Monday, April 24, 2017

The Life History of the White Furcula




It's probably not an exaggeration to say that the majority of meat-eating animals (taking into account, not just tigers and lions, but all the parasitic wasps, birds, spiders, parasitic flies, and so on) feed primarily on caterpillars. The caterpillars didn't get a vote in this, so they have concentrated on creating millions of ploys to avoid being eaten.

For instance, some caterpillars have learned how to eat poisonous plants without themselves being poisoned. Instead they sequester the poison in their tissues, so that whatever creature tries to eat them will be poisoned. Others have venomous hairs or spines on their backs so that whatever creature mishandles them will be stung and even killed. Other caterpillars look exactly like a gooey revolting bird dropping which no one is interested in eating. Or they might get two large false eyes on their back and look so much like a snake head that a bird that suddenly spots one nearby in the leaves will fly off in fright. The commonest, of course, is just to look so much like the leaf they are sitting on that they become invisible.

Well, those are all familiar ploys. The caterpillar of the White Furcula moth provides some new ones.

First, let's straighten out some anatomical matters. A moth caterpillar is essentially a mouth  with a huge vacuum-cleaner bag behind it which it constantly stuffs with food in order to grow as fast as possible (before it becomes one of the vast majority that get eaten). If you look at the first picture above, you will see that the dark area low down where the head is (on the right) has three slender reddish pairs of legs which will be its regular legs when it converts into a moth. Behind them are four pairs of round fat elephant legs, to support its long body that trails behind the "real legs." These are prolegs, that work fine as legs, but will disappear when the caterpillar develops into a moth. Most caterpillars have these, followed by a gap, and then at the tail end, one more pair of prolegs. What has happened here is that the furcula caterpillar has converted these into two long tentacles that it normally carries behind it (see second picture), but that when approached by a predator, it can pump fluid into to extend their length almost double.

What it does then, which you must see to believe (which you will see in the next series of pictures), is, it faces the approaching predator (in this case, my finger), throws those tails up over its head, extends them as long as it can, then slaps them down on the ground in front of its head (actually making a sound you can hear from a few feet away). It has very much the appearance of a scorpion striking its venomous tail down, and a small predator might very well move away, thinking it got off with a close call.




Now that little trick, pretending to be dangerous when it is actually harmless, and constantly eating, may get the defenseless caterpillar through this perilous period of its life as fast as possible before something catches and eats it. But there is still a serious hurdle to get over. It must spend many months in a cocoon changing from larva to adult, a time when it will be even more defenseless, even more slow moving, in fact not moving at all. Now every caterpillar faces this, and there are a number of dodges they use to get through it, maybe buried underground or under the leaf litter or camouflaged as chip of wood or a dried winter leaf. The furcula does this in its own way.

As you might have noticed, the White Furcula caterpillar comes in two color phases, green like this one we photographed in the wild doing its scorpion trick, and the yellow phase we photographed at the beginning of this blog, a different individual, which we brought home with us because it looked full grown, and we thought it was close to making its cocoon, and we wanted to watch the process.

Sure enough, after about a week it flattened itself against a narrow stick which was about its own diameter and spun a thin cage around itself, thin enough that we could still see it inside busily continuing with its spinning.


After several hours it had woven enough silk around itself that the cage was now opaque, and had somehow taken on the color of the stick.


And here is how (if we had left it outside) it would have spent the winter, hiding in plain sight disguised as a little thickening around a stick. We kept ours in a jar (just in case its trick didn't work) out in the unheated garage, knowing that it needed to experience some freezing temperature in order to complete the metamorphosis pattern and emerge at the right time. It had made its cocoon August 19, 2016.

Once it warmed up in spring, we moved the jar into the house and kept it on the dining room table, so we could keep a careful eye on it. On April 21, 2017 while we ate breakfast, we checked the jar and saw a hole in the side of the cocoon.


