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How, when, and why do they sing?
Where are their ears?

How do they make their songs?

The questions "how" and "when" are intertwined. Crickets and katydids are rather like annual plants. They live until a freeze kills them, but their eggs are already laid in plants or soil and will overwinter in that state. Spring Field Crickets overwinter as nymphs and mature in late spring which is why we hear them in late May instead of July.

 

When the eggs hatch, the nymphs (immatures) do not have wings. They go through multiple molts as they grow, eventually developing tiny “wing buds.” Males become the singers, but they’re not able to sing until their final molt into full-sized wings. (Female katydids don’t sing, but they may make short “tics” that are signals to the males.)

Clockwise from top left: tree cricket nymph, Spotted Ground Cricket nymph, Rattler Round-winged Katydid nymph, Short-winged Meadow Katydid nymph.
How do they sing once their wings are full-sized?

Cricket and katydid instruments, or stridulatory areas, are located at the base of their upper set of wings (the tegmina).  One wing has a file at its base and the other has a scraper. (There is a beautiful macro photo in the Songs of Insects here.) They move their wings across each other at a very high rate of speed and do so either continuously or in short bursts, creating either long, steady trills or a rhythmic pattern of shorter songs. Katydid wings are left over right, as in the Gladiator Meadow Katydids below, and cricket wings are right over left. 

My Listening in Nature blog post called “Instruments and Performance Techniques: How Crickets and Katydids Make Their Songs” goes into greater detail with more illustration. Click on the highlighted text above to see and hear the descriptions, as I can add more recordings there.

How do they hear?

If you want to find their ears (tympana), look at what would be the elbows on a human! They can move their ears independently as a result. It's easier to see the tympana on one of the larger katydids, but they're visible even on tree crickets.

Top left: a Curve-tailed Bush Katydid "ear."

Right: the ears, or tympana, on this Texas Bush Katydid are easily visible if you look just below the "elbows."

Bottom left: The tympana on this tree cricket are harder to spot, but I think you can find them if you check the same location.

When do they sing?

Singing insect species mature at different times. A few are early, singing in June into July, but the majority begin their season of song anywhere from mid-July to mid-August. The earliest singers drop off by late July or early August, but by then the majority of species will be singing in a triumphant orchestral tutti. A robust ensemble continues through August, with some species fading away in early September and many others finishing their season a few weeks later either due to old age or a hard frost. The most resilient may continue into early October, especially along Lake Erie.

There is a separate page in this field guide with an approximate singing calendar for many of these insects. Just keep in mind that the dates will be a little earlier if the weather has been hot or later if it’s been a cool spring and summer. Also, singing insects will mature a little earlier farther south of Lake Erie but persist longer into the fall close to the lake.

Why do they sing?

It’s for the females, who may or may not answer with a brief “tic” or “tsip” call. Some males also have specific song patterns that are warnings or challenges to other males.