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Predation pool

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Predation pool, a tinaja in the Rincon Mountains. Julia posing next to the deer leg.

Predation pool, a tinaja in the Rincon Mountains. Julia posing next to the deer leg.

How horrible would it be to have your insides sucked out by a giant insect? Last Saturday I watched a dramatic reversal of what I usually think of as the food chain.

I was hiking down a bedrock wash in the Rincon Mountains, east of Tucson. Julia, who has been working with me at my field sites, was right behind me.

“There’s a snake!” she called out as I launched myself over a tinaja, or small pool of water that had formed in the rock over the course of several large monsoon storms.

Concerned it might be venomous, I stopped.

“Where?”

“In the water,” she answered, squatting down by the pool. “Hey, it’s eating a bug!”

I bent over the pool, too, and saw a  writhing, twisting, gymnastic battle being waged below the surface. The garter snake (genus Thamnophis) was about 10cm long, or the size of a pencil. It was locked in combat with a water bug (genus Lethocerus) that was about 3cm long and half that wide. (Both were probably juveniles, as garter snakes can grow to be over a meter long as adults, and the bug lacked the wings of the adult stage.)

“No,” I said. “The bug is eating the snake.”

The bug’s jaws were attached to the throat of the snake, which wriggled and knotted and looped itself, trying to throw off the predator. Of course at that point I dropped my pack and snatched up my camera.

I’ll let you watch how that ended up on my raw footage:

It was pretty horrifying to watch, really. I was empathizing with the snake, being a vertebrate and all. If I remember correctly, the belostomatid mouthpart pierces prey, releases digestive enzymes, then sucks up their dissolved innards through a straw. What a way to go.

The other fourth (?) instar Lethocerus individual was still perched at the surface, rear end in the air to breathe, ready to pounce on whatever fell next into the tinaja.

The other fourth (?) instar Lethocerus individual was still perched at the surface, rear end in the air to breathe, ready to pounce on whatever fell next into the tinaja.

But why did I have to be horrified? Why could I not be rooting for the bug, who clearly was suffering from competition in that little pool? I never panned the camera over to it, but another identical Lethocerus was sitting just 30cm away, just waiting for something else to fall in to the pool. I bet the bug that got the snake had just been poised on a hair trigger, thinking, “the next one’s mine, the next one’s mine!” It was probably starving. After leaping without even looking, I wonder if it got that look in its little compound eyes that I get when I start rock climbing on a route that is way too technical for me: that look of “Oh well, all I can do is hang on, now!” And its big risk paid off with a Thanksgiving feast – did it feel a rush of relief, or satisfaction? That may be a neuroscience or even philosophical debate for another post.

I have to admit also to being fascinated at the strategies of size-class vulnerability to predators (little snakes are vulnerable to bugs, but I bet bigger snakes even eat those toebiters), the differing predation strategies of the snake that cruises around hunting and the insects that lurk in the shallows and pounce, and the avoidance behavior of the snake that I probably disrupted by leaping over the tinaja and scaring it into the water without due caution.

Oh yeah – to add a macabre touch at the end of the video, as I packed up my camera, I lifted my backpack and realized in my haste I had dropped it on a deer leg, fur and hoof still intact. We had found the predators’ pool. (Hope the water bug didn’t take the deer down, too!)

The victorious Lethocerus hauled its prey deeper and away from its conspecific competitor to feed.

The victorious water bug hauled its prey deeper and away from its conspecific competitor to feed.

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Written by pacificsummer

September 17, 2013 at 11:16 pm

Posted in Uncategorized

3 Responses

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  1. Gnarly – I’ve never seen one of the beetles hunting before!

    bblonder

    September 18, 2013 at 12:46 am

  2. Holy cow! I might never swim in the desert again ;) Seriously though, your video made me glad that the era of giant arthropods is long past!

    Loren A

    September 18, 2013 at 8:20 am

  3. awesome footage, I love these bugs. I used to pick them up and play with them before I learned what a painful bite they have. Luckily I was never bitten by one.

    zakgezon

    September 18, 2013 at 9:58 am


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