A Five-Year Perspective on Our Extraordinary Season

A swarthy skipper, photo’d by Will Kerling at Lizard Tail Swamp Preserve, on May 23, still another new record early date for our five years of logging.

With the recent additions of swarthy skipper and cloudless sulphur we reached 63 species for the year the other day and so have now recorded approximately two-thirds of all species that we are likely to see this year. I thought it would be a good time for a look-back at the year so far, especially the pattern of early emergences we have witnessed.

How many species emerged early? Which species have been farthest ahead of their previous patterns? And how early have the emergences of all species been “on average”?

Click on the link below for a quick spreadsheet overview of the FOY (= first of year) dates for all 104 species we have recorded in our five years of logging, 2008-2012. Green = earliest date we have recorded in those years; yellow = second-earliest; and blue = latest FOY of the five years.

Charting Five Years of FOYs, 2008-2012

If you ignore all the green in the 2012 column for a moment, you will see that each of the previous years gave us a mix of early, late, and in-between emergers. In 2008, for example, three of the pierids (clouded, orange, and cloudless) emerged early, but two others (cabbage white and falcate orange-tip) emerged relatively late, as did several lycaenids, including brown elfin, Henry’s elfin, and holly azure. The majority of species, as majorities generally do, appeared on dates we might think of as average. Last year, 2011, several lycaenids were early (Henry’s elfin, gray hairstreak, red-banded hairstreak, and others) while some in that same group (juniper, white-m, and summer azure) flew for the first time later than in other years. Again, most species appeared on what seem average FOY dates.

Of course, that’s the typical sequence experienced butterflyers have come to expect most years: some species fly ahead of their expected flight times, others first appear behind their usual schedule, and the rest give us FOY dates between the extremes.

Not this year, though.

The green in the left-hand column tells the story. Of the 63 species so far recorded in southern NJ in 2012, 50(!) emerged earlier than we saw them in any of the previous four years.

Furthermore, 8 of the remaining 15 species are in yellow, as they emerged on the second-earliest date for 2008-12.

That leaves only 5 of 63 species that seem to qualify as “average emergers”: clouded sulphur (April 7), question mark (Feb 22), painted lady (April 17), and the two cloudywings — southern (May 11) and northern (May 12). The last species is the only one of the group earning blue as a late emerger, but that seems simply a result of the tight schedule that species apparently follows (early FOY date = May 5; late FOY = May 11) and our small sample size.

In truth: not a single one of the 63 butterfly species recorded so far in southern NJ has emerged on a date we can call genuinely late.

Hayhurst scallopwings photo’d by Dave Amadio is his garden on May 26. The FOY for the species came on May 14, tying our previous record early date.

To sum up, then: the vast majority of butterflies (50/63 = 79+%) have flown on a date earlier than any other we have recorded in our five years; most of the rest have also emerged early (on the second earliest date of our five years of data), and that makes our total of early flyers 58 of 63 species, 92+% of all that we have seen so far.

That seems a record that will be hard to match in future years…. unless global climate change is coming at us even faster and stronger than most scientists predict.

Ok, which species deserves the award for emerging farthest ahead of schedule?

A pure day-by-day count would seem to make the American snout of Feb 1 (earliest previous date = 5/2/10) the winner, with a close second place going to the common buckeye of Jan 29 (earliest previous record = 4/11/11).

However, both those species overwintered as adults (apparently), so we may want to give the award of “farthest ahead of schedule” to the sachem. This is a true “emerger” — eclosing from its chrysalis and flying for the first time in spring (or at least so we think?). Will Kerling found and photo’d a sachem on March 27, nearly six weeks earlier than the previous earliest FOY (5/2/10). Furthermore, he and other observers had eighteen subsequent observations of sachems at various spots, totaling 96 individuals, all before we reached May 2, that earliest previous FOY!

This is still another example that sachem is a species on the rise in southern NJ — emerging earlier, increasing in numbers, flying ever longer into the fall (up to Dec 4 in 2011). Something is happening with that little, nondescript butterfly. Does anyone have an explanation?

I realize I have been carrying on too long here and few readers will reach this point in this post. And that’s good. Because at this point I have to confess that finding how far ahead our butterflies have been “on average” involves math that is beyond my 6th grade abilities. For an accurate calculation, we would first have to determine the average emergence date for the previous four years, then count the days from that date to the date of emergence this year for each species, and finally average those differences for all 63 species. (If there’s a simpler or better way to do it, please let me know.)

As long as everyone promises to keep it a secret from my high school math teachers (whichever among those noble, patient folks are still walking this Earth), I am going to rely on the eyeball method. It looks to me that the average time-ahead seems to be one or two weeks or perhaps ten to fifteen days. Some species (the three species above, for example) were far ahead of that, and others are ahead less (or not all for the five “average emergers”). If anyone would be willing to do a more careful analysis, please add a comment below or send me an email. I will happily update this post and give you full credit. In the meantime, however, let’s call the average one to two weeks ahead of schedule, very approximately.

Ok, one last point and then I’ll end this:

“Observer bias” contributes as a factor in FOY data, it should be noted. We have more observers out in the field each year and the excitement of the early emergences this year seemed to push more of us out into the field, where we probably stayed a little longer and looked a little harder than in past years. The more of us out looking, the more we find, so our group as a whole will inevitably discover new early records. But that factor can’t explain this year’s startling pattern. The explosion of early emergers this year is significant and unlikely to be repeated soon. The warm winter and other factors have given South Jersey butterflyers an extraordinary spring that we will remember for a long time.

Keep exploring, everyone!


Question mark caterpillar photo’d by Cynthia Allen in her garden on May 22. The first brood of question mark was one of only five species not to appear earlier than its usual schedule.

Holly azure ovipositing on inkberry holly on May 21 on a Stockton College path. The next question: how late will our early flyers continue this year? What will our late date pattern look like?

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