Saturday, August 13, 2016

Spot Check

Narrow-winged Tree Crickets (Oecanthus niveus) are a common singer in NE Ohio. I know them well. I’ve found them singing between two leaves in many small trees, lower down in larger ones, in vines and shrubs, and even occasionally in meadow vegetation. 

In more urban areas such as where we live, they often sing with the Snowy Tree Crickets in our yards. (In fact, I'm listening to both species outside the window as I write.) It’s easy to tell them apart, as the Snowy Tree Cricket’s short, rhythmic, chirp-chirp-chirp song is easily distinguished from the slightly longer songs of the Narrow-winged. 

Their wings do seem a little more narrow than other crickets in their genus, and they have reddish or rich orange caps on the tops of their heads. 

And then there’s the antenna spots. That’s the reliable way to tell these Oecanthus genus cricket species apart. Not that they are happy to show their little antenna spots to me - or to you. It’s a challenge to get close enough at just the right angle!

I haven’t been too concerned about that, though, because I know my Narrow-wingeds. The red spots on their heads are obvious enough, and when I've checked the antenna spots, they clearly curve to form either a forward or reverse “J.”


Davis’s Tree Crickets are another matter, however. They're not nearly as common as the Narrow-wingeds, and I don’t generally come across this species. They live up in the trees, far out of reach of anyone who wants to see them at all, not to mention look at their antenna spots. The Latin name is Oecanthus exclamationis, because the spots form an exclamation mark! But again, that’s if you can: 

a. find a Davis’s Tree Cricket
b. get one down from the trees so you can look closer
c. maneuver him so that you can see his antenna spots.

Just listening, though, shouldn't be a point of confusion. Their songs are longer with more erratic pauses than those of the Narrow-winged Tree Crickets. The Singing Insects of North America web site describes the Davis’s songs as “a melodious trill irregularly interrupted, usually briefly and often after the trill has continued without interruption for >5 sec.”

The Narrow-winged's song, however, is “a melodious trill interrupted briefly at intervals of 5 sec or less. Interruptions are not synchronized, so when several males are calling the sound becomes continuous. Easily confused with the songs of two-spotted and Davis's Tree Crickets, but trills by these species are interrupted at longer intervals and have faster pulse rates.”

This all played out in a most unexpected manner at Bath Nature Preserve in Summit County, Ohio, where I’m doing a cricket and katydid study for the University of Akron Field Station this summer. The parking area's small trees are exactly the size that Narrow-winged Tree Crickets often seem to prefer. There are two young swamp white oaks, a pin oak, a sweet gum, and what might be a crabapple, though I’m not entirely sure. 

Those Narrow-wingeds were singing up a storm in the two swamp white oaks. I couldn’t get too close to the actual singers, but I saw a couple of females that had red head patches, and the males were singing the repetitive songs of the Narrow-wingeds. It sounded a little lower in pitch than I might have expected, but I didn’t have any for a comparison. The phrasing was what I expected for Narrow wingeds. 

I took some photos shooting upward from below the singers, and declared them to be Narrow-wingeds. After all, that’s who the females were. Here are some antenna spots of the individuals I checked – I think you can see how they curve to form the diagnostic forward or reverse “J.”

Imagine my surprise when it was later brought to my attention that  the two loudest singers might actually be Davis’s Tree Crickets! 

What? No, really? But Nancy Collins, who has specifically studied tree crickets for years and even discovered a new species, encouraged me to take a closer look at my singers.

Somehow, I would need to find the antenna spots of crickets who were singing in the dark up in the trees

I wasn’t entirely committed to putting a step ladder in my little car and pulling it out in the parking lot, so I was going to have to try using my insect net very gently in the branches. I feel strongly about being sensitive to insects and returning them unharmed where I found them, so the net was going to take some maneuvering.

And I succeeded! I got the singer I had recorded, and…here are his antenna spots:

It’s an exclamation mark.

So… both Narrow-winged AND Davis’s are in these little trees! I checked some additional crickets, and I did indeed find both species, including singing males. My species confirmations came through recording a singer, catching him gently in one of my trusty Parmesan cheese containers...

...and then trying to get the right angle for an antenna spot photo.


And what about the songs? What I'm finding is that if both species are singing together, the Narrow-winged Tree Crickets will be a whole step (major 2nd ) or a minor third higher than the Davis’s. Here's the Narrow winged in swamp white oak #2, then at least two Davis's in swamp white oak #1 (the larger of the two). They are singing at exactly the same temperature.

If there’s just one species singing, though, I won’t have the benefit of comparing the pitch relationship between them.