We took the moth out on the porch that night, took some pictures of it in the twilight, then let it go. Perhaps its final ploy was to become a beautiful moth so that we would feel well rewarded for looking out for it for eight months, giving it a slightly better chance of finding a mate, getting some eggs laid, and perhaps projecting itself into the next generation.






Saturday, March 18, 2017

We have been remiss

We haven't done a blog for months. Partly it was because winter intervened, a down-time for most insects. Partly we have been busy. A publisher has shown some interest in our book of 100 common insects, but they wanted major revisions (mainly to make it a bit less conversational, and a bit more scientific), which we have now tried to do, and are waiting for their response. And an interesting job: we have been helping Game and Fish monitor a very rare bird which is spending the winter in Arkansas. We don't know if we are meant to say anything about it publicly, but we will give a full report after the species leaves the state this spring. Plus we have done a first draft of another book, Fifty Common Arkansas Spiders, which perhaps I will put a section of here shortly. And finally, we have been making regular trips to Tucson to see our grandson.

We are just now back from Tucson, so here is a report of things in the desert. When we were there in December it was surprisingly quiet in insect life (for us who naively thought everything went on all year there). On this new trip in early spring life seemed to be picking up. For instance, at our favorite Saguaro East National Park things were mostly quiet, but gorgeous fresh male Black Swallowtails had set up territories all along the trails.


Just as Falcate Orangetip butterflies come out early in the spring here in Arkansas, the Sara Orangetip comes out early in the desert, and they were fairly common in Arizona. We also saw, somewhat more special, the  "Pima" Desert Orangetip (we think).


There were other butterflies around, but not a lot, as the flowers were only just beginning to bloom. Also it seems that it is mainly male butterflies that emerge first in the spring, and they are so intent on finding females that they don't stop to nectar, which makes them very difficult to photograph.

One day we went out to Sweetwater, the city's water reprocessing plant, and it also was almost empty. In winter there are hundreds of wintering wildfowl, but now they had mostly left. I guess that's also a sign of spring. But there was at least one sign of spring right there at Sweetwater. The scruffy areas around the edges of the ponds were teeming with Round-tailed Ground Squirrels. The first one we saw aroused our sympathy, because it looked like it had a prolapsed uterus or some other disaster of childbirth. But when we looked more carefully, we saw we were actually looking at a male with a superabundance of testosterone.


A certain amount of excitement came when we visited the Tucson Botanical Garden. There were lots of butterflies flying around, especially Monarchs. And sure enough, there was a Monarch with a tag on its wing. There is a particular interest in the Monarchs of this southwestern state, as some of them winter along the Pacific Coast, and others in Southern Mexico, so it is hoped that returns on tags might straighten out some of the patterns. We took a picture of the tagged butterfly. (We have turned the picture upside-down so you can read the number on it.)


We sent our picture and reported the information to the address on the tag. After a few days we got a reply:

"Hi Norman, AK977 was tagged right here at the Tucson Botanical Gardens..."

Well, I guess that's information too.

Anyway, we weren't in Tucson to pursue science, we were there to visit our son and daughter-in-law, Gawain and Heather, and see how our grandson was progressing. In only three months he had changed a lot. He was more mobile, he was really strong, and he had an enormous smile for everyone. And the truth is, at this time of year there was more wildlife to be seen close at hand in their backyard and around their neighborhood than there was in the desert. The reason for this is in the style of gardens. They live "in town," which is to say more or less in the center of Tucson in an area of blocks of smallish houses with nice gardens. Now here in Jonesboro, most gardens consist of a lawn treated with heavy poisons from some lawn care company. One or two bushes on either side of the front door, one or two Bradford pear trees, and that's it, its own kind of barren desert (not the lush Sonoran desert of Tucson).  Because water is always an issue in a dry area, instead of poisoned lawns and pear trees in Tucson, the yards were planted more or less densely with cacti which are not only pretty to look at but draw in wildlife off the desert, particularly birds.

