer dragonfly nymph – and in a live animal.  Just look at those teeth!

2. Horsehair Worm

horsehair

Horsehair worm

That little curly white thing in the picture isn’t a root or any other plant part and it IS alive!  It’s a horsehair worm, a parasite of crickets and grasshoppers, but some other insects as well.  It’s not entirely certain how they infect their hosts, but once they do they can do some amazing things!  At least one species will eat the host alive from the inside out and, when the host is nearly entirely digested yet still alive, will change the brain chemistry of the host so that it seeks water.  Once there, the worm works its way out of the host and enters the water where it will spend its adult, reproductive life.  These worms are completely harmless to people and I find them rather amusing to watch as they slither about the water.  And, you’ve got to love any parasite that turns its insect host into a zombie that does the parasite’s bidding.  Really cool animal!

3. Backswimmer

Notonecta lobata

Backswimmer, Notonecta lobata

I love backswimmers!  I thought they were some of the coolest insects even before I became interested in aquatic insects and I spent a lot of time watching them paddling around my grandparents’ swimming pool in high school.  In the US  these charismatic little bugs are called backswimmers, a name they get from their tendency to swim upside.  These bugs hunt upside down, collect oxygen upside down, paddle about in the middle of the water column upside down.  Their bodies are perfectly shaped for this motion too with a long keel running down the back.  Some species of backswimmers (though not this one) are even more amazing because they have a hemoglobin-like protein that binds oxygen similarly to the hemoglobin in our blood.  This is thought to allow the backswimmer species that have the protein to adjust their buoyancy so that they can float suspended right in the middle of the water, something almost no other insects can do.  It’s an impressive feat!

4. Painted Damsel Damselfly Nymph

Hesperagrion heterodoxum

Painted damsel damselfly nymph, Hesperagrion heterodoxum

This is the nymph of the painted damsel, Hesperagrion heterodoxum, a bright, multi-colored damselfly as an adult.  There is surprisingly little known about these damselflies, especially considering their showy colors, so about all I can say about this nymph is that it was found in the sort of place you’d expect to find them: a permanent stream in the southwestern US with some emergent vegetation.  I kind of love the expression on this damselfly’s face.  I know it’s not good to anthropomorphize insects, but doesn’t it just look like it knows how cool it is?

5. Whirligig Beetle

Gyrinus plicifer

Whirligig beetle, Gyrinus plicifer

This was a seriously difficult insect to photograph live – they just never sit still!  Whirligig beetles get their name for the whirling, frenetic movement they exhibit as they skim about on the surface of the water.  I’ve talked about whirligigs a bit in the past, but they’re pretty amazing beetles.  Apart from their unique eyes, they also have amazing sensory structures (especially their very sensitive antennae that sense vibrations on the water’s surface – you can see them in the picture), they live in groups, and they have specialized hind legs (broad and flattened for oar-like movement, but VERY short).  Whirligigs are incredibly entertaining to watch too!  They just keep moving and keep moving so that it’s uncommon to actually see one just sitting still.  Fabulous beetles!  I encourage everyone to watch a group of these at some point in their lives.  Trust me – it’s worth it!

I absolutely love having a job where I can go out and collect aquatic insects for work!  Those are some of my favorite days as a teacher because getting outside to collect bugs in a beautiful place like the following is wonderful:

creek

Beautiful cool water, shade on a hot day, and lots of interesting insects.  What could be better?

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

A Trip to Ramsey Canyon

Ramsey Canyon

Ramsey Canyon

The class I’m teaching this semester has very few field trip opportunities compared to the classes I usually teach, so I was very excited to go on the optional field trip this past weekend.  Students who wanted to get some extra experience in the field were asked to meet us on campus at 7:45 on Saturday.  As one might expect, only a handful of the 1400 total students (mostly freshmen) taking the course this semester wanted to get up early to do extra work on a weekend, so very few students signed up.  Then there was a freakish cold front that brought in a frigid rain the morning of the field trip, so even fewer people actually showed up.  But I still wanted to go!  And I’m glad I did.  We went to Ramsey Canyon, a Nature Conservancy property near Sierra Vista, AZ, and it was a really great day.

Ramsey Canyon

New spring foliage in Ramsey Canyon

Ramsey Canyon is a beautiful canyon in the Huachuca Mountains of south central Arizona.  The canyon is rather short by Arizona’s standards.  The walk from the visitor’s center at the bottom to the very end of the Nature Conservancy property is only a little over a mile, and most people never get past the first half mile.  But it is a spectacular half mile!  Ramsey is filled with oaks and sycamores and pines, a gorgeous clear creek full of bugs, bears and squirrels and birds galore.  In fact, the canyon is a very popular birding area thanks to the presence of the elegant trogon and several species of hummingbirds.  I haven’t ever seen a trogon myself, but I’m still hoping to catch a glimpse of one someday.