Remember, too, that all of these crickets sing lower and slower when the temperature is a little cooler, and warmer and faster when it’s warmer. The pitch of their songs will vary even during the course of an evening as temperatures change, and I'll need to learn how the relationships change as that happens.

But now I know that Davis’s Tree Crickets don’t always sing longer songs with erratic pauses. They can sing with a steady rhythm that is similar to the Narrow-winged Tree Crickets. Here's my initial recording that you heard earlier:

They don’t have to be high up in the trees, either, though that’s their common habitat. Why do those little swamp white oaks in the parking lot please these Davis's? I have no idea.

In time, I hope to be able to reliably identify Davis’s Tree Crickets by ear, even if there are no Narrow-wingeds with which to compare them. But for now, this is a new - and interesting – project, and Bath Nature Preserve is the place to study the songs.

Monday, July 18, 2016

The Predatory Katydid

The Protean Shieldback. That’s truly the name of this armored tank of a katydid. If you saw one, you probably would not even think it IS a katydid, and you’d certainly never guess that it’s a little predator.

Shieldbacks are almost always brown, which is appropriate for their habitat. They live at woodland edges and shrubby fields, climbing up onto shrubs and other vegetation after dark. They look carved from wood - even the female's ovipositor! 

Underneath (if you get the opportunity to look), you'll find a rich, contrasting yellow.

Why are they called shieldbacks? Take a closer look. Doesn’t that appear to be a little shield?

And those bodies! They certainly don’t resemble the long-winged Scudderia bush katydids, like this Curve-tailed Bush Katydid on a nearby leaf.

In fact, it’s hard to imagine how the males can make enough sound to be heard with those little wings projecting from below the shield, but they certainly manage quite well. 

 Here’s the Protean Shieldback's song:

There are three shieldback katydid species in Ohio, and I suspect the Protean is the more common. Up here in NE Ohio, we seem to be more likely to find Least Shieldbacks, though they occur elsewhere in the state as well. They look similar and I don’t think there’s anything “least” about them. The American Shieldback’s range map indicates that they could be found in southern Ohio.

The Least Shieldback’s song is a series of short little bursts that occur in a consistent rhythmic pattern:

In contrast, the Protean Shieldback’s song is longer, with brief pauses between songs. (Far below the Protean Shieldback, you'll see the songs of Cope's Gray Treefrogs, which are present in southern Ohio, but not in NE Ohio.)

The songs are not necessarily consistent in length; the songs of the Least Shieldback are more rhythmic and predictable. Because this is the one shieldback species that has a song with long phrases and very short pauses, it’s rather easy to identify.

The only song I have to listen closely for is the Rattler Round-winged Katydid. The Rattler's songs are both short and long phrases, and are often two short bursts followed by a much longer phrase.

When I play them in isolation, there’s no confusion, but when a number of katydids are singing in the meadow or edges, songs can overlap and cause some confusion. I try to focus on the different tone quality of the Rattler Round-winged. 

Were they singing in the same habitat? Of course – at times they were almost next to each other!

We have one other shieldback that is common in NE Ohio, though I don’t know how far south this little non-native species has traveled. I wrote about Roesel’s Katydids a couple of years ago, and you can read about them here. They are varying degrees of brown and green, and look quite different from our big, burly native shieldbacks.

As we did last year, Wendy and I have been visiting Buzzards Roost Nature Preserve in the Ross County Park District near Chillicothe in southern Ohio, and delighting both the gorgeous preserve and the singing insects that we don’t have up in the Cleveland area. 

Protean Shieldbacks can easily be found there from at least June 22 into July. On our most recent trip over the July 4th weekend, we saw quite a few. It’s was quite unlikely that we’d see them during the day. After dark, however, they suddenly appeared.

Although it was very challenging to manipulate both my body and camera to photograph them in the dense vegetation, sometimes the shieldbacks themselves were in convoluted positions. This mating pair's balancing act didn’t even look possible, especially for two hefty, chunky insects!

The most fascinating part of the evening was finally seeing an example of their predatory behavior, which I'd read about but never observed. Many katydids will eat an occasional small insect if the opportunity presents itself – I once saw a Short-winged Meadow Katydid eating a damselfly – but shieldbacks are hunters.

At first, I thought this female Protean Shieldback on the same leaf as two mating Japanese beetles was just passing through.

I thought it looked a little crowded on that leaf until I realized why she really was there: 

She was planning her dinner!

Only once have I heard and seen Protean Shieldbacks in NE Ohio, but I know it's a possibility. I've only found Least Shieldbacks a few times over the years, too. Still, I'll keep listening and looking every summer, and I know I can visit them in southern Ohio.