Bug o’the Week – Northern Metalmark Butterfly

Hi, BugFans,

Back in 2010, the BugLady wrote about the Swamp Metalmark, a lovely little butterfly that is fading from the Wisconsin scene and from other parts of its range in the Midwest (https://uwm.edu/field-station/swamp-metalmark/).  When she was in southern Ohio in June, she photographed a Northern Metalmark (Calephelis borealis).  Full disclosure: Northern Metalmarks are not found here; they occupy widely spaced pockets in a band from New Jersey/Connecticut on the east to southern Missouri/eastern Oklahoma on the west, but they don’t occur in Wisconsin.

northern metalmark

Metalmarks, family Riodinidae, are a mostly New World, mostly tropical bunch that includes about 1,100 species (20 north of the Rio Grande; some just barely).  They are smallish butterflies (Northern Metalmarks have a wingspan of about 1 ¼”) that typically perch with their wings spread wide, but that often fly into vegetation and perch, moth-like, on the undersides of leaves (makes them hard to census).  Females walk about on six legs, but males use only four – each of their front legs is greatly reduced and modified into a spine.  Males scan the airways for females from a perch, rather than on the wing.

Like many other metalmark species, Northern Metalmarks are subtly beautiful, with patterns of silver/metal/rust on dark wings.  They look very similar to Swamp Metalmarks, but habitat requirements separate them in areas where their ranges overlap.  Some species in the Southwest and the tropics are unapologetically spectacular https://bugguide.net/node/view/159108/bgimagehttps://bugguide.net/node/view/866024/bgimage, and https://bugguide.net/node/view/1024178/bgpage).  The tips of a NM male’s forewings are more rounded than are those of the female, and the undersides of his wings look pretty different than the upper sides https://bugguide.net/node/view/551483/bgimage.

swamp metalmark

Like the Swamp Metalmark (also pictured here), the Northern Metalmark has some very particular habitat needs, and like the Swamp Metalmark, this and other factors have put it on the threatened/endangered list in states where it occurs.  Another habitat specialist, the Lange’s Metalmark, is also endangered, (for an unusually-flowery-for-a-government-account of its revival efforts, see https://www.fws.gov/fieldnotes/regmap.cfm?arskey=36198.

NMs like open/dappled stream edges and meadows near woodlands with shale, limestone or serpentine rock barrens or outcroppings close by.  These are very sedentary butterflies, so the caterpillar food plants (two species of ragwort and one of fleabane) and adult nectaring plants must grow in close proximity.

Females place eggs, on at a time, on the underside of a host leaf, and the caterpillars, half-grown by the advent of cold weather, overwinter under the basal leaves of the host plant or burrow into the duff/soil, to emerge and continue their development in spring (for a picture of the caterpillar, scroll from page 74 to page 75 https://books.google.com/books?id=OWdD2bHSE-8C&pg=PA74&lpg=PA74&dq=northern+metalmark+caterpillar&source=bl&ots=Vd73rgy_-i&sig=mcQs6njQ7J7JAbn64Y6ik97tcCQ&hl=en&sa=X&ved=2ahUKEwj-rK3C79TfAhUm8YMKHXTDDCAQ6AEwDHoECAEQAQ#v=onepage&q=northern%20metalmark%20caterpillar&f=false).  Caterpillars form a chrysalis in spring, attached by a silk “button” to the underside of a host plant’s leaf.

Their historical range is believed to have been much larger.  Multiple factors have led to their decline, and it’s mostly a familiar chorus.

  • Habitat destruction or fragmentation due to development (although powerline rights-of-way can create favorable habitat), and successional changes that shade out the host plants.
  • Burning, mowing, or other management practices during the butterfly’s short reproductive season.
  • Pesticides, including Btk, a strain of bacteria that is deployed as a “nonchemical alternative” for killing gypsy moths and some other agricultural pests but that is lethal to an assortment of other moths and to some butterfly caterpillars (the BugLady is not a fan of collateral damage).
  • Invasives like barberry, autumn olive, and exotic grasses that shade out or crowd out the host plants.
  • Lifestyle – there are some endangered animals whose biology and lifestyle simply makes their whole existence seem improbable (think Giant Pandas, whose solitary females are fertile for only two or three days, once a year).  NMs (and SMs) need a particular geography seeded with a very limited selection of food plants, and they exist in small, isolated groups, often of fewer than a dozen individuals (a great formula for reduced fitness due to genetic in-breeding).  They fly low, and only for short distances, so if something does happen to their home place, they are unlikely/unable to move to another favorable spot.
  • And then there’s Butterfly vs Economy.  Where do the requirements of rare species (the canaries in our mineshafts) register on our civic scales?  Do/should the needs of a Northern Metalmark equal/surpass those of an individual or a community?  Is there a middle ground?  What is the applicable ethic, anyway?  The BugLady is recalling how, after the Dead Sea Scrolls were found, linguists were excited about how their understandings of some words were shifting, based on usage in those very old texts.  One case in point was the sentence “Increase, multiply, fill the earth and have dominion over it,” in which the verb that had always been translated “have dominion over” now seemed to be closer to “have stewardship over.

Legislating an environmental conscience results in resistance and resentment.  Can we educate for one.  At the very least we should remember, as Aldo Leopold noted, that “To keep every cog and wheel is the firstprecaution of intelligent tinkering.”  See “The Case of the Disappearing Butterfly” at https://www.nytimes.com/2008/08/10/nyregion/nyregionspecial2/10preservect.html.


[Editorial Aside: The BugLady gets solicitations all the time with pictures of the charismatic megafauna – gorillas, elephants, cheetahs, grizzlies, polar bears – and, yes, pandas.  Frankly, those animals seem almost fantastical to her – seeing them in the wild is not a part of her experience bank and is unlikely ever to be.  The groups for whom they are the poster children would have more success with her if they pictured the small, the winged, the six-legged, and the local.  There are four species of Federally Endangered birds in Wisconsin, three mammals, a reptile, five mussels (decidedly uncharismatic, those mussels), and four insect species.  The State Endangered and Threatened lists include five mammals, seven reptiles, 24 birds, 19 mussels, and 23 insects (https://dnr.wi.gov/files/PDF/pubs/er/ER001.pdf).  They need a bake sale, too.]

Apparently, the BugLady is starting out the New Year a little cranky.

Kate Redmond, The BugLady

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