Coue's deer in Ramsey Canyon

A rare mammal photo on The Dragonfly Woman! Coue's deer in Ramsey Canyon

Our group of 18 staff members and students split into three groups and headed up the canyon to work.  We were there to count Arizona grey squirrel nests, collecting data about the nesting trees and the surrounding area when we found them.  I found a nest shortly after we started up the trail and my group took the required measurements before we sat down for lunch.  Then we didn’t find any more nests.  But that turned out to be fine for everyone in the group!  We kept looking for nests, but everyone pulled out their cameras and we stopped every 10-20 yards to take photos.  Between the six of us I’m sure we took well over a thousand photos.

Ramsey Creek

Ramsey Creek

We also took a bit of time to scoop some insects out of Ramsey Creek with the soup strainer I brought along just for that purpose.  Even though we were technically there to learn about squirrel nesting habits, I think my group ended up learning more about aquatic and other insects simply because we found many more insects than we did squirrels or squirrel nests (though it could have also had something to do with the two entomologists leading the group).

I’ve been to Ramsey before to look for a special aquatic insect that’s found there, a water scorpion with a very limited range called Curicta pronotata.  It’s a glorious insect, more robust than the Ranatra water scorpions I’ve featured several times here, but more stick-like than the more giant water bug shaped Nepa species.  Alas, we didn’t find any Curicta during our trip, but we did find several other things.  We found a lot of these leaf case making caddisflies:

Phylliocus aeneus, caddisfly family Calamoceratidae

I found those on my most recent collecting trip, so you’ve already seen them.  They were incredibly abundant in Ramsey Creek and I caught hundreds (and threw them all back).  It was a lot of fun sharing them with the students because they’re the sort of thing that they would have never suspected was alive if I hadn’t pointed them out.  We found a few diving beetles, including this Agabus species:

Predaceous diving beetle

Predaceous diving beetle, Agabus sp.

I love predaceous diving beetles!  If you ever have a chance to watch some of the larger species swim, I highly recommend that you spend a few minutes admiring their elegance as they paddle about.  It’s truly stunning!  I didn’t find any giant water bugs or whirligig beetles as I’d expected, but we did come across these:

Water striders on Ramsey Creek

Water striders on Ramsey Creek

Water strider nymphs!  Water striders are often gregarious, meaning that they like to stay together in groups.  I really enjoyed watching them skittering around on the surface of the water.  In fact, I recorded them doing so.  If you’d like to experience a taste of what it was like to sit next to a clear, cool creek in a gorgeous canyon photographing water striders, just watch this 30 second video:

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Really, can it get any better than that?  Absolute heaven for me!

Ramsey Creek

Ramsey Creek

It was quite cold almost the whole trip and we were alternately subjected to rain, sleet, hail, snow, and high winds, but it was still a really great day.  I felt like the boundaries between the students and the TAs in our group eventually melted away so that we became a rather cohesive group of photographer scientists out in a beautiful place on a cold and cloudy spring day.  The trip to Ramsey was completely worth getting up early on a Saturday, even if it meant extra work!  At least, it was for me.  I spent the day with a group of very enjoyable people in a stunning mountain canyon teaching and hiking and photographing and watching bugs.  Honestly, I can’t imagine a nicer day in the field!

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


A Monster at the Stream

When I was out collecting aquatic insects with my girlfriends a few weeks ago, I looked up at one point and realized one of our team wasn’t with the rest of us, the ichthyologist.  A few minutes later she came hurrying up the stream, asking where she could find a bug net and muttering about something “enormous” as she zipped past the rest of the group.  She rushed back downstream and didn’t reappear right away, so I figured she’d missed out on whatever prize she was hoping to bag with the net.   It happens.  A lot.  But she eventually came trudging back up the stream, net carefully folded over in her hand, and a big smile on her face.   She said she’d found something amazing and wanted to know if the rest of us, all entomologists, knew what it was.  Then she handed over the net and we saw this amazing beast for the first time:

Campsomeris ephippium

Campsomeris ephippium

Now, I didn’t take the photo with anything that gives you a sense of how big this thing is, but it is far and away one of the biggest wasps I’ve ever seen.  I live in the land of tarantula hawks, so it’s not unusual to see some monster wasp flying about noisily through the air.  I’ve seen a lot of big wasps, some positively enormous.  I’d never seen one like the wasp my friend caught along the stream, but it was impressive even by my high standards.

