The hardest part

While my own waiting period has nothing to do with guns, I am always reminded of this scene from The Simpsons whenever I have some waiting to do. Come to think of it, that Tom Petty song usually springs to mind as well.

Not surprisingly, my own waiting game comes from my spider samples. The species that I collected in Panama turned out to not belong to the genus Freya after all; it was identified as Frigga crocuta by Yinkiria L. Cheng of the University of Panama. An interesting outcome of that identification is that “crocuta” is the Latin word for hyena, and I just finished writing a story about a boy who can turn into that particular animal.

I'm really not sure where the resemblance lies between a possibly vegetarian spider and this predator, though...
I’m really not sure where the resemblance lies between a possibly vegetarian spider and this predator, though…

As I mentioned in an earlier post, one visual confirmation of Frigga crocuta harvesting food from a plant isn’t nearly enough to establish whether this jumping spider (salticid) is truly vegetarian;  I need a lot more evidence than that. One of the most helpful tools that science can provide is called stable isotope analysis, in which I use a machine known as a mass spectrometer to determine the levels of nitrogen-14, nitrogen-15, carbon-12, and carbon-13 in a dried spider’s body.

Now most people have heard of nitrogen and carbon at one time or another, since nitrogen comprises approximately 79% of the air around us and diamonds and graphite (along with coal) are all made of carbon. Given that many of our more complex molecules, like proteins, sugars, lipids (fats), and DNA, also contain large numbers of carbon atoms, all life on planet Earth is said to be “carbon-based.”

Liquid nitrogen is also used in all sorts of science demonstrations.
Liquid nitrogen is also used in all sorts of science demonstrations.
If robots or computers ever reach the point that they can be considered alive, they would be considered silicon-based life forms.

But what do those numbers mean?

It all comes down to that most basic building block of matter, the atom.

Ignore all of the mistakes in the image here. The electrons are too big and they aren’t supposed to orbit the nucleus, the number of electrons doesn’t equal the number of (red) protons in the nucleus, etc.

The main point to understand it that all atoms are composed of protons, neutrons, and electrons, and that it is the number of protons that determines the classification of any atom. Neutron numbers, however, can be different. If we consider a proton to have the atomic mass of one and the neutron to have about the same (even though it’s really a little more massive), then we would expect an atom with 7 protons and 7 neutrons to have an atomic mass of 14, which therefore makes it nitrogen-14. Add an extra neutron, and you still have nitrogen, but the mass is now 7+8=15, so it’s nitrogen-15. In carnivorous animals, the levels of nitrogen-15 increase based on the percentage its of diet based on animal matter, so Frigga crocuta, if it is indeed vegetarian, should have a lower level of nitrogen-15 than other spiders. This was the case with Bagheera kiplingi when it was studied in 2007-2009, as can be seen in the graph below:


Screen Shot 2014-11-23 at 5.18.21 PM
Note how the level of nitrogen-15 is much lower in Bagheera kiplingi (green circles) than it is in other spiders (red squares). For the full text of this article, please click here.

The other isotope, or atom with different numbers of neutrons, that appears on this graph is carbon-13. Like nitrogen-14 and nitrogen-15, these two types of carbon differ on the number of neutrons. In the case of carbon, carbon-12 has 6 protons and 6 neutrons, while carbon-13 has 6 protons and 7 neutrons. You might’ve already guessed that the more famous carbon-14, which is unstable and used for radioactive dating, contains 6 protons and 8 neutrons.

Carbon-13 levels are usually consistent between a food source and the consumer of that food, which means that carbon-13 levels in the Beltian bodies of Vachellia plants are very close to the Pseudomyrmex ants and Bagheera kiplingi that consume them. This is the reason why B. kiplingi‘s green circles are right above the yellow-orange rhombuses of Beltian bodies and the purple triangles of Pseudomyrmex ant workers, because their levels of carbon-13 are all approximately the same. If I see a similar profile in Frigga crocuta, then it will be a powerful support for my hypothesis that this salticid is also a vegetarian.

To perform stable isotope analysis for the dried spiders that I brought back from Panama, along with some old samples of Bagheera prosper that I collected in Oklahoma and Texas during the summer of 2013, I was fortunate enough to find the Academy of Natural Sciences of Drexel University in Philadelphia, PA.

A view from the outside on the day I started my sample preparation. Unfortunately, it was rainy, so the photo looks kind of dark. Those two dinosaurs in front at the bottom (Deinonychus antirrhopus) should also be feathered, but nobody knew that when the statue was cast.
Some of my dried spider samples had been sitting in plastic test tubes for more than a year.
They still looked like spiders, though.
I also had Pseudomyrmex ants that I brought back from Panama and Costa Rica.


These samples all needed to be prepared for analysis in the mass spectrometer, which is a large, freezer-sized device that burns tiny samples of organic material and uses the resulting gas to determine the levels of each isotope.

When I say “freezer-sized,” I mean one of those giant freezers one uses to keep 20 turkeys frozen, not the kind that sits on top of a refrigerator.

For such a large piece of equipment, the mass spectrometer works with really tiny samples. Most of them were just around one milligram, or one thousandth of a gram. Since a gram is about the same weight as a paper clip, you can get an idea of how small these samples were.

Each of these samples was loaded into a tiny cup of aluminum foil called a “boat.” It’s the little thing sitting in the metal dish.

Since even a jumping spider weighs far more than a milligram, I took my samples by pulling off each spider’s legs. Now before you accuse me of being cruel, remember that these salticids were dried many months ago. Sure, you can accuse me of being cruel on that part (even though I definitely didn’t enjoy it), but this part didn’t cause any pain to the spiders, because they were already dead. Besides, this was all with the goal of advancing our scientific knowledge. If these spiders happen to be threatened by habitat loss some day, I’m sure that people will be more eager to protect vegetarian spiders than the old carnivorous kind.

Some people might like the spider that kills snakes… although both spiders and snakes get a bad rap, if you ask me.


On that note, I’ll mention that there is an organization trying to help preserve the ladybird spider in the United Kingdom (even though that salticid, like most jumping spiders, is a predator).

Although I’d still say that it’s definitely cute!

My samples took two days to prepare, and I am very grateful to everyone at the Academy of Natural Science’s Environmental Biogeochemistry Section for all of their help.

All of the samples are now ready to run!
All of the samples are now ready to run!

The next step is to wait for the samples to be processed, which I know will take some time. I’ve also applied for funding to continue my research from a scientific research organization, and I’m considering running a crowdfunding campaign to continue my investigation, but I need to realize that all of these things can’t happen right away!

So the waiting really is the hardest part.

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