February 21, 2005
During the month of December of last year, few monarch butterfly adults, generally a female here and there laying eggs, no males I could sight, and virtually no surviving larva were observed, but beginning the first week of January, I began discovering surviving larva and as the month progressed, the number increased dramatically. At one point I had located over 100 larva at various stages of development on scarlet milkweed, A. curassavica. The temperatures were cool, generally between the high sixties, a few days of low seventies, and night time lows in the high thirties or low forties. We did not suffer a freeze or frost here though other inland areas of this part of Florida did.
The larva I brought in to raise with the exception of a handful have produced healthy butterflies. Some adults are a bit undersized, but most are full sized, and the number of pupa that were defective has been small, less than a dozen overall. The pupa are taking about 18 days to develop at current temperature ranges, about twice as long as in the warm months of summer.
Today, I finally did observe a male flying here, the first of the year which is most unusual. I do expect the number of adults in the air to begin increasing now, however. There have been several females visiting and laying eggs, but it seems, as far as larva, there is a gap, fewer being found, probably due to the current eggs belonging to another generation from the earlier butterflies. I have noticed increased wasp activity. They may be having some influence on survival. I'll know more when a week or two passes, and if the eggs hatch, the larva reach observable size.
As far as other butterflies, notably orange barred giant sulphurs have been around laying eggs on the cassia, I have brought larva in and raised several, and fritillaries on the passion vines. The fritillary larva are orange and have a white lateral stripe along the body. I suspect these are varigated fritillary larva as opossed to gulf fritillary larva which are solid orange.
Dr. Chip Taylor of the University of Kansas posted this interesting study concerning monarchs and temperature. This helps explain, to some degree, the problems associated with monarch butterlfly mortality in the summers here, a situation I call "The Florida Malady." For more info on this from my point of view, read the previous years postings. Its a little technical, but worth a read.
For a more complete explanation, see
DZmin (52.7) and DZmax (91.4) are temperatures at which monarchs will not grow. These are not lethal temperatures unless the insects ONLY experience temperatures below or above these limits for prolonged periods. My suggestion is that you use the formula and determine how it works with real data. If you dig deeper into the url, you will find examples in the appendices of how we applied degree days to max- min temperature data for KS and MN.
The basic formula is:
DD = (Tmax + Tmin) ÷ 2 - DZmin
if for a typical summer day Tmax = 88 and Tmin = 60, the equation is
DD = (88 + 60) ÷ 2 - 52.7 or DD = 74 - 52.7 = 21.3
that is, 21.3 degree days
On the other hand, if Tmax = 95 (greater than DZmax) and Tmin = 50 (less than DZmin) by substituting the DZ values for the for the temperature values, the equation becomes
DD = (91.4 + 52.7) ÷ 2 - 52.7 or DD = 72.05 - 52.7 = 19.3
that is, 19.3 degree days
My numbers for Florida in my location are narrower. At 54 degrees, monarch larva cease feeding, so the low end is a no brainer. However, my observations indicate the benchmark high here to be in the lower eighties. This is all relative to the species of milkweed, tropical in nature, A. curassavica.
April 10, 2005
For the past three weeks, I have once again been finding a number of surviving fifth instar wild monarch larva on the milkweed. I found only two today, and could not see any others, the milkweed being relatively depleted by foraging, but three adult females were present laying eggs. There are also several adult males on the wing here now.
I have been bringing the larva inside to raise to completion as I locate them. However, as the temperatures here are now closing in on daytime highs in the lower eighties, and the fact I also managed to swipe some milkweed sap into my eyes last week and had a nasty adverse reaction, I am expecting trouble. Obviously, the milkweed plant's chemistry has changed (I do wish I had a better scientific instrument to pick up this change other than my eyes. Through the winter, the plants are not nearly as toxic and I can handle them with little or no problem.) and that, along with the increasing temperatures, indicates the expectation of the onset of the "Florida malady," and sure enough, I am seeing an increase in mortality in the pupa. As usual, this is gradual with a handful of pupating larva a couple of weeks ago failing and over ninety-five percent healthy, to, at this observation, approxiamtely twenty per cent of the pupa now are showing signs of problems with also now some larva failing. I also received an email from south Florida from an individual now experiencing mortality in her pupa.
June 28, 2005
The monarch larva, although since my last post has been up and down insofar as survival percentages, have continued to decline. There are always some that make it, but fewer and fewer as the season, summer, that is, progresses. The last wild survivor was only a short while ago however. The butterfly, a male, I found as a fifth instar larva and brought inside for protection. Adults are flying every day, but I find no larva now.
The other butterflies are in full flight. I have seen giant swallowtails, palamedes swallowtails, polydamas swallowtails, giant sulphurs, eastern black swallowtails, white peacocks, southern whites (on the wane, their host plants are disappearing), and a number of other butterflies I have yet to identify.
December 2, 2005
On Thanksgiving Day, I found the first fifth instar monarch caterpillar surviving in the wild since my last post. Since, I located six more which should pupate today or tomorrow. The first one pupated on 11/25, but has yet to emerge. Notably, the larva are all being found on young, first year milkweed plants now only reaching about eight inches tall. The eggs these larva have come from were laid most likely in early November, possibly from fall migrants passing through. The mature, older plants, have had no larva on them, but that may soon change. A wasp nest I have been monitoring located under a leaf of a firebush plant just off the back porch is now abandoned and I believe the wasps have begun their winter dormancy. The weather has turned cooler, highs in the seventies and lows in the sixties or high fifties.
Adult monarchs are flying in fair numbers. I count six or so easily, but most are males, not many females. Females are around, but I've only spotted one or two lately laying eggs in the morning. They do not appear to reside long, just stop by and move on. The males, on the other hand, have set up resident territories and are dogfighting constantly.
We will post further observations as warranted.
St. Petersburg, FL
Thanks for visiting.
Dale & Peggy McClung