The size alone was enough to make us all think the wasp was the coolest wasp ever, but there were two other characteristics that added to the excitement.  One was the mouthparts:

Campsomeris ephippium

Campsomeris ephippium

Those things look positively vicious!  When we saw them, we all worried a bit that it might be able to chew its way out of the net as we looked at it, or that putting it into a plastic Whirl Pac (a type of medical specimen bag that is popular for work with aquatics) just wasn’t going to keep it contained.  We eventually transferred it to a hard plastic sample vial for transport back to town, just to be safe.

The other thing I really liked about this wasps was the color.  Just look at the bright orange against the black:

Campsomeris ephippium

Campsomeris ephippium

Gorgeous!  This was a seriously scary looking wasp, but incredibly beautiful as well.  A really excellent find as far as I was concerned!  We looked it up in a field guide when we got back to the car and learned that it was a member of the wasp family Scoliidae, a type of parasitic wasp, and I later IDed it to the species Campsomeris ephippium.   I’ll come back to the biology of these guys in a moment.

I really wanted to photograph the wasp before my friend added it to her collection because it was one of the most impressive things I’ve seen recently.  I set up my little white box, got all my flashes ready, and put the wasp inside.  It immediately started flying around.  It was obviously attracted to light, so it kept trying to fly out of the front of the white box straight toward my face.  I can safely say that having a wasp this gigantic coming for your nose is more than a little scary!  I wrangled the wasp into a bowl to try to calm it down and modified my white box with some spare nylon netting I had lying around so the wasp couldn’t get out of the box as I shot it.

Campsomeris ephippium

Campsomeris ephippium

Then I waited for the wasp to calm down.  And waited.  And waited some more.  It FINALLY calmed down about 3 hours after dark, a good 7+ hours after I put it in the bowl, so I carefully removed the bowl from the white box and started shooting. The flashes woke it right back up and it started flying around the white box, once again kept trying to come out the front.  The netting kept the wasp contained inside the box, but this thing was a beast to photograph!  At one point it landed on top of the flash right as I clicked the shutter release, drowning the wasp in bright light.  That was pretty much that.  The wasp fell absolutely in love with the flash and wouldn’t leave it alone the rest of the photo shoot.  All in all, this wasp was one of the most challenging insects I’ve ever tried to photograph.  What a frustrating little animal to work with!

But look how beautiful this animal is!  The texture on the head is amazing:

Campsomeris ephippium

Campsomeris ephippium

And all that hair!  And those enormously thick antennae!  I love this wasp!

So back to the scientific part of this post.  I can’t just photograph some unknown insect this impressive without looking into it a bit more.  Here’s what I learned about scoliids.  I’ve already said they’re parasites, but they’re a specific type of parasite.  They’re external parasites of beetle larvae, particularly scarabs.  The females apparently burrow into the ground and find the c-shaped scarab grubs, sting them to paralyze them, then burrow even deeper into the ground before constructing a sort of cell for the now immobilized grub.  Then she lays her eggs around the grub.  The developing wasp larvae consume the beetle grub as they develop.  Seems a properly gruesome mode of reproduction for a giant wasp!  What’s even more amazing is they’ll often sting grubs, then decide they don’t want to use them and leave them behind.  These grubs usually don’t fare so well and eventually die without developing further.

I also learned that these are likely a parasite of one of my favorite beetles, my June bug Cotinis mutabilis:

Cotinis mutabilis

Cotinis mutabilis

Seems only fitting that one of my favorite beetles in the world has a big, beautiful, scary parasite to go along with it!

Finding new things is one of the joys of being an entomologist!  Hope I’ll be able to share other exciting finds with you all in the future.

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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

Science Sunday: How Giant Water Bugs Breathe

It’s the start of a new week and you know what that means: Science Sunday!  I thought I’d mix things up a little today by talking about some of my own research.  The subject of today’s post is this bug, a bug that should be quite familiar to my long-time regular (awesome!) readers:

giant water bug

Giant water bug, Family Belostomatidae, Abedus herberti

This is Abedus herberti, a giant water bug in the family Belostomatidae within the order Hemiptera (true bugs).  It’s a large, aquatic insect native to Arizona and northern Mexico that you’ll find in streams, often in the mountains.  It’s an interesting bug for many reasons, but it is especially well-known because the male bugs care for the eggs until they hatch (see my post about giant water bug parents for more details!) and they are wickedly efficient predators.  These traits make these bugs fascinating for entomologists like me, but they’re not what got me interested in giant water bugs originally.  I got excited about giant water bugs because of this:

Abedus herberti at surface

Abedus herberti at surface, collecting air

Respiration!  I never thought I would ever work with either insect respiration or aquatic insects (except dragonflies), but this project opened up a whole new world of possibilities to me and completely changed the direction of my research.  So, today I’m going to tell you  about the project.  It’s too long for one post, so this week I’ll give you an overview of the respiratory behaviors of Abedus herberti and next Sunday I’ll talk about the experiments I did to show that this is a respiratory behavior.

