Naturalists can’t be sissies — even when it involves stinkiness, decay, and greenhead flies.
Of all the habitats found on the Vineyard, the one I know least well is likely salt marsh. For one thing, we don’t have much of it, certainly not the vast expanses of it one finds in some other places on the Massachusetts coast. For another thing, the marsh we do have is not generally easy to get onto. And finally, a salt marsh in summer is shadeless, wet, reeking of decay and microbial action, and often a tangle of greenhead flies and mosquitoes.
But naturalists can’t be sissies about this kind of stuff. So one of my projects this summer was some long-overdue exploration of salt marsh, which as an ecological system is wildly productive, utterly fascinating, and important for processes ranging from fish reproduction to sequestering excess nitrogen.
A healthy salt marsh offers great opportunities to wildlife, but with the drawbacks of high salinity and unpredictable flooding. With such a rich resource to exploit, though, a wealth of insects have found ways to flourish on this dynamic boundary between land and sea.
Take, for example, the salt marsh meadow katydid, Conocephalus spartinae. A half-inch long in the body, with whip-like antennae and elongated hind legs, this insect seems to spend all its time on salt marsh, and I don’t mean at the upper edge — the highest densities I found were in the tallest, most lush patches of Spartina marsh grass, in wet areas of the marsh.
As with other katydids, the females of this species have menacing but harmless organs called ovipositors extending from their abdomens — devices for egg-laying, and the size and precise shaping of these organs suggests that they’re designed for very specific jobs. Eggs are laid during the late summer, when adults are active; they hatch on an irregular schedule the following season, and the hatchlings pass through a series of molts as they grow to maturity.
The salt marsh katydid, found on the East and Gulf Coasts from Texas to Maine, comes in two color variants, or “morphs” — brown and green, present in about equal numbers in our population. Multiple morphs are not unusual among katydids and grasshoppers, and since a katydid’s body color mainly needs to serve as camouflage from predators, having brown and green morphs may be a way for a species to hedge its bets on the condition of vegetation.
Falling into the water is easy to do on a salt marsh (why, I managed it myself). But it’s a serious blunder for
most tiny air-breathing animals. Several salt marsh katydids missed their aim while jumping (if they aim at all) and landed squarely in the drink as I followed them with binoculars. They seemed unperturbed, spreading their front four legs for buoyancy and motoring efficiently to shore, powered by kicking hind legs. No doubt most insects have instincts that allow them to “swim.” But the aplomb which these katydids do it seemed notable, and I bet a strong boating instinct is one behavioral adaptation this species evolved as it took to the marsh.The salt marsh Conocephalus, though small, is actually one of the larger insects on the marsh, and it is also plentiful in the right kind of habitat. These factors inevitably add up to significant ecological importance, at least locally. Simply put, a lot of katydids equal a lot of eating, and the impact on plant populations is magnified by the fact that katydids feed largely on seeds and flowers, not just leaves. (They also happily dine on smaller insects.) Amazingly, the ecological effects of insect grazing on a New England salt marsh have been studied! An elegant 1987 article in the journal Oecologia documents the “intense flower and seed predation” that make Conocephalus a “potent selective force” on salt marsh perennials. This little bug helps shape the marsh!
How do salt marsh katydids handle flooding? To avoid daily high tides, I’m sure they simply move higher on the marsh — or even just higher up on the vegetation. The real trick is how a population of these insects survives storm-related flooding, a real possibility during this katydid’s late-summer reproductive period. Tropical storm surges may last for hours or days, and wash well above the normal boundary of the marsh.
Can adult katydids survive an event like that? Perhaps they hang on and hold their breaths, but I imagine a major storm tide kills or washes away a high percentage of katydid nymphs and adults. But here’s another guess: The fate of the adults doesn’t really matter, because the species has put its ingenuity into preserving its eggs instead.
I bet they lay eggs in a very specific place — remember that specialized ovipositor? — that keeps the eggs from washing away. Perhaps they put their eggs underground into the root system of marsh grass, counting on the fibrous mat of roots to hold everything in place through the flood (after all, roots are what stabilize a marsh). However they lay eggs, though, I bet it’s the secret to the persistence of this species, and I’d sure love to watch them do it. Maybe next summer!