Oecanthus

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Grasshoppers & Allies Supplemental: Tree Crickets (Oecanthus)
© W.P. Armstrong 15 April 2009
Tree crickets belong to the genus Oecanthus in the family Gryllidae. Unlike the large black crickets that occasionally enter houses, these are small brownish or greenish crickets only 13 mm long (1/2 inch) that live among the leaves of trees and shrubs. On warm summer evenings in southern California, they make the familiar chirping sound that fills the night air, as males rub their wings together to attract females. The "song" is produced by frictional movements of roughened veins at the bases of the forewings. Each species has its own characteristic song. The song of O. fultoni and O. rileyi consists of a pulsed, high pitched "treet-treet-treet," while the song of O. californicus and O. argentinus is a continuous trill. The male featured in the following images is one of the latter two species. The audible volume produced by such small insect is remarkable. In fact, it is very difficult to spot the male making this loud sound even when you are standing near its shrub with a flashlight. Like many other animals, the chirping is a prelude to courtship and mating.

Introduction

When most people think of crickets, they are probably referring to the large, black or brown crickets that often enter houses in southern California. This includes the introduced European house cricket (Acheta domesticus) and field crickets of the genus Gryllus. The latter crickets live on the ground in cracks and crevices, and under litter, vegetation and stones. Although they make loud chirping sounds in spring and early summer, they are very different from smaller tree crickets that produce the predominant sounds on warm summer nights. Field crickets can be a nuisance in your home with their annoying, incessant chirping, especially when you are trying to sleep. Like master ventriloquists, it is difficult to locate their origin. They are usually in very inaccessible locations, such as under furniture or appliances. Their presence in the home is considered an omen of good fortune in many parts of the world, and in China they are kept in captivity. Since they are omnivorous, they may nibble and on a variety of foods, including food-stained clothing. They are also fond of beverages, including beer.

Female field cricket, possibly (Gryllus pennsylvanicus). Note the long ovipositor.


Tree Crickets of the Genus Oecanthus

The following information about tree crickets of the genus Oecanthus is summarized in the outstanding book by Charles L. Hogue entitled Insects of the Los Angeles Basin (1993). Sound in the males is produced by stridulation: The basal edge of one forewing (scraper) is rubbed along a filelike ridge (file) on the ventral side of the other forewing. Both forewings possess a file and scraper. The file is actually an enlarged, roughened vein with numerous transverse ribs. Two vertical files are visible in the above image, one at the base of each forewing. The sound produced is surprisingly loud considering the small size of this insect. This is similar to a wooden cricket which is played by rubbing its toothed underside (file) with a small, wooden mallet or scraper (wooden cricket). Other members of the Orthoptera, including long-horned grasshoppers and katydids (Tettigoniidae) also produce sound by the file and scraper method.

According to Hogue (1993), the chirp rate varies with changes in the surrounding (ambient) air temperature, increasing at higher temperatures and decreasing at lower temperatures. The snowy tree cricket (O. fultoni), also called the "thermometer cricket," indicates the temperature in degrees Fahrenheit if one counts the number of chirps in 13 seconds and adds 40. For example, at a temperature of 78 degrees there would be 38 chirps in 13 seconds. Oecanthus rileyi chirps about twice as fast as O. fultoni at the same temperature. The species shown in the following images on this page had a continuous trill, so I was unable to calculate the temperature. I had to resort to a mercury analog thermometer. Incidentally, the temperature was 78 degrees Fahrenheit (25 degrees C) at 10:00 P.M. Pacific Daylight Time in San Marcos, California (27 August 2007).

Snowy tree cricket (Oecanthus fultoni): Male (left) has broad wings. Female (right) has narrower wings and slender ovipositor. Both insects collected by the author in Big Rock Creek (Los Angeles County) in 1964. At the time of this photograph, the specimens were 43 years old.

