Wild Side: Survivors

Red-legged grasshoppers can be found well into December.

A female red-legged grasshopper hangs on to life in an Oak Bluffs yard on December 31, 2015. — Matt Pelikan

By the time Thanksgiving rolls around, pickings are getting pretty slim for a Vineyard insect enthusiast. On cool days, finding any insects at all can be a challenge. And even on warm days, you’ll find just a handful of species, as opposed to the scores that can readily be observed at the height of summer.

One of the most reliably detectable species in late autumn is the red-legged grasshopper, Melanoplus femurrubrum. If you know where to look, this species can be found well into December, long after all our other grasshoppers are done for the year. In seasons when we avoid sustained cold, red-legged grasshoppers even linger into the new year.

I don’t know if the persistence of this species into early winter actually reflects exceptional hardiness. Red-legged grasshopper is a very common insect, probably our most abundant grasshopper, and so what looks like resistance to cold may simply be the result of statistics: There are so many of this species to start with that at least a few are likely to hang on to exceptionally late dates.

Moreover, red-legged grasshoppers flourish later in the season than do most of their relatives. Freshly hatched nymphs of this species don’t seem to appear until late June or early July, when many other grasshoppers have reached full maturity. And I generally don’t see adult red-legged grasshoppers until late August or early September, when some grasshopper species are already done for the year. This schedule may make survival into winter more likely.

Still, this species appears to be a genuinely tough one. A light frost seems to produce no serious decline in their numbers. It takes temperatures down into the low 20s to produce much mortality, and at least a few of the individuals in our yard typically survive nights when the thermometer on our porch dips into the upper teens (with ground-level temperatures probably falling even lower). It takes either sustained cold or a deeply cold night to finish the last ones off.

Large and healthy individuals presumably resist the cold best, and so it’s no surprise that most of the late-season individuals I find are females: In grasshoppers, females are almost invariably larger than males. And there may be an element of luck involved: The longest-lasting individuals may simply be ones that happen to seek shelter in a spot with a warm microclimate, or perhaps even in a place where decaying plant material is producing a little heat.

In any event, it doesn’t take much to rouse whatever members of this species are still alive in December. I can find them in temperatures just a bit above freezing, if the sun is out, and the last survivors have a knack for finding spots where a house foundation or the corner of a fence collects the sun’s heat. As they age, the last holdouts grow darker in color and become less active. One day, the few that I find will be too moribund to fly; a few days later, I may find a single one too tired for more than a weak hop; and a few days after that, I don’t find any at all.

That’s a far cry from the status of this species in September, at the peak of its season. Red-legged grasshoppers occupy every dry, grassy habitat on the Island, and they may exist at remarkable densities. In some hay fields, I find a half-dozen or more per square yard, and every step I take through the grass produces a spray of panicked grasshoppers arching out in every direction.

This abundance surely translates into considerable ecological impact. I don’t know what they eat — presumably grasses, given their very clear habitat preference –— but the feeding of so many good-size insects surely translates into a significant negative impact on their favorite food plants. And their abundance makes red-legged grasshoppers a popular prey item among predators. Spider webs often snare them in mid-leap, and predatory insects like praying mantises and assassin bugs often eat this species, probably more from chance than from any real preference.

The species name is a bit odd because “femurrubrum” means “red femur,” referring to the upper segment or “thigh” of an insect leg. But it’s actually the tibia –— the next section down, analogous to our shin, that is red in this species! Anyway, this trait is almost useless for identification; many related grasshoppers also have red tibias, often of a much more intense shade of red.

Red-legged grasshoppers vary from brown to green in basic color; their undersides are almost invariably yellow, but the best field mark may simply be abundance: If you encounter huge numbers of similar grasshoppers in a field, chances are you’re looking at Melanoplus femurrubrum.

While my annual vigil for the final femurrubrum may seem melancholy, I have no concerns. Eggs for next year’s generation have been laid in the ground, and will hatch by the thousands next June. Eating, growing, and mating will occupy them for the next few months, until short days and cooling weather once more whittle a vast population down to the few final holdouts.