Thursday, June 27, 2013

The Big-headed Grasshopper

It’s “OrThoptera Thursday” once again, and time for another grasshopper. My go-to place for grasshoppers here in Colorado Springs is a vast open space just up the street from my home. It is a shortgrass prairie in the literal sense in most spots, with extremely short, sparse turf in a mostly dusty, sandy, hilly plain that is dotted with scattered elm trees, sunflower, yucca, cacti, invasive weeds, and other low-growing herbs. This year it is even less lush.

Grasshoppers are usually abundant and diverse, but they are confined to only a few areas with herbs this year. Surprisingly, the dominant species I found yesterday was the Big-headed Grasshopper, Aulocara elliotti. It is technically one of the slant-faced grasshoppers, but it can easily be mistaken for one of the band-winged grasshoppers. It is easily identified by the very bright blue hind tibiae (“shin” segment on the hind leg), and large, rounded head.

I was still baffled initially, until I realized that last year I saw and photographed females, and what I was looking at yesterday were mostly males. One especially photogenic specimen, depicted here in the top- and bottom-most images, was also thermoregulating. Relying on camouflage and stillness is fine, unless the ground temperature is over 90° Fahrenheit like it was yesterday. Then you stand on tiptoe and even alternate which feet are in contact with the soil.

The Big-headed Grasshopper is fairly large as an adult, males ranging from 16-25 millimeters in length, females 22-35 millimeters. The species ranges across the entire western half of the U.S., north into the Prairie Provinces of Canada, and south well into central Mexico. While it prefers mostly shortgrass prairies and desert grasslands with sparse vegetation, I have encountered it at higher elevations (~8,500 feet) in coniferous woodlands. The adult insect can be found from June to September.

Nymphs emerge in mid-spring, having overwintered in the egg stage. They grow quickly, completing development to adulthood in 36-42 days. This may give them a head start in competing with other rangeland species. Males have only four instars (an instar is the period between molts), while females have five, so males mature sooner.

Aulocara elliotti feeds mostly on the green blades of grasses and sedges, but will also consume dry, cut grass, seeds, bran, and other ground litter it encounters while foraging. This species can occasionally reach pestiferous population levels and become damaging to crops and rangeland. Historical survey records show that it may reach densities of 20 specimens per square yard in mixedgrass prairie habitat, and up to 40 per square yard in desert grasslands. Not only does the feeding of the grasshoppers reduce available forage for livestock, but it can expose the soil to wind and water erosion.

The Big-headed Grasshopper is also capable of migrating, but apparently only for short distances. Observations in Arizona show that populations may move from one to seven miles in a season.

The continuing extreme drought in eastern Colorado would seem to guarantee that the Big-headed Grasshopper will continue to prosper while other species struggle. It will be interesting to follow the progress of this species in my neighborhood prairie patch.

Sources: Branson, David H. and Bethany Redlin (eds.). 2004. Grasshoppers: Their Biology, Identification, and Management (2nd Edition). US Department of Agriculture, Agricultural Research Service (PDF citation).
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.

3 comments:

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  2. Thank you for posting this. Those blue legs are really stunning!

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    1. You're welcome, thanks for the compliment!

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