'Tis the season for Black Swallowtail caterpillars

The rather unimpressive greenery around our mailbox is a confluent group of rue (Ruta graveolens).  Most homeowners opt for mailbox plantings that are a bit more colorful and showy.  We like the rue because this shrubby perennial tolerates poor soil in hot dry conditions (next to an asphalt road and concrete driveway) and because it is a primary food plant for the caterpillars of the Black Swallowtail (Papilio polyxenes).

Earlier in the season the plants are covered with tiny yellow blossoms...

... which, while unspectacular to the human eye, are complex clusters of five-petaled flowers that are very attractive to bees.  We seldom see Black Swallowtail butterflies on the rue (they tend to nectar on larger flowers elsewhere in the garden), but we know females have visited the rue and oviposited there because in September the caterpillars start appearing on the upper outer branches.

What we see are the late-stage instars, mature caterpillars that are starting to look for a place to form a chrysalis.  They seem to know that the greenery of the rue will die back in the winter, leaving only the woody central stems, and they need a secure place for the chrysalis if they are to live through a Wisconsin winter.

When we find the caterpillars, we bring them to our screen porch, which offers them protection from predatory wasps, ants, spiders, etc., and we give them some clippings of the rue for a final snack, and more importantly a variety of sticks they can use for pupation.  In the above photo the two caterpillars have chosen a stick from a birch tree, and the one on the right has already formed its "J", with a silk harness going from the stick around behind its "shoulders."

Several days later (the larger cat having moved on), the caterpillar is now fully pupated, attached at the bottom with some glued adhesive [higher on the stick is a remnant from a prior year's successful sequence], and supported by that amazing little silk sling.

We have eight of these now on the screen porch.  The terrarium will be placed where the chrysalises can be snowed on (I think they might need some moisture in the winter to avoid desiccation), and they will live through sub-zero temperatures, will freeze and thaw (perhaps several times), and in the spring...

... magic.

I've seen metamorphosis countless times, and it never fails to fascinate me.  And the beauty of these creatures up close in just incredible.  Here's a view of the underside of the wings -

And then follows the to-me-incredible event when a creature that in its entire previous life crawled around in a small plant, now lets go of a stick and "knows" how to fly.  And eyes that have never before focused more than millimeters away can now locate food and mates at dozens of meters.

You don't have to be a child to retain a sense of wonder with regard to the natural world.

Black Swallowtail (Papilio polyxenes) caterpillar. Updated with egg and first instar.

Remember the golden spherical Black Swallowtail egg I posted on the June 8 linkdump?  In due time it hatched and the little fellow has been happily munching away on some bronze fennel and Queen Anne's Lace.  He's living on our screen porch protected from parasitic wasps, so I should be able to document the full life cycle for the blog.

You can click to embiggify, but the image is not quite sharp because when I took this photo a couple days ago I used a long lens to isolate him against a blurred background, and thus didn't get quite enough depth of field to get all of his spectacular body features in focus.

And meanwhile -

-  I spotted another BST hovering over the rue we have planted by the mailbox.  She was oblivious to my approach, intent on ovipositing.  Frankly, if I had not seen her zoom in on this particular inflorescence of the rue, I would never have been able to spot the fiendishly-well-camouflaged greenish-yellow egg on the stamen of the greenish-yellow flowers.

Addendum:  On the sixth day after the above photo was taken, the egg now appears dark:

When I zoom in maximally, I believe I can see three black stripes inside the greyish-black egg, suggesting that it's about ready to hatch.

Update:  Just 3-4 hours after the photo above I looked again, and the first instar had emerged:

I'm always amazed how much bigger first instars look than the eggs they come out of; they must be tremendously compressed in there, or perhaps the new caterpillar is mostly air on the inside.

It probably ate the egg capsule for its first meal; I hope it will be satisfied with the stamen or pollen or a petal for the next day or two, because it's so small I'm reluctant to try to transfer it to a fresher rue blossom on a stem with leaves.  (The annonyingly inappropriate black filament is probably a cat hair; they like to explore the work table).

