Thursday, February 20, 2014

Fork-tailed Bush Katydid

I vividly recall an episode in my childhood that perhaps cemented my fascination with insects. I must have been somewhere between eight and eleven years old. One afternoon in late summer I heard an insect calling at regular intervals from a rhododendron bush outside the front door of our Portland, Oregon home. I finally tracked down the creature and discovered it was a male Fork-tailed Bush Katydid, Scudderia furcata. What happened next I shall relate later in this post.

I did not know at the time what kind of katydid I was observing. Years later I discovered E. O. Essig’s book Insects of Western North America in our public library and found the species there. Indeed, it was virtually the only option for western Oregon, Washington, and southern British Columbia.

Eight species of bush katydids in the genus Scudderia are now recognized in the United States and southern Canada. The Fork-tailed Bush Katydid is by far the most widespread, being transcontinental in its geographic distribution. Still, in most regions it is next to impossible to separate from other species.

The only reliable way to differentiate Scudderia species is by the shape of the “dorsal process” or “supra-anal plate” in adult male specimens. This horn-like feature juts out of the top of the abdomen at the rear. Another structure, the “sub-genital plate” curves up from below to meet the supra-anal plate. The sub-genital plate may at first be mistaken for an ovipositor, an organ found only in female katydids.

Not surprisingly, the shape of the dorsal process in the Fork-tailed Bush Katydid is, well, fork-like. It looks like a miniature tuning fork, as revealed in the image above. Images of wild, living male bush katydids are usually impossible to identify to species because the folded wings usually conceal the supra-anal plate.

Males also possess the “file and scraper” modifications on the “shoulders” of their front wings. These are the structures they rub together quickly to produce songs. Bush katydids typically rasp a short, intermittent call: s-s-s-s-s-S-S-S-T. This discontinuous song no doubt helps prevent predators from pinpointing the location of the insect.

Back to the opening story. I saw the male katydid produce its song, and in short order a female flew in to join him. Both genders, once close to each other, will talk in soft “ticks,” but I do not recall them having such a conversation. The next thing I knew, the two were in copula, “tail-to-tail.” I watched in horror as I saw a white, gelatinous mass oozing from between the two. When they finally separated, it appeared the female had been torn open and was losing her innards.

I learned much later in my life that the male was the source of this mass. Male katydids and related orthopterans transfer a protein-rich spermatophore in the process of inseminating a female. She consumes this object while the male’s sperm enter her oviduct.

Scudderia sp. female

Fertilized female bush katydids use their curved, knife-like ovipositors to insert eggs between the layers of a leaf, at the leaf’s edge. The result is a kidney bean-shaped bulge in the leaf. A female can lay up to 175 eggs, but deposits a small quantity at each location. The following spring, a tiny katydid emerges from each egg.

Scudderia sp. nymph

Nymphs go through six instars (an instar being the interval between molts), gradually accruing wing pads and both internal and external reproductive organs. They are general feeders on the foliage of shrubs. They are sometimes considered a pest in orchards and citrus groves when populations build to high levels (Bentley, 2002 and Headrick, 2000).

Adult S. furcata are 36-40 millimeters from the head to the tips of the folded wings, so they are not small insects. Still, they are incredibly well camouflaged. Most specimens are wholly green, but late-autumn specimens are correspondingly brownish, reddish, or even pink. They are most active at night, and are sometimes drawn to outdoor lights. Both sexes fly well.

Katydids in general are among my favorite insects, and I can’t help but wonder if that mating pair forever endeared them to me. Keep a listen for katydids in your own yard, garden, or neighborhood park. See if you can tell different species apart by their songs. Search with a flashlight and you will eventually find one of these amazing insects.

Sources: Bentley, Walt. 2002. “Researching Biology and Control of Forktailed Bush Katydid (Scudderia furcata Brenner) and Western Spotted Cucumber Beetle (Diabrotica undecimpunctata howardi Barber) in Stone Fruits,” California Tree Fruit Agreement Research Report 2002 .
Bland, Roger G. 2003. The Orthoptera of Michigan – Biology, Keys, and Descriptions of Grasshoppers, Katydids, and Crickets. East Lansing: Michigan State University Extension, Extension Bulletin E-2815. 220 pp.
Elliott, Lang and Wil Hershberger. 2007. The Songs of Insects. Boston: Houghton Mifflin Co. 228 pp (and a CD).
Headrick, David. 2000. “Fork-tailed Katydid Studies,” Citrus Research Board 2000 Annual Report.
Helfer, Jacques R. 1972. How to Know the Grasshoppers, Cockroaches, and Their Allies (Second Ed.). Dubuque, IA: Wm. C. Brown Company Publishers. 359 pp.

2 comments:

  1. Hahaha! I guess it was either going to be a fascination or a phobia!

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  2. One of these little critters snuck into our bedroom last night; kept me awake the whole night through! Caught it in the morning and released it in the front yard. Beautiful little green bug.

    Rick
    Portland, OR

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