Last week we escaped the chilly confines of Maryland’s winter and visited the tropical rainforest of Costa Rica to meet otherworldly whip spiders as they stalked their victims along muddy jungle trails. This week we turn our eyes upward to discover a true master of disguise, the amazing round-headed katydid, a.k.a false katydid or bush-cricket. Katydids are masters of disguise. If you look carefully at their wings, you will notice how closely the delicate network of veins resembles veins of a leaf. This deception and their green coloration surely help them avoid detection by birds, reptiles, and other hungry predators that would find them a tasty treat. Round-headed katydids are found not only in tropical rainforests of Central America but also in North America where one common species, the oblong-winged katydid, is a common denizen of landscapes from Texas to Vermont. While green is the most common color form of round-headed katydids, some species sport glorious color morphs in shaded of yellow, brown, and pink.
Like other members of the Orthoptera clan such as crickets we met in previous episodes, katydids produce sound with their forewings. One wing bears a structure called the scraper, which is pulled across a complementary structure called the file on the other forewing. The resultant vibrations produce a wonderful song with which the six-legged troubadour woos his mate. The female katydid hears the song of the male through small openings, ears if you like, on her front legs. The sound enters through the slits and is amplified in a hornlike chamber within the leg. A membrane inside acts much like our eardrum and captures the sound. Sensory cells attached to the membrane pickup these vibrations and the female katydid’s tiny brain decides if he’s giving her good vibrations or not.
Along the rainforest trail at night, one can sometimes catch a glimpse of a katydid that might go undetected in the light of day.
A fascinating study determined that larger bush-crickets, close relatives of our round-headed katydid, were more successful in attracting babes than smaller males. Here is the reason why. In addition to good vibrations, males of many species of katydids give their mate another type of gift, a nuptial gift called a spermatophylax. The spermatophylax is a protein-rich bundle of food that accompanies a packet of sperm during mating. Like all little sperm, the ones in this packet fertilize dozens of eggs within the female katydid. After the sperm have entered her body, the female consumes the nutritious protein packet, her nuptial gift. By providing the she katydid with dinner and a date, the male enables her to produce more or larger eggs, thereby ensuring the birth of more of his own vigorous youngsters. As you might guess, larger males with louder songs provide larger nuptial gifts, hence the female’s preference for big guys with deep, loud courtship songs. Even in the world of small creatures like katydids, size matters!
Bug of the Week gives special thanks to Carlos and the other nocturnal adventurers at Aguila de Osa who were the inspiration for this episode. The fascinating article “Bushcricket song as a clue for spermatophore size?” by Gerlind U. C. Lehmann and Arne W. Lehmann, and “The Insects” by P. J. Gullan and P. S. Cranston were used as references for this episode.