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 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:


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


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

6 thoughts on “Friday 5: Aquatic Invertebrates of Southern Arizona

  1. Aquatic insect respiration – and you didn`t include a Water Bug? (Okay, can you tell I`ve fallen in love with Bela, & it`s very unlikely I`ll find anything else important enough to put in the tank that would warrant her release?)
    This evening especially I`ve been watching as she`s been performing a kind of insect aerobics – but instead of pushups with her legs, she`s spent considerable time extending & retracting her breathing siphon (often not even breaking the water surface while doing it). I just hope this is part of normal, happy, water bug behaviour. LOL!
    I will admit the other bugs you`ve chosen do seem very interesting. I sure wish I was one of the lucky students learning from you in person!
    Thanks for sharing your knowledge & your enthusiasm!

    • I have talked about water bug respiration in other places so many times that I feel I have to spread the love occasionally. The other aquatic insects can be just as fascinating!

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