Celastrina Azures in Manhattan: What Do We Know?

This lovely shot by @ansel_oommen depicts a Summer Azure (Celastrina neglecta) during July in Central Park, with a characteristically pale, whitish underside; small, fine dark markings; no strong marginal markings on the hindwing; and a white, unmarked fringe on the hindwing.

Introduction

Celastrina is a genus of small gossamer-winged butterflies (family Lycaenidae) with species distributed across North America, the Palearctic, and tropical Asia through Wallacea to New Guinea. In North America, Celastrina species are generally called azures.

Eastern North America holds quite a complex tapestry of similar-looking azure species. These species differ in timing of flights, number of broods, and host plant choices, and locality matters a lot -- what's true in one place may not be in another. Flight dates, number of broods, and host plant choice can all vary across a species’ range, and appearance can vary seasonally, all greatly complicating identification. This recent paper from @bryanpfeiffer summarizes several of the issues with this group: https://bryanpfeiffer.com/wp-content/uploads/2018/04/Getting-the-Blues-Celastrina-2Apr2018.pdf.

What About Manhattan?

Several Celastrina azure species fly within 50 miles of Central Park, but which azures occur specifically in Manhattan's urban parks and small islands? It currently appears that only the Summer Azure (Celastrina neglecta) occurs in New York County, flying from late May to mid-October. The species’ peak abundance appears to occur in June and July, and it appears to utilize a variety of host plants in Manhattan.

How do we arrive at this hypothesis?

First, here are the currently accepted species (following Pelham 2020 with iNaturalist’s common names) that occur in the tri-state area (NY-CT-NJ), arranged in rough order of flight times at our latitude and with a few notes relevant to our region:

  • Celastrina lucia (Lucia Azure). Flight: March-April, and possibly later. Broods: 1-2+. Range: High latitudes and elevations across North America, nearing southern limit of its range in the greater NYC area. Appearance: Often dark grayish below and heavily marked, but variable. Notes: Recently shown to have both spring and summer flights in southern Ontario: https://zookeys.pensoft.net/article/7882/.
  • Celastrina ladon (Spring Azure). Flight: March-April/early May. Broods: 1. Range: Widespread in eastern U.S. but range not fully understood. Appearance: Often lighter than C. lucia but with somewhat dark ventral hindwing margin. Crucially, males have a distinctive dorsal wing scale morphology visible under magnification. Notes: See notes on distribution, wing scales, and introgression with C. lucia and C. neglecta which can cause males of those two species to show the distinctive C. ladon male wing scale morphology here: https://www.researchgate.net/publication/331939185_New_thoughts_on_Celastrina_in_Florida)
  • Celastrina idella (Holly Azure). Flight: Spring. Notes: Occurs south of NYC, from central New Jersey along the Atlantic Coastal plain, utilizing native hollies as host plants. Described in 1999: https://leplog.files.wordpress.com/2011/03/pavulaan-wright-1999-taxonomic-rpt-on-c-idella3.pdf
  • Celastrina serotina (Cherry Gall Azure). Flight: May-June. Broods: 1. Range: Northeastern U.S. Appearance: Whitish below often with fairly bold dark markings and fairly white hindwing fringe. Notes: Uses mite galls on native Prunus cherry leaves as larval food (https://www.flickr.com/photos/mcrainey/4680056033/), but will use other host plants too (and C. lucia larva recently shown also to use cherry galls in paper linked above). Described in 2005: https://leplog.files.wordpress.com/2014/04/pavulaan-wright-2005-c-serotina.pdf.
  • Celastrina neglecta (Summer Azure). Flight: late May-October. Broods: Multiple. Range: Widespread east of the Great Plains. Appearance: Whitish underside with reduced markings and white hindwing fringe. Notes: Uses a variety of host plants and has multiple broods annually.
  • Celastrina neglectamajor (Appalachian Azure). Flight: Overlaps with C. neglecta. Broods: 1. Range: Appalachian Mountains and nearby areas where its host plant grows. Appearance: Very similar to C. neglecta. Notes: Only one host plant: Actaea racemosa (Black Cohosh).

When we examine iNaturalist reports for Celastrina azures in New York County, New York (and iNaturalist provides by far the most abundant publicly available data on this question), we see that there are currently zero Celastrina records in Manhattan in March or April. In fact, the first report across any year is not until May 23. This is particularly noteworthy because the City Nature Challenge in late April results in a large number of observations submitted to iNaturalist, relative to other months. As of March 2020, there are approximately 23,400 iNaturalist observations of all taxa in April (all years combined) vs. 14,500 in May and 12,700 in June. However, there are zero Celastrina observations in April, a handful in May, and nearly 30 in June. If azures were regularly flying by late April in Manhattan, it seems likely that someone would have reported one. After a sporadic showing in late May, azures peak in Manhattan in June and July and taper off through August, September, and into October, according to iNaturalist reports.

The absence of March, April, or early to mid-May azure reports argues strongly that neither C. lucia nor C. ladon have populations in Manhattan. Even if C. lucia has a second, summer-flying brood in our broader region, there is no evidence of a spring brood in Manhattan, so there would be no summer brood.

