One question that I keep coming back to is, “Why are rare species rare?” This query often inspires a related one: “If it’s rare now, was it always rare?” I never expect simple answers, especially not simple answers that apply to all rare species. But rarity can be a revealing frame to look through.
An example I’m currently puzzling over is the autumn yellow-winged grasshopper, Arphia xanthoptera, a magnificent insect that appears to be about as rare in New England as a resident species can be. A robust grasshopper about two inches long, this species is hard to miss where it occurs. It flies powerfully, showing bright yellow hindwings while doing so, and it crepitates loudly in flight, smacking its forewings together to produce a distinctive rattle.
In the case of this A. xanthoptera, my second question is easily answered: No, it has not always been rare. Waxing poetic in a 1920 publication about both the grasshopper and its preferred habitat of little bluestem grassland, the entomologist Albert Morse described A. xanthoptera as common across southern New England, even citing records from Nantucket (though not Martha’s Vineyard). Historical records in the Global Biodiversity Information Facility’s database support this assessment –– though, oddly, the robust string of Massachusetts records declined abruptly in the 1930s.
And today? This grasshopper occurs patchily but broadly from Maryland west to the tallgrass prairies of Iowa, south almost to the Gulf of Mexico. But the broad New England distribution of a century ago appears to have withered to one known location in New England, at a Land Bank property near my home in Oak Bluffs. The nearest records to Oak Bluffs in the iNaturalist platform are from the outskirts of Baltimore, Md.
iNaturalist includes 3,905 Massachusetts records for Oedipodinae, the subfamily to which A. xanthopera belongs. Of those, only three (all from Oak Bluffs) reflect this species, making it by this measure the rarest band-winged grasshopper known to be resident in the state. To be sure, this species is wary and hard to document. But as I noted, it is also conspicuous, and many other commonly recorded grasshoppers are nearly as wary. If A. xanthoptera were out there, people would be documenting it.
This striking decline is all the more puzzling given the habits of this grasshopper. Bluestem-rich grassland, on the Vineyard and indeed on the nearby mainland, is hardly a scarce habitat type. And Arphia xanthoptera routinely flies scores of yards and reaches heights of 30 feet or more when disturbed; if it wanted to, it could easily travel for miles in just a few days to colonize new areas. So what could account for its regional collapse?
I have no certain explanation. But it is far from the only grasshopper that has declined in numbers and distribution in our region since Albert Morse’s time. Very likely, the wane of agriculture and the ensuing process of reforestation in New England is part of the picture. The Orthopteran fauna that Morse enjoyed had grown far beyond its aboriginal scale, benefiting from the extensive clearing of farm fields and pasture. And the reverse of that process has steadily reduced the habitat available to grasshoppers, including A. xanthoptera.
But many grasshoppers remain abundant despite these changes, so there must be some characteristic of A. xanthoptera that makes it especially vulnerable to the loss and fragmentation of its preferred habitat. Perhaps it requires habitat with some set of very specific features: soil structure, ratio of little bluestem to other plants, a minimum size? But if the species is so fussy, how could it have been so widespread in the not-too-distant past? And how does it remain reasonably common in other parts of the U.S.?
A related but subtly different notion seems more likely to me. Instead of attachment to some very specific habitat type, perhaps this grasshopper (or at least its southern New England population) evolved an aversion to unsuitable habitat, making it unwilling to disperse away from a congenial setting. There could be advantages to this, if that preferred setting were extensive or enduring: Why leave behind a meadow full of potential mates to go explore unknown territory? Your chances of reproducing successfully are much greater if you stay at home.
But the evolution of this behavioral trait would have required early successional, bluestem-rich habitat to have existed in large tracts, persistent examples, or both. Such conditions sound very much like the type of anthropogenic sandplain grassland many ecologists believe was widespread in coastal parts of our region, created by Native American land management and agriculture and then maintained by the land clearing, farming, and grazing practices of European settlers.
So, I suspect, a tendency that was advantageous long ago became maladaptive amid 20th-century ecological change. Is this explanation certain? Oh, heavens no! All I really know about Arphia xanthoptera is that it likes little bluestem, it went quickly from common to rare, and it seems curiously unwilling to use its powerful flight to disperse across the landscape.
But those patterns are unmistakable, and I can think of no other way to explain them. I suspect that the boom and bust of Arphia xanthoptera in southern New England bears the marks of the distant ecological history of our region.
