Wednesday, February 10, 2021

Decoding katydids’ musical numbers

KatydidSome of us ride out the pandemic by basking in the pale glow of another Netflix binge. Insects play background roles in many of our favorite shows; therefore, my fellow couch surfers might be familiar with closed-caption terms like “insects trilling,” or “insects buzzing.”

While these phrases might capture the qualitative experience of arthropod auditory activities, they overlook the specificity of each message. Here in the Adirondacks, katydids are insects that can be heard producing tailor-made soundtracks through the summer into early fall. This article will describe the characteristics of katydids, explore the different types of songs produced by Adirondack katydids, and explain the impact these songs have on the local ecosystem.

About katydids

Katydids are insects in the family Tettigoniidae. They are close relatives of both grasshoppers and crickets, which are the groups of insects that comprise the order Orthoptera.  The term Orthoptera draws its roots from the Greek “ortho,” meaning straight, and “ptera,” meaning wing. Since all three insects communicate with sound, hearing is essential. It is performed using an eardrum-like flap called a tympanum, which is located on each of the hind legs for grasshoppers, and on each of the front legs for katydids and crickets. Katydids can be distinguished from crickets because they tend to have much longer hind legs than crickets. Unlike the brown and stocky crickets, katydids tend to be slender and green, with wings that look like leaves.

Adirondack species

Out of the 6,400 global species of katydids, 255 have been found in North America, and three have been confirmed in the Adirondack region: the common true katydid (Pterophylla camellifolia), the greater angle-wing katydid (Microcentrum rhombifolium, pictured), and the oblong-winged katydid (Amblycorypha oblongifolia). The common true katydid is nearly flightless. It hides in the canopy of deciduous trees, where it feeds on the leaves. This insect releases songs that use three pulses, exhibiting a “ka-ty-did” pattern. The sounds of its pulses are responsible for the name of the insect. The greater angle-wing katydid uses songs with a “tic tic tic” cadence. Oblong-winged katydids make an unusual rattling chirp noise, called an “itzic.” 

Musical insects

All male katydids and some females produce these sounds by rubbing their hind leg against one of their wings. This behavior is called stridulation, a word derived from the Latin phrase meaning “to make harsh sound.” Here in the Adirondacks, the greater angle-wing katydid is an example of a species with communicative males and females. In the true katydids and the oblong-winged katydids, the male stridulates and the female does not. Using this system, katydids produce and detect at least four kinds of songs, for the purposes of reproduction, territory demarcation, aggression, and defense. 

Reproduction songs

Reproduction songs are species-specific, in the sense that the tune is produced by males to capture the attention of conspecific females. Many katydid species can hear the song, but only females of the appropriate species will respond. This conversation occurs only during the mating season. Here in the Adirondacks, all of the katydid species mate in September and October. In warmer locations, mating may extend later into the fall. 

Territorial sounds

By comparison to the reproduction signals, territorial signals are meant for a wider audience. All three Adirondack katydids use these signals to repel other katydids, regardless of the species. Entomologists suggest that the signal reduces the number of fights, which can keep katydids from being injured. A stronger katydid may be able to project sound over a larger area, thus excluding competing males, and gaining access to more mates. With more mates comes the possibility to pass on more genes, perpetuating the most robust katydid genetics. All Adirondack katydid species exhibit this behavior. 

Aggressive signals

Aggressive signals are not meant to carve out territory, they are about trickery! Some Australian katydids mimic the sounds of male cicadas, to lure them into ambushes. The predatory katydids then eat the male cicada. Male cicadas are comparable in size to a katydid, but the katydid has chewing mouthparts, whereas the cicada has sucking mouthparts. Powerful mandibles give katydids the upper hand in these fights. Such behavior has not been documented in the Adirondack species of katydids, although cicadas and katydids coexist in this area. Adirondack katydids eat the leaves of deciduous trees, as well as grasses. 

It is debated if other male katydids will follow the sound of an aggressive signal. If so, they would initiate something akin to a feeding frenzy. Opponents of this idea suggest that katydids are too territorial to engage in such behavior. Supporters of the claim point out that katydids can detect the soundwaves, and if food is scarce, they might put their differences aside to hunt. 

In other encounters, the katydids are not the aggressor. For example, bats are nocturnal predators of many katydid species. They eavesdrop on the mating sounds of katydids to find them. In part because katydid wings are adapted to resemble foliage, they are not well-suited to rapid flight. Katydids interrupt their songs with tremulations, which are audible vibrations created by hitting the plant that they use for concealment. Tremulations mask the songs produced by katydids, confusing the bats. Hence, they are considered defensive songs. The bats that eat katydids also eat tomato-killing moths and in some cases mosquitoes, so hopefully they don’t fill up on katydids. Katydids are also preyed upon by birds, frogs, and spiders, but they use camouflage to avoid these predators, not tremulation. 

Katydids are excellent examples of insect communicators. With many different styles of song, they can exchange information about many topics, while minimizing the risk of leaving their secure habitat. When the snow melts and temperatures rise, maybe you too can hear katydids communicating in your Adirondack back yard. 

Pictured here: A greater angle-winged katydid Microcentrum rhombifolium Saussure (Orthoptera: Tettigoniidae), one of three species found in the ADK. 

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Shane Foye is an entomologist volunteering with the Cornell Cooperative Extension of Essex County Agriculture Program. Learn more about Shane and the on-farm projects he's working on at the CCE Essex Agriculture page: http://essex.cce.cornell.edu/agriculture/biocontrol-projects


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3 Responses

  1. Drew P Weiner says:

    Very interesting insect indeed

  2. Balian the Cat says:

    Growing up in the Hudson Valley I can recall listening to them on summer nights as we slept with the windows open. Don’t think I have ever heard one here in the north country.

  3. Noel A. Sherry says:

    Shane thanks for this very interesting article.
    I have heard these “songs” in Sep-Oct in the Adirondacks, on Twitchell Lake in Big Moose, and have always been fascinated by the late sounds of Fall there, in White Plains, NY, where I grew up, and now in Grafton, MA, where I live off seasons now. Katydids, Crickets, Locusts, etc. So these sounds take me right back to my youth and childhood, when these songs signaled late summer for me and a soon return to school. I did capture a few crickets in a jar to try to bring the songs in doors, and I think it worked. I often wondered what the songs “meant,” assuming they were very important for that species, and your piece addressed that for one or a few Adirondack species. So interesting. Again, thanks, for sharing your expertise in lay terms for all of us to understand and appreciate.
    Noel

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