This is part of the 2020 Digital Seaside Center. For more Digital Seaside Center content, click here.

Hello all! Welcome back to local wildlife weekly.

With summer winding down, many animals are on the move. The days are getting shorter, asters are beginning to bloom, and the bink-bink of migrating bobolinks floats down from overhead. To quote a notable house, “winter is coming.”

Don’t worry; we still have a ways to go. Personally, I find the breezy days of a waning summer some of our most idyllic. The slide from August to September is lazy and marked by clear blue skies, bright and spangled with insects. Perhaps you’ve noticed this abundance. Dragonflies cruise overhead, pollinators are busy in the weeds, and a myriad of butterflies– including the iconic monarch– are moving through on colorful wings. People often associate migration with birds alone and, while birds are certainly the champions of such journeys, we shouldn’t let them hog the spotlight– certain insects give birds a run for their money.

Insect migration can take many forms, but butterflies have perhaps the most “bird-like” migrations. They flutter with the wind, chasing seasons, and their movement is steadfast and spirited. It always seems that they know where to go. Many people think of butterfly wings as delicate, finely scaled, and they are– susceptible to damage from even the slightest touch. In light of this their migrations become the stuff of miracle: fragility melts to effortless strength and carries them hundreds of miles from home. In the journey of the butterfly I sense the same defiant vulnerability that carries small shorebirds over the sea, yet the butterfly– significantly more alien– never seems frightened or even aware. What to make of this? Lately I’ve been sitting in local gardens and watching butterflies go about; they are endlessly fascinating and I’ve been determined to profile one here. Choosing just one subject, however, has proven difficult.

This week, I was reminded of the perfect candidate. The common buckeye is a distinctive migratory species that, while unusual most of the year, becomes hyper-abundant along the shores of the Sound in late summer. It combines all the perfect ingredients: seasonal specialization, migratory behavior, intricate patterning… bingo! Given that you might now be seeing these butterflies each time you step outside, there’s no time to waste– let’s dive in.

Introducing: The Common Buckeye

A bright common buckeye at Sandy Point in West Haven, CT. Photo by Brendan Murtha.

The common buckeye, Junonia coenia, is what we call a “brush-footed butterfly” (family Nymphalidae). This large and variable group is named for the structure of their front-two legs, with are stunted and hairy. In the field these legs are often not visible, and so the butterflies appear to be perching on four legs alone. Don’t let this fool you, however– all insects have 6 legs, however modified some of those may be.

Brush-footed butterflies include many of our most recognizable species, including monarchs, fritillaries, admirals and the like. They are generally mid-sized butterflies and can be quite brightly colored, their flashiness contested only by certain local swallowtails (family Papilionidae). While buckeyes are mostly a dingy brown, the outer-reaches of their wings are patterned by a remarkable collage of bands and eye-spots. This gives them a distinct “calico” color-scheme largely unique in our area. While certain groups of butterfly can be an ID headache (I’m looking at you, skippers), brush-foots are generally not. Two other species of buckeye (genus Junonia) do live in the US, but these are highly localized in south Florida (mangrove buckeye) and the southwest (tropical buckeye): over most of the US, common buckeye is the default. This is pretty standard for North American butterflies: more so than many other groups, diversity is highly disproportionate between local strongholds and the rest of the country. Almost half of the 700 butterfly species found in North America fly in three south Texas counties alone, with south Florida and the desert southwest acting as similar sanctuaries. We have only ~100 species of butterfly in Connecticut, and many of these are widespread over large swaths of the country.

The common buckeye is one such species, but around here it’s only common during a narrow window in late summer. A migratory species, buckeyes overwinter as adults and can’t seem to weather the season further north than the Carolinas. Although some in the South stay on the wing year-round, others move north during the summer to populate weedy fields and gardens as far north as the border. The bulk of the population doesn’t make it past southern New England– as you head north buckeye abundance drops off fast– but those that do then turn south again in late summer/early fall, passing through our area as active passage migrants. The first buckeyes to arrive in our area during the summer often lay eggs and, by late August, the spike in numbers is a combination of “resident” adults, newly-hatched adults, and migrants from further north. During September all three demographic groups will head south for the winter, but the show is fun while it lasts.

One of the most fascinating aspects of butterflies’ natural history is their life-cycle, and the miraculous metamorphosis from caterpillar to winged adult. Despite this transformations’ long-standing hold over our collective imagination, relatively little is known about its mechanisms. When a caterpillar pupates in a chrysalis its soft body literally dissolves into a goo; the cells then re-arrange themselves to assemble the winged, adult body. What is truly remarkable here is that, within this goo, the individuality of the caterpillar/butterfly is conserved: scientists have shown that primitive memories transfer from the caterpillar’s lived experience to the adult butterfly. While the body dissolves, the self remains: a point for cartesian dualism, no? Of course, what this really indicates is that the constituents of individuality are ultimately inseparable from the body; within the chrysalis’s soup all bodily materials are retained, swirling around together, and the construct of memory must then be as physical as the body itself– just one ingredient in the pot! I recently saw an image of a partially metamorphosed monarch, extracted from its chrysalis, and it’s like something from a nightmare: the familar adult body is beginning to take form, but is soft and green and lifeless– congealing, one might say, from a primordial ooze. To reference another HBO show, I couldn’t help but think of the Westworld androids– bodily frames dipped in a silica gel, to harden– and my mind wanders to these timeless questions of self-hood, what it means to be human, living, and unequivocally you. Perhaps this is why humans have long-looked to the butterfly, for we sense they may have an answer.

