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Butterfly Forecasts for Central Iowa  
  September 2021  
  least skipperWe have let another summer slip past us.  The State Fair is over, kids are in school, and already we can notice the days getting shorter.
One butterfly has its only flight in late August and early September--Leonard's skipper.  This is a rare prairie obligate that is found in only a few locations in eastern and western Iowa. 
When the season for butterflies winds down there can still be a lot of butterfly activity.  Roadside patches of goldenrod or New England aster can be covered with butterflies.  Butterfly gardens and alfalfa fields can have a sky full of butterflies.  Unfortunately, I don't think that will happen so much this year because some of the species that can be so numerous are absent or at least pretty rare this year.  Red admirals are normally flying around in high numbers at this time of year.  They can be found this year, but numbers seem to be down.  The same can be said of painted ladies and American ladies.  I have not seen a little yellow all year.  Dainty sulfurs can't be seen in the areas I usually see them.  Those species can be extremely common in September, but I don't expect it this year.
We do have very good populations of monarchs this year, however.  They should start their migration within a week or so, and it will last most of the month.  If you are lucky you might be able to find a cluster of monarchs all roosting together for the night.  I don't know of any particular strategy for locating the roosting trees, but if you find them they can be quite spectacular.
We should also continue to have good populations of cabbage whites, orange and clouded sulfurs, and eastern tailed-blues.
Silver-spotted skippers will visit thistle flowers, landing on the underside and probing the flower with their long proboscis.  Many of the grass skippers become quite common in September, including fiery skipper and Sachem, least skipper, Peck's skipper, tawny-edged skipper, and common checkered skipper.
eastern commaIf you are lucky enough to have an apple tree you might consider leaving any extra fallen apples on the ground.  Insects of all kinds are attracted to the rotting apples.  That may include social wasps of several species--while they can sting, they tend not to in this situation because they are not defending a nest.  Butterflies go for the apples as well, and can provide a pretty entertaining spectacle if you if you are so inclined.  Watch for eastern commas, question marks, viceroys, red-spotted purples, and red admirals on the rotting fruit.
Most of Iowa's hairstreaks have only one generation per year, but the gray hairstreak has at least three.  Gray hairstreaks can become almost common late in the year, and can be quite beautiful as well.
While browsing the iNaturalist sightings from August I noticed that there was a white m hairstreak seen near Saylorville.  This is a very rare butterfly (which can be mistaken for a gray hairstreak when seen from the side).  There were also some sightings of harvesters near Iowa City.
Enjoy the cooler weather and watch for butterflies while you can.  Soon the season will be over and it will seem like a long time before we will see the 2022 butterflies.
 
  grapeleaf skeletonizer  
  August 2021  
  giant swallowtailButterflies have three different survival strategies for making it through the harshness of Iowa's seasons.  A large group of them spend the winter here in one of their life stages.  A second group migrates.  Monarchs are the best known example, but others such as red admirals and painted ladies also migrate.  Individuals can be observed to travel in a particular direction during the migrations--flying north in the spring or early summer and south in late summer or fall.  A third group resides mainly in states to the south of us where they build up large populations that disperse widely so that numbers end up here.  This is different from migration because there does not seem to be a return flight.  So we have residents, migrators, and dispersers. 
 But butterflies don't always follow the rules, and we don't always have enough information to properly classify all of them.
Migrators can have huge population fluctuations from year to year.  Monarchs are present in pretty good numbers this year, but most of the other migrators are not doing so well.  Red admirals can be found, but in much lower numbers than normal.  Painted ladies and American ladies have been mostly gone.  Chris Edwards noted in his NABA counts that he had not seen common buckeyes (another of the migrators) this year.  I have not seen them noted on iNaturalist, nor were there any this year reported on Jim Durbin's Insects of Iowa website.  Little yellows may migrate but seem to be more of a disperser group (with no southward migration at the end of the season).  I have not seen one this year, or a record of one.  Overall, butterfly numbers this year are about normal, but with some species that are absent or have greatly reduced numbers.pearl crescents
Black, eastern tiger, and giant swallowtails will be present for the entire month in the central parts of the state.  Zebra swallowtails may occasionally stray into the area, but have resident colonies in the extreme southeastern and southwestern corners of the state and can usually be found there.
Cabbage whites, clouded sulfurs, and orange sulfurs should be present in large numbers.  Cloudless sulfurs are always thrilling to find, as they are considerably larger than the other yellow butterflies, although not nearly as common.
Summer azures and eastern tailed-blues will be the most common blue species.  Hairstreaks are mostly gone, with the exception of the gray hairstreak which will persist until the season is over.
Large fritillaries like the regal and great spangled typically have only generation per year, with a peak in early July.  You might see them for the next week or two, but they will be old and pretty much battered up.  Pearl crescents and silvery and gorgone checkerspots can become quite common over the next month or two.  Be sure also to keep an eye out for the American snout.  This butterfly can form huge population explosions in states to the south of us (especially Texas), but usually we only see a few in the late summer here.
Some skippers can become quite common in August.  Silver-spotted, common checkered, common sootywing, Peck's, and tawny-edged skippers are all resident skippers that have multiple generations in Iowa.  Fiery skipper and sachem do not over-winter in Iowa (most years), and disperse into the state late in the year. 
Already the days are getting shorter.  The butterfly season is still with us, but will be gone before we know it.  Get outside and enjoy it while you can.
 