Black swallowtail (Papilio polyxenes) beginning metamorphosis

Here's some real hope and change.  Some of you will remember the Black Swallowtail egg that made its debut here on a June 8 linkdump.

What emerged from that egg was a caterpillar whose color pattern changed from an initial black-with-yellow-spots to show a green between the black as his body enlarged.  When he got that big I added some wooden twigs to the container holding his foliage food.  He moved over to a stick a couple days ago...

That position is quite characteristic for a caterpillar who is ready to pupate.  I had made sure that at least one of the sticks was at an angle such that he could hang beneath it using those clasping prolegs in the center of his body.

He then got busy creating a delicate silk sling to support his body, and the next morning I found him...

 ... suspended by that sling, with the prolegs and front true legs retracted from the stick.  The above photo was taken at 9 a.m..  I had chores to do that day and didn't get back to check him until nine hours later when he looked like this:

This is what boggles my mind, and why I continue to be as fascinated as a child by this process of metamorphosis.  He is forming his chrysalis, and you can already detect the wing structure in the upper green portion (slightly crimped by the sling, with little dots at the base where he will have spots on the trailing edge of his wing.)

He looks nothing like a caterpillar any more, and by the next morning, this part of the transformation is complete:

He is now the color of the stick and is reasonably camouflaged from predators for the somewhat prolonged time it will take for him to continue changing into a butterfly.  That casing around him is also relatively hard and presumably relatively resistant to ants and mites and maybe even the parasitic wasps.  It probably is also relatively impermeable so he doesn't dehydrate while he rearranges his body structures to prepare for flight.

Here is the same chrysalis at the same time, taken from the reverse angle to emphasize the silk sling.  How does he do that??!!  Make a sling that goes around behind your body like that?

Now I wait for the final step when he ecloses in butterfly form.  With Monarchs, my wife and I can tell within a couple hours when the butterfly will emerge.  But this one will be a litle tricky, because I don't have much experience with swallowtails, and it will be hard to detect color changes inside that dark chrysalis.

Stay tuned.

Update:
After about another week (on July 5), the chrysalis looked about the same -

- I use ambient light on the screen porch, not studio lighting, so it's hard to compare the photos for color, but the changes are subtle at best - perhaps more black than brown now.

Black swallowtail (Papilio polyxenes) egg

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Re the photo (taken May 30): The alert came from my wife, who yelled "Stan, black swallowtail in the garden!"  We both hustled out, and there she was, hovering near the ground seeking a suitable location for her eggs.  For years we've been raising fennel for the specific purpose of attracting black swallowtails, but it hadn't emerged yet.  She visited the big clump of parsley, then chose to oviposit on a fresh shoot of Queen Anne's Lace, a weed which we tolerate but deadhead before it can reseed itself in the fall. 

Finally, a Black Swallowtail caterpillar

This summer I seeded my plot in our local community garden with an abundance of food plants for Black Swallowtail butterflies, but my plans for raising a bunch of them were foiled by some freakish weather.  I thought this year would be a total loss in regard to Black Swallowtails.

Imagine my surprise a couple days ago when I went to the mailbox and saw this colorful fellow resting on a twig.  He/she had apparently wandered away from the clump of rue (another BST foodplant) we have planted by the mailbox.

I brought him in to a container on our screen porch, provided some rue and carrot tops, and then after two days of eating and producing frass, I found him like this this morning:

The caterpillar ignored the twigs I placed in the container and chose instead to create its mat of silk on the wall, and has suspended itself via a silken harness (which wraps behind the nonexistent "shoulders" of the cat).  The next step will be to convert that caterpillar body into a brownish pupa.

Addendum:  The chrysalis was fully formed by September 11 -

As of October 6 there have been no external apparent changes; looks like this butterfly is going to overwinter in the chrysalis.

