Thursday, February 21, 2013

OrThoptera Thursday: Greater Angle-wing Katydid

One of the joys of summer nights in North America, at least east of the Rocky Mountains, is the songs of katydids. Among the more abundant and widespread of our many native species is the Greater Angle-wing Katydid, Microcentrum rhombifolium.

This is a very large insect, adults reaching 52-63 millimeters from head to folded wingtip. Females in particular are also very heavy. Let one crawl across your hand and you will feel how weighty she is. Both genders are uniformly green throughout, somewhat mottled on the legs and face. This species is among the most “leaf-like” of our katydids and is found mostly in deciduous trees.

The Greater Angle-wing ranges from Pennsylvania and New Jersey south to Florida, west to southeast Minnesota, Iowa, southeast Nebraska, Kansas, and Texas. It also wraps around the southern tip of the Rockies and Sierras, north to San Francisco Bay and throughout Arizona and much of Utah.

Adult males of this species produce two kinds of songs. The first is a “calling song” that consists of a loud “lisp” repeated an average of every two to four seconds. Producing an intermittent song like this probably prevents predators from easily locating the insect. I know it has frustrated me on a number of occasions and I have better than average hearing. Once a female is attracted, the male switches to a “courtship song” that is a series of “ticks.” The female is capable of answering this call, though she does not have the well-defined sound-producing structures the male has. The male eventually moves to find the female via this “conversation.”

Contrary to popular culture, katydids do not generate their song by rubbing their legs over their wings. The front wings of the male are modified at the “shoulders” to include a file on one wing and a scraper on the other. The file is composed of a row of peg-like teeth over which the scraper is stroked rapidly. This method of sound-production is termed “stridulation,” and the part of the wing modified is called the “stridulatory area.” Both genders hear the songs through slit-like openings on the front legs.

Once male and female are together, mating may take place. This involves the transfer of a sperm packet known as a spermatophore, produced by the male. The spermatophore is a fairly substantial ball of gelatinous protein surrounding the sperm sac itself. Once the pair disengages, the female will eat the protein mass while the sperm enter her oviduct.

The first time I witnessed mating in katydids, I thought something horrible had happened to the female, that her internal organs were oozing out of her body! The edible gift provided by the male may help foster the development of her eggs, and/or encourage her to rebuff subsequent suitors, thereby insuring it is his DNA that is carried through to the next generation.

One additional, odd note. I observed a trio of Greater Angle-wing Katydids in south-central Ohio in August of 2011 that puzzled me. One of the two females appeared to be licking the back of the male’s abdomen (see image above). I am aware that male tree crickets produce glandular secretions from the thorax near the base of their wings, but I am not familiar with an analogous situation in katydids. However, I did find other references to this behavior (Fulton, 1933; Gwynne, 2001), likewise without explanation.

Mated females deposit their eggs single-file along a twig or the edge of a leaf, each ovum overlapping the last like shingles on a roof. The eggs are vulnerable to parasites, chiefly tiny wasps in the family Eupelmidae.

The nymphs that hatch feed generally on foliage, and molt four times before reaching adulthood. While it is difficult to identify most katydids in the nymphal stage, the robust body shape, relatively short hind legs, and mottled green appearance of Microcentrum nymphs helps them to be easily separated from other North American katydid genera.

Both large nymphs and adults can be preyed upon by a number of other animals, and especially by sphecid wasps like the Great Black Wasp. Adults can fly when pressed to do so, but generally creep about slowly so as not to draw attention to themselves in the first place.

Look for the Greater Angle-wing Katydid along forest edges, in gardens and yards, even in lone trees in open fields. They are also attracted to lights at night, though not in great numbers. The best way to find them is at night, with your ears and a good flashlight. Good luck.

Sources: Capinera, John L., Ralph D. Scott, and Thomas J. Walker. 2004. Field Guide to Grasshoppers, Katydids, and Crickets of the United States. Ithaca: Comstock Publishing Associates (Cornell University Press). 249 pp.
Elliott, Lang and Wil Hershberger. 2007. The Songs of Insects. Boston: Houghton Mifflin Company. 228 pp.
Fulton, B.B. 1933. “Stridulating Organs of Female Tettigoniidae (Orthoptera),” Entomol. News 44: 270-275
Gwynne, Darryl T. 2001. Katydids and Bush-Crickets: Reproductive Behavior and Evolution of the Tettigoniidae. Ithaca: Comstock Publishing Associates (Cornell University Press). 317 pp.

7 comments:

  1. I love Greater Anglewings! They are the most incredible leaf-mimics, and their tic-tic-tic songs are easily imitated with a pair of Latin percussion instruments called claves. They and the Oblong-winged Katydids were more abundant than usual in NE Ohio this past year.

    Thank you SO much for Orthoptera Thursdays, especially during these snow-covered February days.

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  2. I found one at my front door last night! It's really pretty :)

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    1. So happy for you, Nicole! I grew up in Portland, Oregon where we have *only* the Fork-tailed Bush Katydid. The katydids in the east are way more spectacular.

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  3. I caught what I believe to be a greater angle-wing just a few minutes ago, and I noticed that the insects eyes are red. Some pictures of this critter seem to have red eyes, and others seem to have green, is this sexual dimorphism? Or something else at play?

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    1. Zack, I honestly haven't paid that close attention to the eyes. Without seeing an image of *your* katydid, though, I can't know what species it is, or what gender it is.

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  4. If someone wants to find out what species and gender they have how would they show you a pic

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    1. You can click on the "forum" tab at the top of this page, and submit a question with an image, or link to an image.

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