The common buckeye, like many other butterflies, has a caterpillar that is specialized to feed on distinct host-plants. While all butterflies have some host-plant specifications, some are less picky than others. Larval buckeyes prefer plantains (genus Plantago, quite diverse) but will also feed on snap-dragons (genus Antirrhinum), monkey flowers, and more. Contrast this to the closely related mangrove buckeye which, as its name suggests, is specialized to black mangrove— that is the only plant adults will lay eggs on, the only plant upon which caterpillars will feed. This specialization of course restricts the mangrove buckeye’s range, so no wonder it’s a south Florida specialty! The disproportionate distribution of butterfly diversity should be understood partially through the lens of host-plant specialization: areas harboring unique plant-life will host unique and specialized butterflies, while wide homogenized areas (such as the eastern US, which is relatively uniform) are also more uniform in their butterfly assemblages.

Why specialize? This is the million-dollar question, it seems, when trying to wrap your head around the drivers and shapers of biological diversity. It is also a question I’ve touched on in these posts before, including last weeks piece on the eastern cicada killer. For butterflies (and by extension, caterpillars) specialization is best understood through three lenses.

First, as you might expect, specialization mitigates competition between species: if each butterfly sticks to its own plant, there will be more food for everyone. Think of a simple “tragedy of the commons” scenario (the “tragedy” is often mis-cited, but here I find it permissible). In this sense, specialization is good for the plants: plants do not want to be eaten, after all, and a caterpillar free-for-all would be impossible to manage. This leads to lens number two: specialization is often a by-product of an evolutionary arms race. Caterpillars are eating-machines (that is, truly, their singular objective) and can do a serious number on plants. Plants have thus responded to this threat by producing a dazzling array of defensive compounds. Some compounds are toxic, others merely distasteful. Certain compounds are smelly and make the herbivore odorous, obvious to predators, who then take the herbivore off the plants’ hands. Either way, the effect is the same: specialized herbivores are often those that develop a tolerance, or even a taste, for a specific plant’s compounds. They then can feed on the plant while others can not. This is obviously beneficial to the herbivore, and somewhat beneficial to the plant (in that the pool of threats has diminished). However, this doesn’t mean the plant-and-herbivore have reached a neutral agreement: the plant aims for zero predation, and develops new compounds, incentivizing further specialization… you can see how the arms race continues.

The third lens was already hinted at, but involves predation. Caterpillars, fat and soft-bodied, are the ideal prey item for many animals— songbirds especially have an insatiable taste for them. While a caterpillar could invest resources into producing spines and toxins (and some do), that’s a hassle— better to funnel resources into growth and pupate as fast as possible. As a result camouflage is the preferred method by which caterpillars avoid predation and, by the nature of camouflage, it only really works against a set background. Caterpillars are not going to be hopping between diverse plants, risking their visibility: best to play it safe and develop a camouflage highly effective against the backdrop of a specialized host-plant.

These three lenses are not to be taken as exhaustive, and host-plant specialization is not something that falls into one category or the other— often its long, complex evolutionary history is influenced by many factors, constantly in dialogue with each other. Furthermore, host-plant specialization can exist both upstream and downstream of a species’ range: painting a holistic picture of an organism’s natural history is remarkably difficult.

In the case of the buckeye, for example, its range is not set solely by host-past availability (although it’s surely a factor). It’s important to note that adult butterflies do not show the specialization their larvae do: feeding-on-nectar, many butterflies are functional generalists and will wander far outside their breeding range, untethered from the requirements of youth. Buckeyes are highly responsive to temperature, and large northward movements have been shown to follow anomalous heat-waves. Unsurprisingly, recent years have seen larger-than-usual buckeye influxes, as temperatures warm, and we can expect the northern edge of their wintering range to creep northward as well. Who knows— at some point in the future buckeyes could be resident along the Sound! Under that kind of warming scenario, however, buckeyes won’t be the only species expanding or retracting their range— what our species assemblages will look like is quite hard to predict.

I hope you learned something here, and if you happen to see a buckeye fluttering around these next few weeks be sure to say hello! All the big questions aside, they are fantastically beautiful and worthy of our time. We are fortunate to see them, and even more fortunate to count the passage of seasons on their wings.

Til next time! Cheers!

- Brendan Murtha, 2020 Seaside Center Naturalist