Black Swallowtails pupating

When the Black Swallowtail caterpillars are ready to pupate, they leave the foliage of the food plants (fennel, parsley) and wander about seeking twigs on sticks. Having found a suitable one, they proceed to anchor themselves with a silk attachement at the base and a remarkable silk strand enclosing the upper thoracic region, so that the pupa is suspended like a mountain climber hanging from a cliffside in a sleeping bag. How they manage to spin a silken cord like that around their bodies is a process that I haven't been able to observe or capture on film.

For several days the caterpillar hangs like that, while undergoing some subtle color changes on the surface. Then it becomes very active with a wriggling, shimmying motion, and proceeds to shed its skin. Emerging from inside the skin is the pupa in the second image above, with the residual skin still visible at the base. Incredibly, the silken cord remains intact, supporting the creature in its new guise.

Sometimes the pupa/chrysalis remains green, but most of the ones we've had have gradually turned to a brown color as in the bottom photo; at that point they look ever so much like an excrescence on the stick itself, and that camoflage undoubtedly helps prevent predation. The caterpillars that reach this stage by late August - early September will emerge ("eclose") about two weeks later. Those that pupate later may remain inside the brown chrysalis over the winter - through temperatures of 30 below zero. Incredible. And then on a warm spring day the adult Black Swallowtail appears.

I'll have some photos of our late summer hatchlings in a day or two.

Black Swallowtail cat

The black swallowtail caterpillars have been eagerly dining on parsley and fennel for several weeks, growing fat and colorful to a degree not fully captured in this quick photo. Six of them have already formed a chrysalis (photos of those to follow later this week).

Starting a new phase of life

Here's the newest addition to our neighborhood - a gorgeous female Black Swallowtail (Papilio polyxenes).

I photographed her shortly after she eclosed from her chrysalis a couple days ago.   She began her life in an egg laid on a rue plant out by our mailbox last summer.  As a caterpillar she stayed hidden in that foliage, undergoing several molts until early autumn, when she emerged on the top of the plants, looking for a stick to pupate on.

Because there were no vertical sticks in that flowerbed, and because she was at risk of predation from local wasps, I elected to bring her (and a few of her siblings) in to our screen porch for the winter. 

As demonstrated in the photo above, she wasted no time once offered a stick, spinning a silken "sling" to suspend herself for the metamorphosis.   The photo below shows another black swallowtail caterpillar whose chrysalis is fully mature (and remarkably stick-like in appearance).  That is how she stayed from late autumn until this spring, outwardly static but changing inside.

Remember the weather this past winter?  Here is south-central Wisconsin the temperature fell below freezing on January 18, and stayed below freezing for two weeks until February 2, bottoming out at 26 below zero Fahrenheit on January 30 and 31.  During that time this lady spent her days and nights outdoors on an unheated screen porch.

Butterfly chrysalises are at risk for dehydration over the winter if they are located away from any precipitation, so I placed the terrarium in a corner where it would get snowed on.

I saw her hanging from the chrysalis last week.  She had emerged on a cloudy, cool (50s) day and she was clearly too weak to fly.   Her wings were perfectly formed, but too floppy to function aerodynamically, so I brought her inside to 70-degree temps and offered her some sugar-water (which she mostly ignored).  I returned her to the screen porch when temps warmed up, but it took one more day before her wings fully hardened and she flew away.  The photos below show the subtle sexual dimorphism of the species.  The top photo is a male who eclosed the following day, with prominent yellow spots in two rows, just a hint of blue, and then the pair of false eyespots near the tail.  Below that is the photo of this lady just before she flew off: yellow spots in the same pattern, but smaller, and the blue markedly enhanced in a pair of arcs that are sometimes hard to see because the forewings often cover part of the hindwing (she held them out for this portrait).  She also has the eyespots to lure predatory birds to her disposable rear wingtips.

