|26 s video [51.1MB] of caged male calling, made by Nancy Collins, used by permission.|
|15 s of calling song [1.07MB]; male from Bentsen-Rio Grande Valley State Park, Hidalgo Co., Texas; 23.2°C. (WTL575-3-b)|
Spectrogram of 5 s of calling at 23.2°C (from WTL575-3-b). Dominant frequency 2.3 kHz.
Click on spectrogram to hear graphed song.
Spectrogram of 1 s of calling, featuring the middle chirp of the song graphed above.
Click on spectrogram to hear the chirp played at 1/8 speed (and at 1/8 its dominant frequency).
Identification: Length–16 mm. No other U. S. cricket produces uniformly spaced chirps at a rate of less than one chirp per second. Antennal markings similar to those in the photograph above.
Habitat: Disturbed areas of mixed growth forms.
Season: The only records are from May and June, but there are no negative data for other months.
Song at 25°C: A highly regular, slow, continuous series of long, melodious chirps. As shown in the spectrograms above, each chirp usually begins with a pair of pulses that is followed by a series of pulse triplets. Most chirps total 20 or 23 pulses.
Song data: See Walker & Collins (2010) and spreadsheet.
Similar species: Two other species of the Oecanthus rileyi species group, fultoni and rileyi, occur in the U.S. but each calls at chirp rates several times as fast as alexanderi and neither occurs in south-most Texas.
Remarks: Nancy Collins, a nurse in Racine, Wisconsin, developed an interest in Oecanthinae in the summer of 2006 and soon pursued that interest with vigor and to good effect. For example, she founded a Tree Cricket Appreciation Group on Facebook (currently with 17 members) and authored a well-illustrated web site on the subfamily. In May 2009, she organized a field trip to find two species of Oecanthinae known in the United States only from the lower Rio Grande valley and not collected there for more than 50 years. She failed to find either of the two target species, but recorded an unfamiliar tree cricket call in two counties and heard it in a third. The song proved to be the same as one that R. D. Alexander had recorded in three localities in Mexico in 1965. This led to the description of this species, which is named in honor of a pioneer in the study of crickets and katydids and the first person to record its distinctive song.
This species and the other species in the Oecanthus rileyi group have justifiably been dubbed "thermometer crickets." They produce chirps at rates that are so uniform and so linearly dependent on temperature that the approximate temperature where a male is calling can be deduced from its chirp rate as easily measured in the field. For more, see Walker & Collins (2010).
More information: genus Oecanthus, subfamily Oecanthinae.
References: Walker & Collins 2010.
Nomenclature: OSF (Orthoptera Species File Online)