Tree Cricket Courtship

Tree crickets, genus Oecanthus, are having quite the year here along the Colorado Front Range. Last month I went to Garden of the Gods park in Colorado Springs and could hardly go twenty feet without hearing a male tree cricket singing in the tall weeds or from a yucca blade. I even managed to capture videos of their singing and courtship.

Male tree cricket singing

There are five species of tree crickets in Colorado: the Prairie Tree Cricket, Oecanthus argentinus, Western Tree Cricket, O. californicus, Snowy Tree Cricket, O. fultoni, Black-horned Tree Cricket, O. nigricornis, and the Four-spotted Tree Cricket, O. quadripunctatus. Determining the species of a given individual is difficult to say the least because identification frequently hinges on the markings present (or absent) on the first two segments at the base of the antenna. I know! The whole insect is only about twenty millimeters maximum.

It is much easier to tell which gender is which. Females are very slender, with the front pair of wings hugging the body tightly. The short, stout ovipositor, used to insert eggs into berry canes and other plant stems, is easily visible.

Female tree cricket

Males on the other hand have the front wings greatly expanded into paddle-shaped musical instruments that make them look more like green lacewings than crickets. The intricate pattern of veins is all about lending support to the membrane that generates, amplifies, and projects the male's song. He lifts his wings into a heart shape at a 90-degree angle to his body in order to sing.

Tree cricket singing

The song is produced when a "scraper" on one wing is drawn across a "file" on the other wing, near where the wings join the thorax. The rapidity with which this happens cannot be captured by ordinary video cameras. Some male tree crickets align their wings with gaps in foliage, or even chew holes in leaves, to reduce acoustic interference and further intensify their call.

Singing male tree cricket with exposed metanotal gland in center of thorax

Like most crickets and other members of the order Orthoptera (grasshoppers, katydids, crickets), males have more than one kind of song. Once a male successfully lures a female, he switches to a softer song to help her orient to him. His raised front wings also expose a metanotal gland in the center of his thorax, which secretes a substance that the female feeds on. This is something of a distraction so that he can transfer a spermatophore, or "sperm packet" to her genital opening. The packet appears as a small, pearly blob near the tip of her abdomen in the video and images below.

Female tree cricket feeding from male's metanotal gland

The spermatophore takes time to drain sperm into her oviduct, and the female would undoubtedly eat it if she did not have the more attractive metanotal secretion to lick instead. She is sufficiently addicted that she feeds for several minutes after mating.

Tree crickets are omnivores, feeding on plants and small insects like aphids. Some species are truly arboreal, living in shrubs or high in trees, but a surprising diversity can be found in grassy fields, meadows, and similar habitats.

Male tree cricket at rest

There are many wonderful online resources to help you appreciate and identify tree crickets. One of the best is Singing Insects of North America, which covers grasshoppers, katydids, and cicadas along with crickets. Oecanthinae.com was created by Nancy Collins, a citizen scientist who has become a leading authority on tree crickets, even discovering a species new to science. Lisa Rainsong writes and illustrates the blog "Listening in Nature," which covers all kinds of acoustic phenomenon in the outdoors.

Male Prairie(?) Tree Cricket singing

Enjoy listening to, and looking for, tree crickets in your own neighborhood. Finding them is a challenge, but your patience will be rewarded. Above all, have fun.

Sources: Collins, Nancy. 2014. All About Tree Crickets. Parker, Colorado: Outskirts Press. 48 pp.
Dethier, Vincent G. 1992. Crickets and Katydids, Concerts and Solos. Cambridge, Massachusetts: Harvard University Press. 140 pp.
Elliott, Lang and Wil Hershberger. 2007. The Songs of Insects. Boston: Houghton Mifflin Company. 228 pp.

How Insects Sing

Observing the insect world requires one to use not just their vision, but their hearing, too. Many insects use sound to communicate with each other, or to ward-off enemies by startling them with a sudden, audible noise. How do insects make such a racket, anyway?