  Grapeleaf skeletonizer  
  July 2021  
  Red-spotted purpleJuly is the peak month for butterfly diversity in Iowa.  Population sizes will increase over the summer, but the number of species you could possibly see is at its peak right now.  Of Iowa's butterfly species, more have a flight period that includes July than for any other month.
June started out pretty slow.  We have had extremely dry weather, drought in some areas, and that affects the butterflies.  Some of the normally very common species are less common than usual.  Red admirals and eastern tailed blues would normally be found in the typical backyard in high numbers.  They can still be seen, but their numbers are way down.  Other species can benefit from the conditions.  Hackberry emperors have had huge population explosions (called irruptions) in several of the wooded state parks.  I visited Waubonsie State Park in the south west corner of the state in mid June and saw hundreds of hackberry emperors scattered along the blacktop roads and in huge clusters on dry gravel access roads, all doing the typical mudding behaviors.
The tawny emperor is very similar to hackberry, using the same host plants and with similar habitats.  It is much less common than the hackberry in Iowa, but a similar population explosion of this species in Shimek State Forest was documented by Chris Edwards.
Mark Brown posted a photo of an aberrant pearl crescent to the Iowa Butterflies Facebook page.  It was a very unusual find, and good detective work on his part to understand what it was.  Aberrant butterflies can just be some unusual genetics as with the regal fritillary shown on this page.  Eastern tiger swallowtails have different morphs based on sex, and can sometimes have characteristics of different sexes on the same butterfly.  The red-spotted purple is considered a subspecies of a species that includes it and another butterfly called the white admiral.  Hybrids of the two subspecies can sometimes occur naturally.  Viceroys are in the same genus, and sometimes hybrids of red spotted purple x viceroy can occur.little yellow 
All of the swallowtail butterflies should be possible in July.  The big three in this area are giant, eastern tiger, and black swallowtails.  Zebra swallowtails are mostly restricted to extreme southeastern and extreme southwestern locations in Iowa but some individuals have been spotted in the middle of the state this year.
Orange and clouded sulfurs typically reach high numbers in July, and migrators like little yellow and cloudless sulfur can start to appear.
Look for some of the hairstreaks in savanna areas.  They can often be found on common or butterfly milkweed, or can be seen chasing each other around their host trees.  Banded, Edward's, and coral are common enough that they might be reliably located.  Hickory and striped hairstreaks are less likely in this area.  Juniper hairstreaks have a second generation that appears in July although it is probably most reliable in the loess hills area.
If you walk through a prairie area you will likely encounter common wood-nymphs, which fly up from the grasses then dive down into them.  Of course, check flowers and hilltops for regal fritillaries.  Great spangled fritillaries will be quite common and frequently encountered.  Red admiral, painted lady, and American lady populations have been down compared to normal years, but you will still find them.  Pearl crescents and silvery checkerspots can be quite common.  I have encountered a surprising number of gorgone checkerspots this year in areas where I did not expect to find them.  Monarch numbers are normal or better than normal this year.
Swamp milkweed will bloom later this month after most of the common milkweed is done.  Swamp milkweed is a spectacular pink color and is a great place to try your butterfly photography skills.  It mostly attracts only large butterflies and large wasps.
When we get thunderstorms in July we can get a lot of rain in a very short period of time.  It cools down during the rain, then when the sun comes out it gets hot again.  That is a great time to walk along gravel roads to watch for butterflies mudding.  That is also a great time to test your photography skills if you don't mind getting sand and mud on your knees and elbows.  Get out and enjoy it, and don't get run over by a car.
 
