Saturday, November 8, 2014

What do entomologists do?

To tell the truth, we spend quite a lot of time examining male genitalia. It's often the only sure way to identify invertebrates. When two closely related invertebrates evolve forms far enough apart that they can no longer mate with one another (often because the parts no longer fit together), that is one of the definitions that they are separate species. We've been working for the last few years on a photographic field guide to the grasshoppers of Arkansas, trying to make the guide like a bird field guide, that is, making the species identifiable by sight, by field marks that are visible through binoculars, or from close-up photographs blown up on a screen. In other words, so they won't need to be caught and examined under  a dissecting microscope.

You would think that would get me away from all this close attention to genitalia, but actually all it has done is make it more complicated. Now I need to find ways to make the free and untrammeled creature expose its genitalia to me, and I have to get myself into whatever weird angle I need to photograph it from so I can examine it at my leisure on my computer screen.

I've gotten quite good at photographing grasshoppers so that they reveal all (and grasshoppers are surprisingly modest). But this summer I convinced myself I was being a coward by only recording grasshoppers, and not all the other Orthopters, the crickets and katydids. Katydids always seemed to me especially daunting, endless identical green things with long skinny legs and antennae. Capinera's "Field Guide to Grasshoppers, Katydids, and Crickets of the U.S." actually has pages of sonograms for the katydids and crickets, suggesting that since they are out at night and are famous for their camouflage, the only practical way to know which species are around is to listen for their songs. The problem is, at my age most of the high-end bird songs are gone, and I expect I am missing a lot of the katydid and cricket songs as well.

Well, this summer I started on those other orthoptera and I have made some progress, but at the moment I am back to genitalia. There are a few genera of katydids, for example (like Orchelimum or Scudderia) where all the species in the genus look more or less identical to each other. In those cases, the species write-ups in Capinera are presenting me (just as with the grasshoppers) pages of diagrams of genitals.

To show you how it works, here is a male katydid in the genus Orchelimum.

If you note the thing like a carrot sticking out of its rear end, that is one of its cerci (there's another one on the  other side) which it uses to hold the female in place while they are mating. The different species have differently shaped cerci. Here's the chart in Capinera.

What I have to do now is sort of stand on my head so I can get a better angle on the cerci.

And then get in close for a detail shot. (A slight problem is, I am seeing them from below, and the chart shows them from above.)

I have checked the range maps, and luckily only four of the species on the chart (marked by a black dot) are known to occur in Arkansas. Now if you look at the chart, of those marked ones only the second one on the top row, and the first one on the bottom row have the slender unlumpy shape of the katydid in my photograph. Of those two, only the top one has the spur shorter than the remainder of the cercal shaft, the bottom one showing the spur to be longer. Therefore my picture is of O. agile, the Agile Meadow Katydid.

I'm showing you all this to show you how it works. Actually, on this species I am using as an example, there is a simpler way of identifying it: It has a white head and orange-yellow tibiae (the second long joint of the leg). Of the four possible species in my area, only O. agile and one other species, The Black-legged Meadow Katydid (O. nigripes), has a white head, and you can probably guess how the Black-legged differs from the Agile.

This is the only species in our area with black tibiae, so in this case even the female (as here, with her ovipositor) is readily identifiable.

That's two of the four that are found here. Here is a third species.

This has a green head, which means it cannot be one of the first two we looked at. It looks to me like the spur is longer than the rest of the shaft after the spur, which makes it O. silvaticum, the Long-spurred Meadow Katydid.

There is a fourth species, The Common Meadow Katydid, O. vulgare. I think in my heart this is it:

But I can't prove it. I was so intent on photographing it in the act of stridulating, with the "arched wings making a megaphone," as David Ferguson expressed it, that I forgot to get the cerci into the picture.

There are three katydids in the genus Scudderia that occur in Arkansas, all pretty much identical in appearance. Here is Scudderia texensis, the Texas Bush Katydid.

I have shown you a female because this is one of the rare cases where the female is much easier than the male to identify to species. If you look at the ovipositor, the upper margin of the base, and the upper margin of the terminal portion are at right angles to each other. This is true of S. texensis only, females of other species in this genus having a wider angle. But there is no simple way to identify males.

Here is a male Scudderia, found in the same area as the above, with similar coloring, and is very likely also S. texensis, but I can't prove it, since I didn't get a look at the genitalia.

 To identify males, once more I have to examine a chart.

The picture at the top of the chart shows how the rear end of a male Scudderia looks from the side. The six pictures below it show how the sort of tongue-like structure on the top would appear if you were looking straight down on it. The shape at the tip is vital for identification. The three Scudderia species that occur in Arkansas are: On the top row left, S. texensis, Texas Bush Katydid; top row right, S. furcatus, Fork-tailed Bush Katydid; and bottom row left, S. curvicauda, Curve-tailed Bush Katydid.

Now if you look at the live unrestrained katydid in the picture above the chart you will see the problem: All that equipment is permanently concealed beneath its wings.

Here's how we're trying to get around this problem: We were out a couple of days ago and saw a male Scudderia.

I quietly positioned myself behind and a little below him while Cheryl took a long stick and used it to gently lift his wings, and we got these rather rude pictures.

The green thing curving up is what they call the "ventral abdominal process" and the reddish thing it  meets is the "dorsal abdominal process." We see that the dorsal process is bifurcated into two deeply cleft forks with rather meaty side pieces, and the chart tells us this makes it the Fork-tailed Bush Katydid (top row right).

Now I just have to hope the police never search my computer for pornography.