The Mormon cricket: an insect with an identity crisis
In a meadow on National Forest land to the east of Filing 6, members of the Crystal Lakes Hiking Club came across a fat, green, flightless grasshopper a few years ago. I later identified it as a Mormon cricket, a kind of flightless katydid related to crickets and grasshoppers. The more I learn about this native insect the more I am thankful that Mormon crickets are harmless and solitary on our side of the Continental Divide. But they have a split personality and a bad reputation on the Western Slope, where they migrate in large bands with thousands of individuals driven by hunger and cannibalism, damaging crops and even causing dangerous road conditions!
General DescriptionA full-grown adult Mormon cricket can reach up to 2 or 3 inches long with a plump body and a “shield” that extends from the head back over the body, the origin of their group’s name, “shield-backed katydids”. The female (pictured below) has a long sword-like appendage at the end of her abdomen that is used to lay eggs in the soil. This ovipositor or “egg-putter” may look intimidating but is harmless to people.
Photo: A female Mormon cricket found with the Crystal Lakes Hiking Club, August 2018
Photo: Female Mormon cricket laying eggs in soil (Photo credit to Upupa4me on Flickr)
Life history and habitats Most Mormon crickets found east of the Continental Divide are green and solitary, eating flowering plants and shrubs in mountain meadows. Katydids, like all grasshoppers and crickets, go through incomplete metamorphosis, with young nymphs that look like smaller-sized adults until they reach full maturity over the course of 2 to 3 months.
The curious thing about these katydids is that on the Western Slope, on the other side of the Continental Divide, Mormon crickets look and behave very differently. From Montana to Nevada, including Western Colorado, Mormon crickets are darker colored and regularly come together in mass migration swarms in search of food, especially scarce protein and salts. The assumption is that the large bands of individuals provide protection from predators (mostly birds and rodents) through strength in numbers - predators are faced with so much food that they soon become full. Any one individual Mormon cricket in the swarm is at a lower risk of being eaten than an insect all alone in the prairie.
However, traveling as part of a swarm also has its drawbacks, including more competition for food and water. In the case of Mormon cricket swarms in the West, what begins as a group in search of food soon becomes a frantic march to escape cannibals. The Mormon crickets themselves are a rich source of protein and salt, so any individual that stops moving or is injured will be eaten by the other Mormon crickets coming up behind them in the swarm. This cannibal-driven death march can travel up to one mile a day for weeks at a time. Even though they don’t stop in any place for long, bands of Mormon crickets can destroy rangeland and cultivated fields as they pass through, especially small grains, wheat and alfalfa.
To add to their bad reputation, there are multiple reports of migratory bands of Mormon crickets causing dangerous, slick road conditions. Imagine a swarm of thousands of plump insects crossing a road and inevitably a few of them will be crushed by passing cars. As the cannibals reach the tasty road kill and enjoy their meal, more cars pass, more katydids die, more cannibals arrive…and you can imagine the results of this seemingly endless cycle on the road. Count this among the reasons to be thankful that our population of Mormon crickets tend to keep to themselves in mountain meadows. You can see a video of a recent migration crossing a road in Idaho HERE.
The mass migration behavior on the Western Slope also causes a complete role reversal in how Mormon crickets reproduce. In non-migratory populations and in many insects, the females choose a mate from among the males in her area, selecting the guy that presents the most promise of passing on strong survival traits to their young. But in the migrating swarms of hungry Mormon crickets, the males have the advantage because they present their mate with a packet of protein-rich nutrients as part of the deal, a delicious ‘nuptial gift’ that amounts to 30% of their body weight. They will not give this precious resource away to any hungry girl in the crowd, so in the case of the migrating swarms, the males have the privilege of selecting a female that is most worthy of their gift.
What's in a name? The common name ‘Mormon cricket’ comes from the history of Latter-day Saints settling in Utah in the 19th century. In 1848, a swarm of flightless katydids threatened to destroy the settlers’ second year of crops. A flock of seagulls arrived and saved the harvest by eating thousands of the insects, now remembered as the Miracle of the Gulls, commemorated with a monument in Salt Lake City and by the Utah state bird, the California gull.
See more insects of Crystal Lakes and Red Feather at the iNaturalist Project page and send any critter questions, comments or ideas for future columns to [email protected]
References Bailey, N.W., Gwynne, D.T. and Ritchie, M.G. 2005. Are solitary and gregarious Mormon crickets (Anabrus simplex, Orthoptera, Tettigoniidae) genetically distinct?. Heredity. 95(2):166-173. [link] Robson, L.J. and Gwynne, D.T. 2010. Measuring sexual selection on females in sex‐role‐reversed Mormon crickets (Anabrus simplex, Orthoptera: Tettigoniidae). Journal of evolutionary biology. 23(7):1528-1537. [link] Simpson, S.J., Sword, G.A., Lorch, P.D. and Couzin, I.D. 2006. Cannibal crickets on a forced march for protein and salt. Proceedings of the National Academy of Sciences. 103(11):4152-4156. [link] Sword, G.A., Lorch, P.D. and Gwynne, D.T. 2005. Migratory bands give crickets protection. Nature. 433(7027):703-703. [link] Tyus, H.M. and Minckley, W.L. 1988. Migrating Mormon crickets, Anabrus simplex (Orthoptera: Tettigoniidae), as food for stream fishes. The Great Basin Naturalist. 25-30. [link] “Miracle of the gulls”. Wikipedia, Wikimedia Foundation. Accessed on 27 Jan 2022. https://en.wikipedia.org/wiki/Miracle_of_the_gulls “Grasshoppers of Wyoming and the West”. University of Wyoming Department of Entomology. Accessed on 27 Jan 2022. http://www.uwyo.edu/entomology/grasshoppers/field-guide/ansi.html