  Grapeleaf skeletonizer  
  June 2021  
  Joel Asaph Allen was a zoologist and ornithologist who was a curator of birds and mammals at the American Museum of Natural History.  In that capacity, he would often take field trips to such exotic locations as Brazil, Florida, and the great plains.  gray copperOn one of those trips, in June of 1869, he visited Denison and New Jefferson, Iowa.  In addition to collecting birds and mammals he collected some butterfly specimens which he gave to Samuel Hubbard Scudder, one of the leading entomologists at the time.  Mr. Scudder published a description of the species as Chrysophanus dione.   It turned out to be a new species, discovered in the young state of Iowa.
Gray coppers seem to like prairie or old field habitats.  If you see one there are likely to be a lot more around when you look for them.  They are very visible, being large for gossamer-winged butterflies.  In Iowa, they have one generation only and fly from mid June to mid July.
In Iowa, June is the start of the busiest time for butterflies.  Many of the species that have only one generation per year fly when the days are the longest.  Species that have more than one generation each season will start their second flight in June.  The numbers rapidly increase.  With the longer days, you will have many more opportunities to encounter butterflies as well.
The first generation of eastern tiger giant swallowtails will persist through June, with the second generation appearing in July.  Black swallowtails can have several generations with steadily increasing numbers throughout the summer.  These butterflies are large and have fairly long adult life spans.  If you have large showy flowers in your garden, you might see particular individual members of those species visiting the same flower at approximately the same time each day.  Red admiral behavior is also fun to follow--late in the day, near sunset time, individuals will bask on tree trunks or on the side of a house, or even on different structures in your yard.  They chase any other butterfly they see, regardless of the species, then often return to the same spot to bask again.  They might return to a particular prime location for several evenings in a row.American lady
Cabbage white, clouded sulfur, and orange sulfur all become very common in June, and can be seen almost anywhere.  You may see little yellow anywhere its host plant partridge pea is found.  Look for dainty sulfur in the sandy areas along the Des Moines River.  They seem to be associated with the
cockleburs that grow in those locations.
There are a number of hairstreaks and grass skippers that have only one generation per year and fly in June.  A surprisingly high percentage of them can be found by inspecting common milkweed flowers on a regular basis.  You might also check dogbane and other types of milkweeds.
Purple cone flowers are good as well.  The point is to watch them on a regular basis and look for the small, easily overlooked butterflies that you might not see otherwise.  Watch for banded and coral hairstreaks, Peck's, Delaware, tawny-edged, and crossline skippers.  You may see other species that are less common as well.
Most of the brushfoot butterflies can be seen in June.  Painted ladies and American ladies can be found almost anywhere.  Watch for question marks mudding along trails in wooded areas.  Northern pearly-eyes and little wood satyrs can also be found along woodland trails.  Red-spotted purples and viceroys can also be seen easily.
One of the spectacular butterflies that can be seen most of the summer is the great spangled fritillary.  It is quite large, and visits backyard flower gardens readily.  It seems to have just one generation per year, although there can be fresh individuals for most of the summer.
You should plan on making a trip to a prairie sometime in late June or early July to look for regal fritillaries.  There have been good numbers in recent years, but typically they are only found in good prairie habitat.  This is a spectacular, monarch-sized brown butterfly, and well worth the time and effort needed to see them.
Days are long in June and butterflying is good.  But the season passes by fast, and you can miss the show if you are not outside.  So get outside and watch for butterflies.
 
   
  May 2021  
  Eastern tailed-bluesApril has had weather which has been somewhat inconsistent for butterflies--cool windy days, mixed with the occasional warm day.  We have even had some snow and frost.  We have had some good butterfly days and some bad butterfly days.  May should have days that are consistently better for butterflies, and the populations should start to increase.
Redbuds grow naturally in the southern third of Iowa.  If you hit one of those places--Red Haw, Elk Rock, Cordova, or Waubonsie State Parks to name just a few, and you look closely at the redbud trees or along the walking paths near those trees you might see a very small butterfly that looks black--Henry's elfin.  It is more of a brown color than black when you get the light on them, but they look black initially. Their flight only lasts for a few weeks in late April or May.  If you get out during the first week of May you might find some, or you might just be too late.  Henry's elfin can be quite frustrating.  I spent many hours looking for them before I finally had a little bit of success.
Cabbage whites have been on the wing, as have clouded sulfurs.  I have only seen one eastern tailed-blue so far, but I expect them to be out in large numbers soon.
I noticed what I thought was an abnormal absence of red admirals when I started writing this forecast, so I asked the expert on the species, Royce Bitzer, what was going on.  If you remember, a small fraction of this species seems to over-winter in Iowa, but most migrate in from states to the south of us.  Royce pointed out that we had a pretty cool spring, the jet stream was far to the south of us, and we had not had winds from the south that were warm enough (above 60 degrees F) and which had a high enough humidity (dew points above 55 degrees F) to support the migration.  Normally we have those conditions by mid-April, and this year we did not get those conditions until April 26.  So the bottom line is, the red admiral migration came a little late this year.  I have noticed that we are now getting good numbers of red admiral sightings on the web sites that track those things.
The butterfly numbers in May can be low.  Multi-generational butterflies have peak populations when most of the adults are flying, and May happens to fall between the peaks for most species.  eastern tiger swallowtail
The swallowtail species should be out.  The big three for central Iowa are the black swallowtail, the eastern tiger swallowtail, and the giant swallowtail.  The black swallowtail can be found in open fields.  Watch for the other two on flowering trees.  Crab apples, lilacs, or fruit trees are always good places to look for them. 
If you happen to live in either southwestern Iowa or southeastern Iowa, zebra swallowtails can be found in Waubonsie State Park and is Shimek State Forest.
Look for American ladies and painted ladies this month.  I usually see American ladies a little bit earlier than I see painted ladies.
Meadow fritillaries have been photographed in Iowa by several people.  They can be common in certain habitats.
Skippers that show up in May include the silver-spotted skipper, Peck's skipper, hobomok skipper, and the common sooty wing. 
Dusky wing skippers that are flying include Horace's, Juneval's, and wild indigo.  There are a few others that are rarer than those three.  All are difficult to identify even with a good photograph.
The weather is turning nice, and it is time to get outside and replace that Covid-19 paleness with a good tan.  You won't be sorry that you did.