Everything about this process fascinates me - the metamorphosis of course, but even moreso the remarkable resilience of a creature often portrayed as fragile and ephemeral.  The ability to fly upwind when you have the weight and shape of a Kleenex.  The adaptability to spend months as a crawling caterpillar, and then after dissolving and reshaping oneself to be able to fly away over a rooftop.  This is what fifty million years of evolution can produce.  Awesome.

Female Black Swallowtail

Almost forgot to show pictures of our last Black Swallowtail release. A handsome female (characterized by the prominent blue on the dorsum of the hindwing). We have one chrysalis remaining, which apparently is going to go dormant, overwinter with us, and eclose in the spring.

A late spring arrival (Papilio polyxenes)

Our first Black Swallowtail eclosed this week; it had spent the winter in a chrysalis in our screen porch.  On the day it emerged, a Giant Swallowtail cruised through the garden and we saw an Eastern Tiger Swallowtail up in the trees, giving us the uncommon Swallowtail Trifecta.

Eggs on Queen Anne's Lace

While I was out enjoying my walk this morning, my wife was slaving away in our garden. She weeded out some Queen Anne's lace, a plant of the carrot family which has an attractive umbel of blossoms, but which is weedy and invasive in gardens. Knowing that it is a host plant (food plant) for black swallowtails, she checked the underside of the leaves, and sure enough, there was a cluster of eggs. I've been growing bronze fennel for the sole purpose of attracting BSTs, but they seem not to have found the fennel yet.

The bottom photo shows a magnified view of the cluster of eggs; they have a shape kind of like the old-fashioned candy root beer barrels. We now have them safely stored in the house where predators won't bother them, and we'll be glad to feed the caterpillars all the Queen Anne's lace they can eat. Last year I blogged the life cycle of black swallowtails, but I'll probably do so again this year, since they are such magnificent creatures.

Addendum:  These turned out NOT to be Black Swallowtail eggs.  For the answer, see this post.

Black Swallowtail "mating avoidance flight pattern"

A couple weeks ago I was lucky enough to pick a day for a hike when huge numbers of butterflies were out.  Sulphurs had emerged from alfalfa fields by the thousands, Monarchs were migrating, Pearl Crescents were on the goldenrod, but best of all the Black Swallowtails were out in force.  I usually consider myself lucky to see one or two; that afternoon I saw over a dozen in one field.

And as I watched, I saw a phenomenon I'd never encountered before.   Mating behavior is pretty easy to spot in this species, because they are large butterflies, and there's a subtle color diffference between male and female, and they are not very territorial, so when you see a "chase" you know it's a prelude to (attempted) procreation.

That afternoon I watched a female rebuff a male by flying away from the thistle where he had approached her.  He gave chase.  Instead of flying horizontally, she started to go vertical.  Totally vertical.  She was flapping herself up and up and up and up - to I would guess over a hundred feet in the air.  He was following along right behind her.  Understand these are large, powerful fliers who can move like the wind horizontally, but the vertical ascent was much slower and more laborious.  I watched these two black specks get smaller in the sky, and then...

Then she plummeted to earth.  I don't mean that she flew down.  She fell like a rock.  It was hard to see exactly, but it appeared that she just folded her wings above her head and let gravity take her down, because I didn't see even a flutter.  The poor male was left hovering a hundred feet in the air wondering where in the hell she had gone.  I would guess his pursuit is based on pheromones rather than visuals, so her sudden descent, probably right through her previous pheromone trail, might be totally undetectable.

I didn't see this just once.  I saw it four times with at least three different groups of BSTs, so I'm confident it was a standard avoidance maneuver rather than an accident or the quirk of an individual.  Later I spoke to a friend who's much more knowledgeable about butterfly behavior than I am, and he indicated that this type of flight pattern is well recognized, and has been documented among other butterflies, some of whom use it as a predator avoidance mechanism.  He suggested that I should document this somewhere - so that's why I'm writing this blog post.