According to Capinera, Scott and Walker (2004), several additional species of Oecanthus occur in southern California, including O. californicus (western tree cricket), O. argentinus (prairie tree cricket) and O. quadripunctatus (4-spotted tree cricket). These three species all have continuous trills with pulse rates of 40-57 per second (depending on the species) at 77 degrees Fahrenheit. They can be differentiated by markings on the first and second antennal segments. According to Hogue (1993), the most common species in the Los Angeles Basin is O. argentinus.

According to Dr. Thomas J. Walker, Department of Entomology & Nematology, University of Florida (personal communication, 2007), the species shown below is the western tree cricket (Oecanthus californicus). This species has a continuous trill with pulse rates of 57 per second at 25 degrees Celsius.

As in many other animal species, singing is a prelude to courtship and mating; however, Oecanthus species have an especially interesting sexual behavior. It is described by Fulton (1915) in the following paragraph:

    "While the male is vigorously singing, the female lingers near and repeatedly nudges him, until finally the male ceases his song and holds his wings in a raised position; thereupon, the female promptly climbs on top of the male. In this position, she eats from the metanotal gland just behind the wings of the male (from whence an alluring substance is secreted). The insects are then in a situation proper for mating, which takes place with the female on top of the male."

The images of Oecanthus on this page were taken with a Sony T-9 digital camera in the dark using the built-in flash. I held a flashlight in my left hand and the Sony T-9 in my right, with my arms extended over the shrub. Illumination from the flashlight allowed the camera to spot focus on the subject. The flash adjustment was automatic. Only minor tweaking of these images was done with Photoshop.

A male tree cricket (Oecanthus californicus) sitting on the leaf of Arbutus unedo.

A male tree cricket (Oecanthus californicus). Males have a flattened body and broad wings. Females are cylindrical with wings folded around the body.

A male tree cricket (Oecanthus californicus) in the chirping mode with the wings raised above the abdomen.

A male tree cricket (Oecanthus californicus) in the chirping mode with the wings raised above the abdomen.

A male tree cricket (Oecanthus californicus) in the chirping mode with the wings raised above the abdomen. Sound is produced by stridulation: The basal edge of one forewing (scraper) is rubbed along a filelike ridge (file) on the ventral side of the other forewing. Both forewings possess a file and scraper. The file is actually an enlarged, roughened vein with numerous transverse ribs. Two vertical files are visible in the above image, one at the base of each forewing. The sound produced is surprisingly loud considering the small size of this insect. This is similar to a wooden cricket that is played by rubbing its toothed underside (file) with a small, wooden mallet or scraper (see next image). Other members of the Orthoptera, including long-horned grasshoppers and katydids (Tettigoniidae) also produce sound by the file and sraper method.

The following website called "Singing Crickets of North America" by Thomas J. Walker and Thomas E. Moore contains a lot more information about crickets, including recorded songs and images. In fact, one page of this fascinating website has recorded songs of the snowy tree cricket (Oecanthus fultoni). Go to the following URL and click on the first song of this insect. The individuable chirps can easily be heard compared with the recorded tree cricket song on this page: Click Here

A wooden cricket imported from Thailand.  It is played by rubbing  
its toothed underside (file) with the slender, wooden mallet (scraper).

References:

  1. Block, B.C. 1966. "The Relation of Temperature to the Chirp-Rate of Male Snowy Tree Crickets, Oecanthus fultoni (Orthoptera: Gryllidae)." Annals of the Entomological Society of America 59: 56-59.

  2. Capinera, J.L., Scott, R.D., and T.J. Walker. 2004. Field Guide To Grasshoppers, Katydids, and Crickets of the United States. Cornell University Press, Ithaca, New York.

  3. Evans, A.V. 2007. Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc. New York, New York.

  4. Fulton, B.B. 1915. "The Tree Crickets of New York: Life History and Bionomics." New York Agricultural Experiment Station Technical Bulletin 42: 56-59.

  5. Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County.

  6. Walker. T.J. and T. E. Moore. 2006. "Singing Insects of North America." Available at: http://buzz.ifas.ufl.edu/. Accessed 1 September 2007.

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