We spent a lot of time on their back porch around the bird feeders, and birds teemed. After our several visits we know some of the birds almost personally. There is a very tame mockingbird that deafens us when it sings near at hand, as it was doing constantly this trip. There is a very pretty vermilion flycatcher that has posts all around the house, and does little song flights. I have taken a hundred pictures of it, but it is hard to stop.


By the time we left neither the flycatcher nor the mockingbird had found a spouse yet, but they were working hard at it.

It is not just little dickey-birds that we see in their back yard. We have seen Kestrels and Peregrines, and the city of Tucson is overrun with Cooper's Hawks. We have not been on a trip without seeing several Cooper's, and at any moment one might shoot through the yard out of nowhere, scattering the birds in all directions.

  
 This trip we saw something especially good, and were so slow and rusty as birdwatchers (the insects have really stolen us away in the past ten or fifteen years) that we nearly missed it. Cheryl and I were taking the baby out in its pram for a morning walk around the six or eight blocks surrounding their house. We came around a corner, cars and people and houses on all sides, and there was a large hawk in the air over our heads. My guess is it was in migration and had spent the night in a tree there, and was just then trying to catch an early morning thermal and get on its way.

It was not very high, we had good light, we had our binoculars on it, and we were completely flummoxed.  We were looking straight up at it, and so we were seeing its underside. It was completely dark gray, with a narrow even darker gray border around its wings. The only distinctive marking was on the tail: The gray tail came out from the body, then about the middle there was a single white band that went all the way around the tail. Then it was gray again out to the end with a narrow band of white at the tip. We could not think of any hawk with these markings.

And then I did think of one, a bird I had seen at Big Bend forty years ago: A Common Black Hawk. But that was a wild guess. I couldn't actually think of a single field mark for that species, except that it was black. And I knew it was a very scarce bird (when we got back to the house and read up on them, there are only about 300 nesting pairs in the U.S.). Also, they are not found in cities, they are found in wild remote wetlands. So without better evidence than this unexpected sighting, we would have a hard time convincing ourselves that this is what we were seeing.

The bird had found its thermal and was now rapidly spiraling upward, and would soon be gone. I was carrying my close-up camera for insects. It had a 100 mm macro (for extreme close-ups) lens, my telephoto lens, regretfully, back at the house. Suddenly it occurred to me that the camera I had (100mm) was like a weak telephoto, better than nothing. The hawk was still pretty close. I changed the setting to use it for a distant shot, pointed it upward (the hawk was spiraling up higher and higher), I pressed the button, and nothing happened. I looked at the camera and realized I had forgotten to turn it on. I quickly turned it on, focused on the bird again (so high up by now it was nearly out of sight), and took one despairing shot before it disappeared. Here is the picture.


It doesn't look like it would be very helpful, but here is where you see the marvels of modern digital cameras. I downloaded it onto my computer and then magnified it as much as I possibly could, and then adjusted it to bring out as much contrast as possible. And here is the image I ended up with:


There is the single white band through the center of the tail. When we got the books out, we found that was indeed a mark on the Common Black Hawk, and there is only one other hawk with that marking, the Harris's Hawk. That would be a problem in our ID. Harris's Hawks are evidently common in Tucson, the city itself, and the Common Black Hawk would only be a great rarity in migration. So we scrutinized the two species side by side in the books. Harris's Hawk has panels of bright rufous on its wings, both above and below, and we had seen this bird in bright morning sunlight, and there was no trace of color, only the different shades of dark gray. And you can see in the picture here that the wings have a narrow border of black outlining them, something we had seen clearly and commented on, and a marking shown in the books for the Common Black Hawk, but with no such marking in the Harris's. And then we found a clincher, a mark we hadn't known about, and had not noticed when we were looking at the bird. The Common Black Hawk has what the books describe as a "comma" of white out near the tip of the wings. In the picture here, with the contrast turned way up, the white "comma" was perfectly clear (making allowance for the poorness of the picture).


Gawain looked up the Audubon site on his phone and a Common Black Hawk had been seen north-west of Tucson within the last couple of days.