The late-May start date for our azure flight (and the visual appearance of those May individuals, with very light markings on their ventral hindwings) also seems likely to rule out C. serotina, though more careful observation might be worthwhile. Late May is when the first C. neglecta would be expected to emerge, and C. neglecta is known to have multiple broods through the summer, which tracks the distribution curve present in iNaturalist data so far.

What of C. neglectamajor? The Appalachian Azure is very similar to the Summer Azure, but it uses only one host plant: Actaea racemosa (Black Cohosh), at a specific stage of flower bud development. There are likely no wild stands of the plant in Manhattan, and though it is cultivated in Central Park and probably other parks, its presence there is strongly isolated from native stands, probably making a population of this specialist butterfly unlikely. (Note that Summer Azure will also use Black Cohosh as a host plant: https://groups.google.com/forum/#!searchin/nyleps/appalachian$20azure%7Csort:date/nyleps/oOFQyzKGDy4/nerW9rrEBQAJ)

It is not clear exactly why C. lucia, C. ladon, and C. serotina should not occur in Manhattan. Some of their host plants grow prolifically in our parks and between the cracks of civilization. Perhaps habitat fragmentation or urban pressures are too intense for them. Or perhaps we need to pay more attention.

Harry Pavulaan is one of the people who has contributed most to our understanding of azure ecology and taxonomy in the last 30 years (describing, with David Wright, both C. idella and C. serotina). So, I asked him this month what he knew about azure distribution in Manhattan. Citing New York City Butterfly Club data, he agreed that C. neglecta is likely our only azure.

Further Research: How You Can Help

Is this the last word on Celastrina in Manhattan? I hope not! If there's one thing we know about Celastrina azures, it's that they're full of secrets and surprises. They reward careful and patient observation.

Other azure species do occasionally turn up in NYC's outer boroughs. For example @cesarcastillo photographed this individual in mid-March in Alley Park, Queens, a couple of years ago: https://www.inaturalist.org/observations/15392436. A similar-looking individual was photographed at Wave Hill in The Bronx last week: https://www.inaturalist.org/observations/39879555. And @christophereliot photographed this very dark individual in Prospect Park, Brooklyn, on May 1 two years ago: https://www.inaturalist.org/observations/12006196.

Could there be other azures showing up around the edges of Manhattan, at Inwood Hill Park, or on Randalls or Governors islands? Maybe, and now is the time to start looking, as we officially mark the arrival of spring after a historically mild winter.

If you did find an early azure, and it were a male, high-magnification photographs of the upper wing surface showing the details of the scales would be extremely useful.

Connecting azures to host plants in Manhattan would be another useful line of exploration. Right now, iNaturalist has two records of female Summer Azures ovipositing on flower buds: this one from @kasimac (on Salvia) and this one from @filiperibeiro, apparently on some sort of shrubby Cornus -- can anyone ID that plant?

If you can catch azures ovipositing (or in their tiny, obscure larval form) and document the plant, that could be very interesting information. And as May and June unfold, keep an eye on cherry leaf galls and young Black Cohosh flower spikes if you want to be the first to document C. serotina or C. neglectamajor in Manhattan. Are they here and just overlooked? Or do they truly not occur in an area of such human density? Right now, all we know for sure is that they haven't been documented yet.

Two general reminders: Butterflies of Manhattan project is here: https://www.inaturalist.org/projects/butterflies-of-new-york-county-manhattan, and checklist-in-progress with monthly abundance graphs is here: https://docs.google.com/spreadsheets/d/1Y2mNKMNXqtk4Ms820YvKXaaTySSYoxtcGlq7znoCjtY/edit?usp=sharing.

Joyous Vernal Equinox, and thanks to Harry Pavulaan and all of you who contribute your observations and expertise. Be healthy and well.

Tagging some of you who contribute a lot of butterfly observations and/or IDs in New York as an FYI: @blkvulture @cathyweiner @craghorne @danielatha @greengenes @kdstutzman @kenchaya @klodonnell @maractwin @nlblock @nycbirder @nycnatureobserver @pawelp @sadawolk @spritelink @steven-cyclist @susanhewitt @wayne_fidler @zahnerphoto

Posted by djringer djringer, March 19, 2020 13:04

Comments

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Wow, this is a great write up! I think I'll show this post to my students as an example of how great the iNaturalist community is and what you can do with iNat besides just uploading observations. Assuming (hoping) that we are done with this pandemic by the September, we'll make sure to be on the look out for these at our annual BioBlitz.

Posted by klodonnell 5 months ago (Flag)
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Great stuff, @djringer!

Posted by nlblock 5 months ago (Flag)
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Great article. Not manhattan, but I also have this sighting from April of last year.. I'm no expert on Celastrina, but I hope the ID is correct.

https://www.inaturalist.org/observations/22491390

Posted by cesarcastillo 5 months ago (Flag)
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Interesting read.

Posted by pawelp 5 months ago (Flag)
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This is a really outstanding example of the potential value of iNaturalist. Thanks for the superb information and analysis.

Posted by kennkaufman 5 months ago (Flag)
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Great piece of information, @djringer.

Posted by miriamht 3 months ago (Flag)

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