The word katydid is fairly new to English, and can boast two other unique features: it is onomatopoetic and it is wholly American. The American katydid was first described systematically by the great self-taught American botanist John Bartram in 1784. The word did already exist in a different form, that some say is closer to the sound of the insect: catedidist. This form can be found as early as 1751, but as botanist to King George the Third and both colleague of and supplier to Carl Linneaus, Bartram’s spelling prevailed. The katydid closely resembles the grasshopper but is in fact more closely related to crickets. Final fun fact: during mating, the male katydid presents the female katydid with a spermatophylax (no need to give the etymology of this word, the first half tells you all you need to know), a gelatinous mass that the female eats, presumably to aid in her survival.
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