by Carl Strang
Last week I made reference to Darryl T. Gwynne’s book on katydid mating system evolution. That book led me to other references, including a Ph.D. thesis by Marianne Feaver, who studied the behavioral ecology of three species of large meadow katydids (genus Orchelimum) under the direction of Richard Alexander at the University of Michigan in the 1970’s. I ordered a copy of Feaver’s thesis, and enjoyed reading it over the weekend. There was much richness of detail that will benefit my observations in the coming months and years. Here I’ll just share a few gleanings.
Feaver studied black-legged, common and gladiator meadow katydids. Maturation in the three species required 2 months from hatching to adulthood. In northeast Illinois the earliest species, O. gladiator, matures in late June, implying a late April hatch from eggs laid in the stems of plants.
Oviposition plants, food and cover are the three most important habitat features in these species. Upon reaching maturity, females move from nymphal areas that emphasize food and cover to places offering the best mix of food, cover and oviposition sites, and the males follow them there. The males then set up circular territories that space them out. These are defended mainly through song, though in high density populations physical combat often can take place. Defensive songs are characterized by increased number and rapidity of the tick portion of the song, the buzz portion apparently not important here. The territorial male reacts to the singing intruder, who may retreat or approach. In the latter case, after repeated warnings, the territory holder is likely to attack. The heavier male generally wins. Territory holding males tolerate silent males, which apparently are waiting for the territorial males either to be removed by predators or parasites, or to mate, after which they must retreat to gain back their weight.
They spend the night buried down in low, dense cover, then males begin spacing themselves out in mid-morning, and are singing by late morning. After territories stabilize, singing continues through the afternoon. Females assess and compare males, with mating taking place in the late afternoon. Females may take several days to choose a mate, however, and only mate once. In the early evening they break off to feed, then climb down into cover to spend the night.
This pattern provides a basis of comparison to other species, which will vary in detail. For instance, though I found a freshly mated female dusky-faced meadow katydid in the mid- to late afternoon, as I mentioned last week, that species reportedly does most of its singing at night.