Tiger swallowtail on Shiraz lily

After I returned from my hike this morning, I was standing in the front garden when a huge swallowtail swooped down to nectar on one of our Shiraz lilies. I was only able to fire off one quick photo before he sailed away; it's a bit out of focus because a strong wind was whipping the tall lilies and the autofocus of the camera seemed to prefer the lily petals to the swallowtail wings.

Tigers tend to lay their eggs on treetops and other inaccessible places, so I've never been fortunate enough to find some eggs to raise.

(Technical note: The pale band at the trailing edge of the forewing is almost continuous. A continuous band is indicative of a Canadian Tiger Swallowtail; the Eastern Tiger Swallowtail has a band interrupted by black. We live on the margin where the territories of these two butterflies overlap, so I wonder if the one above could be a hybrid.)

Red-spotted Purple

A beautiful butterfly saddled with the dreadful scientific name Limenitis arthemis astyana. It's reasonably common because it is able to utilize a wide variety of trees (cherry, willow, aspen, poplar, birch, juneberry, basswood, hawthorn, apple) as host plants for its caterpillars.  It looks a bit like a Black Swallowtail or Pipevine Swallowtail, but of course lacks the "tail" that defines the swallowtails.

The "red-spottedness" is barely visible on the wingtips from above, but is much more apparent on the undersurface of the wings, which I was not able to photograph.  This fellow (?lady) was basking on fresh oak leaves at the Gotham Jack Pine Barrens State Natural Area last weekend (hiking path plotted on Pedometer).

I've never been successful in locating any eggs or caterpillars.  I would love to raise some because I would like to see one emerge fresh from a chrysalis.  Those wings are truly iridescent and frankly awesome in real life.  The photo enlarges with a click (and I'm currently using it for my wallpaper).

Virginia Tiger Moth (Spilosoma virginica), and the "Yellow Bears"

Last summer I posted the photo above and identified the eggs as those of the Black swallowtail, because we had  found them on Queen Anne's Lace, a  favorite food plant for the BST.  I was wrong, and never amended the post.  Time to provide followup.

Several weeks later the early instars (above) were ravenously eating, and it was obvious they were not swallowtail caterpillars.  I had no idea what they were until several more weeks had passed...

These are the classic "yellow bear" caterpillars, similar to and I think related to the even better-known "wooly bear" caterpillars.  They grew rapidly and finally began "pacing" around the container, looking for a place to pupate.

So, I put them in a shoebox which contained mulch and leaf litter, into which they could burrow.  By the end of August a couple had eclosed (one is visible on the inner surface of the box at the top left).  The others stayed in their cocoons, and decided to overwinter and await more pleasant weather before emerging.

The cocoons are difficult to see in the litter - even when you know they are there.  There's one in the mass of organic material above, on top of the big leaf and under the little leaf fragment.

Here's an easier one to see.  I've detached some of the mulch, and you can see a bit of the silk underneath.  Click this pic (and the others) for fullscreen version.

The overwintering moths began emerging at the end of May.  These are the Virginia Tiger Moths, very attractive mostly-white, fuzzy moths.

This one is perched on my finger, raising his wings to show a few of his spots.  I had hoped to move the wings to show the coloration on his abdominal segments, but when I touched him, he flew away...

Addendum: Magickcanoe has a photo of the coloration of the abdomen, and a better image of how the cat's body hairs are incorporated into the cocoon.

It's the season for Black Swallowtails

I've previously posted a series of entries documenting the life cycle of Monarch butterflies. Ours are now emerging from their chrysalises at a rate of about 5-10 per day, and will soon be heading toward Mexico.

Now the focus shifts to the Black Swallowtail. This past week the adults began ovipositing on plants in our garden. The image at the top shows a cluster of eggs on fennel, and below that are three eggs on three leaves of parsley. The bottom image is that of a not-very-attractive early instar; he/she will be much more impressive in a couple weeks. Stay tuned.