Male field cricket, Gryllus sp., Arizona

Stridulation

Most insects produce sound by rubbing one body part against another, a phenomenon known as "stridulation." The most accomplished stridulators are, of course, the members of the order Orthoptera. Most male grasshoppers, katydids, and crickets have modifications of the body that allow them to create, amplify, and broadcast auditory signals to attract mates and/or ward-off competing males.

Male larger meadow katydid, Orchelimum sp., singing in Nebraska

Short-horned grasshoppers in the family Acrididae rub special pegs on the inside surface of the hind femur ("thigh") against raised veins on the front wings while the insects are at rest. Slant-faced grasshoppers (subfamily Gomphicerinae) are especially accomplished at this and their soft zip-zip-zip songs are easily heard during daylight hours. Below is a video of a male Psoloessa grasshopper stridulating vigorously. Unfortunately, the incessant prairie winds on the eastern Colorado plains overwhelm the 'hopper's song.

Male Psoloessa sp. grasshopper stridulating

Band-winged grasshoppers (subfamily Oedipodinae) also stridulate, but not as loudly. You are more apt to see two males sizing each other up instead of a male courting a female. In the video below, two male Carolina Grasshoppers stridulate aggressively, side-by-side, until the loser leaves the stage.

Male Carolina Grasshoppers, Dissosteira carolina, stridulating aggressively

Katydids and crickets are the most accomplished of all stridulating insects, in part because the wings of the male insect are highly modified to produce sound; and the insect often stations itself in a circumstance that enhances the projection of sound, such as the mouth of a burrow, or between leaves.

Male tree cricket, Oecanthus sp., singing, Colorado

Male tree cricket at rest

Most male katydids are "left-handed," meaning that the left forewing overlaps the right forewingwing. Contrastingly, most male crickets are "right-handed." In both cases, the edge of one wing is equipped with a "file" of fine teeth, while the other wing has a bladelike "scraper" that is drawn rapidly over the file to create the song.

Singing male field cricket, Gryllus sp., Colorado

The songs we hear most often are "calling songs" designed to attract females; but, crickets in particular produce two other types of songs: a "rivalry song" that is directed at another male during and/or after a confrontation, and a soft "courtship song" to entice a female into mating.

Male Drumming Katydid, Meconema thalassinum, Ohio

Percussion

A surprising variety of insects, from treehoppers to stoneflies, to beetles actually smack body parts against a substrate such as a leaf or twig to generate vibrations that are received by potential mates. Sometimes these body-slamming signals are also audible. The Drumming Katydid, Meconema thalassinum, and "wing-tapper" cicadas in the genus Platypedia do not produce sound the way most other members of their clan do. Instead, they strike a blow against a branch, leaf, or twig to call to the opposite sex. This is still audible to us, too.

Wing-tapper cicada, Platypedia putnami, Colorado

Males of most cicada species have a pair of built-in percussion instruments. Large pits take up most of the volume of the abdomen and are covered by "lids" called opercula (singular: operculum). Inside each chamber, a strong muscle pulls and releases another organ called a tymbal. The tymbal buckles under the muscle's tug, generating a noise, then snaps back when the muscle relaxes, making another noise. The muscle twitches at such a high rate that we hear one continuous sound, and a very loud one at that.

Underside of male Tibicen sp. cicada showing operculum

Hearing

How do the insects hear each other? Insects do not have ears, per se, but they do have auditory receptors called typmana located in peculiar places. Short-horned grasshoppers have an opening on each side of the abdomen, near the base. Cidadas likewise have their typana located in the front section of the abdomen. Katydids and crickets have a slit located on the front surface of the tibia ("shin") on each front leg. The tympana is usually represented as a thin, oval membrane located inside the "ear" opening.

Greater Anglewing Katydid, Microcentrum rhombifolium, showing "ear"

Resources

Many singing insects can be identified reliably only by differences in their songs, so it helps to familiarize yourself with their calls. Thankfully, a variety of resources are available to do just that. The "Singing Insects of North America" website is particularly useful. Examples of songs are available as audio files for most species.

Male conehead katydid, Neoconocephalus ensiger, singing, Massachusetts

Lisa Rainsong's superb scientific blog "Listening in Nature" covers bird songs, frog choruses, and other sounds of nature as well as insect songs.

