Wild Side: Hitchhiking grasshoppers

Aided by human transport, these insects can create whole new populations.

Melanoplus differentialis on a chrysanthemum in a Vineyard garden center, fall 2017. — Matt Pelikan

My friend Margaret Curtin is a top-shelf naturalist. I closely follow her posts to the “citizen science” platform iNaturalist.org, where she helps me and many others identify plants and where I’m no longer surprised when she adds a new plant species to the Island flora. But a recent observation of hers nearly made me blow a gasket with amazement: a large grasshopper which either Margaret or iNaturalist’s artificial intelligence engine correctly pegged to the genus Schistocerca — a so-called bird grasshopper.

There are historical records, now more than a century old, of a population of Schistocerca alutacea around West Chop. (I cling to a dim hope that it persists, perhaps along the power line cut that traverses that section of the Island.) Mainland Massachusetts has a few recent records of Schistocerca lineata, closely related to alutacea, with observations across several years and the presence of immature individuals implying small, established populations. The American bird grasshopper, S. americana, occasionally wanders northward from its core range in the Southeast, and is possible as a vagrant in our area. And there is one Massachusetts record for S. obscura, another Southern species (more about that one later on).

But Margaret’s grasshopper was clearly none of the above. I ID’d it as S. nitens, the gray bird grasshopper, which ranges from roughly Nebraska south and west into Mexico and to the Pacific Ocean. My identification was promptly confirmed by my grasshopper guru. You can see why I was startled!

Looking more closely at the information Margaret uploaded to iNaturalist, I noticed that she found the grasshopper at one of the Island’s larger garden centers. I wasted little time getting over there, and while a diligent search did not turn up any bird grasshoppers, the mapped location in Margaret’s iNaturalist observation plus distinctive rocks showing in her photos allowed me to pinpoint the precise spot where the grasshopper had been sitting.

I looked up, checked what plants were close at hand, and read some of the information tags on those plants: a large, multispecies shipment of plants from the Monrovia nursery in Azusa, Calif. Mystery solved! Azusa, just east of Los Angeles, sits squarely in the range of Schistocerca nitens (though near an elevational limit for that grasshopper, as the land rises into the San Gabriel Mountains). The notion of a grasshopper hitchhiking across the continent was cemented by a comment from a California iNaturalist user, who described S. nitens as sometimes “very sedentary, hiding in a single plant for days.” (If you want to see how iNaturalist works, you can examine Margaret’s observation and the ensuing discussion here: inaturalist.org/observations/118517132.)

Such human-aided transport of Orthoptera turns out to be fairly common. Sometimes, the result is just a one-off record, a single individual that never turns up again. One example would be the Massachusetts record of Schistocerca obscura that I mentioned earlier. It turns out that grasshopper, which really has no business showing up north of the Mid-Atlantic states, was found in Winchester on a potted arborvitae at a garden center. 

Then there was a puzzling cluster of broad-tipped conehead (Neoconocephalus triops) records on the Vineyard last December and January. The species, a katydid of the southern U.S., is virtually inconceivable here as a natural arrival, especially in winter. But an individual found in Grafton County, N.H., proved to have arrived in a package of mustard greens. How they got outside remains a mystery, but the Vineyard records of this species probably likewise reflect refugees from the salad bowl.

Other times, hitchhikers can become established, creating new populations. The differential grasshopper, Melanoplus differentialis, is now well-established, at least around Thimble Farm. For many years, it was known on the Vineyard only from a single record from a farm in Chilmark. But a major influx arrived on chrysanthemums in September 2017, turning up in several garden centers as well as on plantings in Ocean Park, Oak Bluffs. That event apparently sufficed to create a permanent presence of this grasshopper on the Island.

These Orthoptera imports are all pretty benign, with the long-term results ranging from nothing at all to just another naturalized, fairly well-behaved member of our insect fauna. Other imports are less so. The winter moth, Operophtera brumata, non-native in North America, enthusiastically defoliates deciduous species, including oaks, maples, and blueberry in the spring. But the females of this moth are flightless: Either a bunch of females were accidentally imported here, or masses of eggs arrived, perhaps on imported shrubs. And the fearsomely invasive garlic mustard, Alliaria petiolata, went from absent to abundant here in the space of barely a decade, apparently spread largely in the form of seeds in compost or carried by vehicles.

When is an Island not an island? When it’s linked to the mainland by commerce. Realistically, this sometimes harmful ecological linkage is unlikely to change. People will continue to landscape, and in the absence of an adequate local supply, they’ll continue to import plant material. Food will continue to be shipped in. Vehicles will continue to transport whatever is stuck to them. But business as usual comes with hidden consequences.