10 August 2016

Bug noise is everywhere on hot summer nights. Some of the singers are tree crickets.

Tree crickets (subfamily Oecanthinae) live on every continent except Antarctica.  Camouflaged to match their habitat, these long, skinny, nocturnal insects live in trees and shrubs where they eat just about anything. They’re especially fond of aphids.

Male tree crickets “sing” to attract a mate by rubbing the ridges of their wings together, shown in the video below. (If there’s no sound when you play the video, click on the Play arrow in the black blob below the video.)

recording of tree cricket from Wikimedia Commons

The females don’t sing but they certainly listen.  Each species has a distinctive range of frequencies.  The ladies ignore the cacophony of other species. They only listen for their own. Click the arrow to hear the cricket.

Because insects are cold-blooded they move slower in cold and faster in heat, so they trill faster when the weather’s hot.  This means the frequency, and thus pitch, of their songs goes up in higher temperatures.  Here’s the sound of a snowy tree cricket (Oecanthus fultoni) at different temperatures.

So here’s an interesting problem:  Female tree crickets recognize their own species by the frequency of the trill, but the frequency increases as the temperature rises.  How do they recognize the higher-pitched songs?

In a study published last April, researchers at the University of Toronto Scarborough used laser Doppler vibrometry to measure vibrations inside the crickets’ ears.  The instruments were so sensitive that they could see changes at the cellular level.

The study found that “as the temperature changes, tree cricket ears adjust at a cellular and therefore mechanical level to match the changing frequency of the song.”

Read more about it here in Science Daily.

(video of a tree cricket “singing” in Alameda County, California from Wikimedia Commons)

7 Oecanthus species in western Pennsylvania as shown at Oecanthinae.com:  Four-spotted (O. quadripuntatus), Snowy (O. fultoni), Black horned (O. nigricornis), Pine (O. pini), Narrow winged (O. niveus), Two spotted (Neoxabea bipunctata), Davis’ (O. exclamationis)