Several books exist that address insect songs, but my two favorites are The Songs of Insects by Lang Elliott and Wil Hershberger (2007, Houghton Mifflin Company), and Crickets and Katydids, Concerts and Solos, by Vincent G. Dethier (1992, Harvard University Press).

You should be hearing field crickets any time now, if you aren't already, along with the daytime calls of some acridid grasshoppers. Enjoy the symphony.

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.

OrThoptera Thursday: California Angle-wing Katydid

In previous weeks I have written about the Greater Angle-wing Katydid and the Lesser Angle-wing Katydid, but there are four other species in the U.S. One of these, Microcentrum californicum, is found commonly in Arizona, and the length of California west of the Sierras.

The California Angle-wing Katydid is the smallest member of its genus, adults ranging from 41-52 millimeters. Note that the male has a brown stridulation area (its “shoulders”) like the Lesser Angle-wing, but its geographic range leaves no room for confusion.

The specimen shown here was attracted to a blacklight set up in Peppersauce Canyon in the Catalina Mountains of Pima County, Arizona on September 2, 2011. There was also a female Greater Angle-wing found in the same location on the same night.

The remaining Microcentrum species include M. louisianum, the Louisiania Angle-wing, found from Louisiana and Mississippi north through parts of Arkansas and Tennessee to the bootheel of Missouri. Microcentrum minus, the Texas Angle-wing, is found only in extreme south Texas; and the Southwestern Angle-wing, M. latifrons, is recorded from the Big Bend area of Texas and the southeast corner of Arizona.

>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.
Eades, David C., Daniel Otte, Maria Marta Cigliano, and Holger Braun. 2013. Orthoptera Species File Online. Version 5.0/5.0
Walker, Thomas J. and Thomas E. Moore. 2013. Singing Insects of North America. University of Florida.

OrThoptera Thursday: Lesser Angle-wing Katydid

Last week I wrote about the Greater Angle-wing Katydid, a common species over much of the U.S. While reviewing images for that post, I discovered I also had images of its cousin, the Lesser Angle-wing Katydid, Microcentrum retinerve, from the same location in south-central Ohio.

The Lesser Angle-wing, as its name suggests, is a smaller animal, adults ranging from 44-53 millimeters in length compared to the 52-63 millimeter Greater Angle-wing. Males of Microcentrum retinerve have the stridulatory area consistently brown in color, a sharp contrast to the bright green of the rest of the insect. I also find that Lesser Angle-wing Katydids have the veins of the front wing more explicitly defined than in the Greater Angle-wing, making the creature even more convincing as a leaf mimic. This rougher texture is not always a defining character, but it helps.

The key character in separating these two species of Microcentrum would naturally be the most difficult to capture from images of wild, living specimens. The front edge of the pronotum (top of thorax) is smooth and straight in M. retinerve. This front margin has a very small, central tooth in M. rhombifolium.

Both species occupy the same kind of deciduous forest habitat, but the Lesser Angle-wing Katydid has a more restricted range. It occurs from Long Island and New Jersey south to northern Florida and west to Missouri and extreme east Texas and Oklahoma.

Locating a singing male can be highly frustrating, as the interval between songs is even longer than in the Greater Angle-wing; and they don’t have a “courtship song” of repeated tics. Each call is a rapid series of 3-5 pulses, too fast to count (but revealed visually in sonagrams), repeated about once per second for a short period.

Look for the adults at the tips of branches on trees at night. It is actually easier to see them in a flashlight beam than during the day because they are more active, and stand out vertically against the otherwise horizontal plane of foliage. Moving katydids are always easier to spot than stationary ones.

The Lesser Angle-wing Katydid will also fly to lights at night, which is how I obtained these few images. I am still not absolutely certain that the female is not actually a Greater Angle-wing specimen. It was climbing high on the wall and windows of a building and I could not gauge its size accurately, let alone note whether there was a tooth on the front edge of the pronotum.

Adults are most commonly encountered between late July and mid-October, but depending on latitude they may reach maturity as early as May. Other facets of behavior and life cycle are essentially identical to those of the Greater Angle-wing Katydid.

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.