Signs of Spring 3: The Evolution of Butterflies and Moths

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(Thanks to Rob Bridges who passed along a newspaper article about these very interesting moth and butterfly fossils.)

Mourning cloak. Photo by D.G.E.Robertson, Wikimedia Commons

Butterflies and moths are collectively called the “lepidoptera” (“the scaly wings”), and they are very important signs of many of our seasons. In the early spring, mourning cloak butterflies emerge from their tree bark, hibernation crevices on those first, almost warm, sunny days of early March and flutter about sometimes over the still standing snow cover looking for potential mates. Then, in the late summer and early fall, monarchs migrate across our area (sadly, only in a hint of their formerly massive numbers). We see them first as they fly though on their ways to the northern edges of their summer breeding regions, and then again, later in the season, as their offspring fly back south toward their overwintering forests in the mountains of Mexico.

In between these spectacular seasonal bookends there is a glorious diversity of swallowtails, fritillaries, commas, sulfurs, skippers, sphinxes, lunas, and cecropias. Worldwide there are 160,000 species of moths (12,00 in North America) and 17,500 species of butterflies (760 in North America). Websites devoted to Pennsylvania moths and butterflies, though, usually only describe the 140 or so most common (or most abundant) species.  There is much more to these beautiful insects, though, than meets the untrained eye!

The life cycle of a lepidopteran is familiar to almost everyone: the early life stages (the larvae) are soft-bodied caterpillars that voraciously feed on plant leaves or other cellulose sources. The later life stages (the adults) are the actual winged moth or butterfly. These adults use their coiled, tubular mouthparts (called “proboscises”) to feed on fluids especially the sucrose-rich nectars generated by flowering plants. Each flower makes a very small amount of nectar, so butterflies and moths have to visit many flowers in order to get enough to eat.  As they make their trips from flower to flower they inadvertently pick up and transport pollen (a protein encased package of flower sperm) from one flower to another and, thus, fertilize the ova in each visited flower.

Hummingbird moth feeding. Photo by T.Hisgatt, Wikimedia Commons

Many elaborate flower anatomies are matched by lepidopteran proboscis structures, and it has been widely assumed that the present day anatomy of lepidopteran mouthparts is the consequence of their direct coevolution with flowering plants. The first flowers show up in the fossil record about 130 million years ago (MA). There are some controversial “flower fossils” dated to 162 MA, so a conservative date of origin of flowering plants is somewhere around 150 MA. Most previous studies suggest that moths evolved around 130 MA and butterflies significantly later (around 56 MA), so these time frames fit well into the plant/lepidopteran coevolutionary model.

Recent findings, though, challenge this very clear and very logical evolutionary explanation!

Fossils of moths and butterflies are not very abundant. Possibly this is because these insects are not common in habitats (like ponds and lakes) in which fossils most easily form, or possibly it is because their delicate bodies are not readily conserved in fossilized forms. One aspect of the lepidoptera, though, that is tough and resistant and readily fossilized are their wing scales, and this is what a team of German and American scientists found in some sedimentary rock cores from northern Germany that they were examining for fossilized plant pollen.

SEM of butterfly wing scale (x1000). Photo by SecretDisc, Wikimedia Commons

A diverse array of lepidopteran wing scales (suggesting a variety of species) were found in rock cores that date back to 200 MA! This is at least 50 million years before the evolution of flowers! So, the compelling question is, what were these ancient, fluid feeding moths living on if there were no flowers? (the research team’s findings are published in the January 10, 2018 issue of Science Advances).

Observation of present day moths and butterflies suggest some possible food sources for these “pre-flower” moths. Tree saps, for example,  are a potentially sugar-rich food stuff that is utilized by both butterflies and moths as a supplemental food in their nectar-dominated diets. Coniferous trees originated some 300 MA and were the dominant land plant of the Mesozoic Era. Breaks in the bark encasements of these conifers could have provided the first lepidopteran species with a sufficiently rich and reliable food supply to sustain them and could also have favored the evolution of tubular proboscises in these early moths. These tubular mouthparts, then, represent a pre-adaptation for subsequent use 50 million years later when flowers and their nectar food supplies came into being. Possibly, the mouthparts of the lepidopterans stimulated the anatomical evolution of flowers rather than vice-versa! The evolution of flowers, though, stimulated extensive speciation in moths and eventually led to the evolution of butterflies.

Comma butterfly. S. KIng, National Park Service

We will see the first mourning cloaks very soon. Then, on some sunny mid-March day, we will see the bright orange, comma butterfly (Polygonia spp.). The comma, like the mourning cloak, can overwinter as an adult and can thus take advantage of warm spring afternoons to feed on early nectars and get an early start on their spring reproduction. Often in late March we also see the tiny (1 inch across) spring azures. These stunningly beautiful butterflies have neon blue dorsal wing surfaces that seem to glow as they fly about. When they land, though, and close their wings, the blue color (and to all appearances, the butterfly itself!) disappears as the pale white under-wing coloration blends in to the surrounding browns and grays of the early spring vegetation. The spring azure overwinters as a chrysalis and finishes its metamorphosis into an adult even while snow still covers the ground.

The number and diversity of butterflies and moths will rise exponentially when we get into April and May. They are organisms that have been around 200 million years, and they still fill their ecosystems with grace and style!





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One Response to Signs of Spring 3: The Evolution of Butterflies and Moths

  1. Paul Hess says:

    Really nice summary of the lepids, Bill. Somehow I missed that paper in Science Advances, which I usually read.

    Incidentally, Dave Brooke and I saw a Chipping Sparrow on Tuesday at the Harrison Hills Environmental Learning Center feeders — two weeks before my usual first-of-year date in northeastern Allegheny County.

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