Giant water bugs are aquatic insects and, as such, have several adaptations that allow them to live in water.  I’ve talked about aquatic insect respiration before, so I’m not going to go over the respiratory adaptations again here, but note that giant water bugs depend on air to breathe.  Water bugs in the genus Lethocerus have a long respiratory tube (called a respiratory siphon) that they stick out of the water that works a lot like a human using a snorkel.  They also have a small space under their wings that holds a small amount of air so they can breathe underwater for a short time.  (Imagine using a SCUBA tank – same deal!)  Abedus herberti does things a bit differently.  First, the respiratory siphon has been reduced to short air straps:

air straps

Abedus herberti. Arrow points to the air straps.

Second, it has a much bigger space under the wings.  That means it can carry more air with it underwater and can remain submerged a lot longer.

So how does Abedus herberti breathe?  Let’s trace the behavior from the moment the bug sticks its air straps out of the water, fills the space under its wings with air, and dives into the water to settle near the bottom.  The bug then follows one of three behavioral pathways.  The simplest is this: the bug absorbs oxygen from the air bubble into the body.  When it has used up most of the oxygen, it goes to the surface to replace the bubble.  If the bug’s close enough to the surface, it simply raises its abdomen and sticks the air straps out.  If it’s in deeper water, it stretches as far as it can to try to reach the surface without letting go by raising the abdomen up, releasing the hind and middle legs, and holding on with only the front claws.  If that’s not enough, it will let go completely, float to the surface, and quickly replenish the air store before diving to the bottom again.  You can see the behavior in this rather blurry video:

That’s one behavioral pattern.  In the second pattern, the bugs add one more step: gaping.  The bugs surface, dive, and sit at the bottom, using the oxygen in the air bubble as before.  However, after about 5 minutes they expose the air bubble to the water.  To do this, they lower the abdomen, creating a space between the abdomen and the wings:

Abedus herberti

The giant water bug Abedus herberti gaping, exposing its air store to the water. The silvery part is the air bubble.

Gaping is a tiny behavior, one very small movement, but it does so much for the bug.  By exposing the air bubble to the water, the bug transforms the air bubble from a simple oxygen store into a physical gill capable of absorbing oxygen directly from the water, tripling the length of time it can remain underwater!  The bugs may gape for 20 minutes, then close the gap before returning to the surface.

The third behavioral pattern adds one important step: dynamic gaping.  This pattern starts with the bug surfacing, diving, sitting on the bottom, and gaping.  After gaping for 5 or more minutes, the bug starts doing this:

They do this motion over and over and over for up to three hours.  Gaping allows the air store to become a physical gill, but dynamic gaping makes the physical gill function as efficiently as possible by stirring the water around the bubble.  This pushes oxygen-depleted water away from the bubble and draws in oxygenated water.  The physical gill is much less efficient at absorbing oxygen from the water when the bug gapes, but does not dynamically gape.  Dynamic gaping is thus a form of ventilation that allows the bugs to remain underwater ten times longer than they can without gaping or dynamically gaping!  But even a dynamically gaping bug must eventually return to the surface (see my post on better breathing underwater to learn why), so it closes the gap between the abdomen and wings and surfaces.

The advantages of this behavior are clear: gaping allows the bugs to remain underwater 3 times longer and dynamic gaping ten times longer than they can when they do not expose the air store to the water.  But why is it important to stay underwater?  This is one reason:

egret

Egrets and other wading birds like to eat water bugs!

Many things love eating large, protein filled insects, so staying hidden underwater as long as possible likely helps A. herberti avoid predators.  However, the bugs carry a lot of air with them, which makes them very buoyant. If they let go of the bottom, they float immediately to the top.  Diving is probably very hard too because they have to fight against their tendency to float to the surface.  So, if the bugs benefit from remaining underwater, but it’s hard to stay underwater, then it’s a good idea to stay underwater as long as possible.  Gaping and dynamic gaping to the rescue!  These two simple, easy behaviors greatly extend the length of time the bugs can remain submerged, but the behaviors probably also require far less energy than diving from the surface.  If so, then gaping and dynamic gaping help the bugs avoid predators, save energy by avoiding trips to the surface, and maximize the time the bugs can spend trying to capture food.

So that’s gaping and dynamic gaping!  Next week, I’ll discuss how I know that these are actually respiratory behaviors.  I hope you’ll check back for part two!

Literature Cited:

Goforth, C. L. and Smith, R. L.  2012.  Subsurface behaviours facilitate respiration by a physical gill in an adult giant water bug, Abedus herberti.  Animal Behaviour: doi:10.1016/j.anbehav.2011.12.02.  (Published online only currently – will replace this with the print citation when the issue is released)

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