Harlan Ratcliff
 
  Grapeleaf skeletonizer  
  March and April 2021  
 
Mourning cloakButterfly season is upon us.  Hopefully it is coming up fast.  But it doesn't come in with a bang. The sky will not be filled with butterflies. Instead, the season comes in with two or three species sunning themselves high on a tree trunk, or sipping sap from cracks in the bark where tree limbs have broken, or from holes in the bark drilled by sapsuckers.
While the late summer days with lots of butterflies are great, so are the early spring days after a long winter when you see just one or two little bits of optimism flitting around.
Butterflies which spend the summer as adults are the first you will see.  Around here they are the mourning cloak, the eastern comma, and the gray comma.  Compton tortoiseshell and Milbert's tortoiseshell also overwinter as adults, but are extremely rare in central Iowa.  You might see them if you are in northeastern Iowa, however.
The other butterfly you might see very early on is the red admiral.  Red admirals migrate into Iowa from southern states, but it seems likely that the early ones are the result of individuals which spent the winter in the pupa stage rather than migrate in.
As we get into the (usually) warmer weather of April we will start seeing other butterflies that have recently emerged from their chrysalis rather than just those that spent the winter in the adult stage.  We will also see the other migratory Vanessa species, the painted and American ladies.  The early April species include the cabbage white and the black swallowtail. red admiral Olympia marble was formerly found in central Iowa in small numbers, but is probably not present now.  However, it is a very secretive species and could be here and not seen.  If present, it would fly in early to mid April into very early May.  Unfortunately, it is most likely gone. 
In mid to late April you may be able to find spring azure in some of the wooded areas.  Henry's elfin uses redbud as a caterpillar host plant, and is found about the time that small tree blooms.  Look for it in the wooded areas along the Des Moines River, anywhere south and east of the city of Des Moines, and where there are concentrations of redbud.  I have found them on the ground or in low vegetation along walking trails.
By late April a good assortment of butterflies should be flying, including the eastern tiger swallowtail, clouded sulfurs, eastern tailed blues, juniper hairstreaks (they are found in central Iowa but are pretty rare here), pearl crescents, and question marks.
I usually admonish people to get outside and away from their screens during butterfly season, but there are some pretty good resources that are worth checking out which can enhance the experience.  The first is the book The Butterflies of Iowa by Dennis Schlicht, John Downey, and Jeffery Nekola.  It was published in 2007, and your library may have a copy. Amazon does seem to have some used copies for sale.  This book gives a lot of information about Iowa's butterflies that is more specific than the general field guides give.
Jim Durbin's Insects of Iowa site gives information on recent records for Iowa's butterflies.  Royce Bitzer, Ph.D. has a website with lots of good information about the migration patterns of red admirals and the painted lady species.  The Wisconsin Butterflies site tracks Wisconsin butterflies, but has a useful "recent sightings" page that tells us that mourning cloaks have been seen in Wisconsin, with the first of the year seen on March 8th.  inaturalist seems to have some really good information about butterflies but also records of a whole host of other species.  There is also an Iowa Butterflies Facebook page.  e-butterfly,  Butterflies and Moths of North America (BAMNA) and BugGuide all give useful regional information.
Last year was difficult.  Many of the state parks had restrictions.  Let's hope this year is better.  Butterflying is an activity that can be enjoyed individually or in small groups, but maybe some of the more social events can happen this year as well.
So get your nose out of the internet and get outside and look for butterflies.
 
  Grapeleaf skeletonizer