Lucky days

bears, boulders, and butterflies

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One lucky day in May, I hitched a ride to Pack Creek—a lovely, smooth flight each way. As soon as we arrived, we saw a mama brown bear and a big cub, digging clams far out on the tide flats. Mama noted our presence and went right on digging. There were two solitary bears on the north edge of the tide flat, but that didn’t bother her either. Some fine bear-watching continued for an hour or more.

One other person and I set off for the trail to the tower, leaving several others out on the mudflats, still watching. Just about then, mama decided that was enough clams and began to amble back up toward the forest. Her chosen path lay between the two groups of humans, so of course those on the mudflats courteously waited until mama and cub had strolled calmly back to the shady woods. Then the mudflat people could again move toward the trailhead, finding bear beds and bear trails above the beach.

A few days later, Parks and Rec hikers headed out to Blue Mussel cabin, passing through Cowee Meadows. The timing was just right for the first wave of flowers: pink shooting stars and yellow buttercups carpeted the open areas, with lots of yellow marsh marigolds in the sloughs. Spectacular, against the backdrop of the still-somewhat-snowy mountains. There was plenty of bear sign along the trail and the beach marmots were out on the rocks.

There has been a fair amount of work on the trail from the roadside parking to the Cowee Meadow cabin, and more appears to be in the works, judging from the big canvas buckets of crushed rock that lie not far from the trail in the woods. So some of the worst rooty mudholes may be a thing of the past before long. Yay—State Parks! (Now, how about fixing the window screens in the cabin!?)

Arriving at Blue Mussel cabin, there was birthday party with apple strudel and congenial chat with a couple of visiting folks from Whitehorse. The bouldery ‘beach’ right in front of the cabin is strewn with well-worn white granite boulders—a big contrast with the darker rocks on either side. Those round, pale boulders were rafted in on glacial ice, presumably from somewhere up Lynn Canal, several thousand years ago.

When the temperatures soar above sixty-five or seventy degrees, most Juneau folks think it is hot weather.

So our walk up toward Granite Basin on a recent sunny day, with temperatures about seventy five or so, seemed really steamy. But even in that heat, lots of songbirds were singing (warblers, sparrows, kinglets).

Someone spotted a pair of harlequin ducks in the basin. The male will only stay with her until she has laid all her eggs; he will then go down to the rocky points on the shores to loaf about with other males while she incubates the clutch of eggs. When they hatch, she will escort her ducklings downstream toward the sea. Later in the season we always look for flotillas of little ducks bobbing and paddling in the rapids. But I have to wonder how they negotiate Ebner Falls! Can they just flutter down over the turbulent waterfalls and skirt around the roiling waters where the creek makes sharp bends?

margined-white-butterfly-by-bob-armstrong
Photo by Bob Armstrong

The sides of the trail were decorated with swathes of white-flowered miners’ lettuce, dark pink flowers of rosy twisted-stalk, and several kinds of violets. Numerous white butterflies known as ‘margined whites’ flitted from flower to flower. The males are a clean white with some darker veins on the wings but the females are often somewhat yellowish. One male had found a female and spent long minutes with her instead of visiting flowers. She probably will lay her eggs on plants of the mustard family, such as the cresses. However, some members of this genus (Pieris) of butterflies also use other plants as hosts, and it will take a bit more digging in the literature to find out if our margined whites have a variety of host plants. It is possible that these butterflies may have two generations per year, one in spring and another in late summer.

Nugget Dam still holds firm, as water charges over it. I found that that, as usual, dippers are nesting in the dam itself. The parents were already busily feeding chicks before Memorial Day; the rate of feeding suggested that the chicks were quite sizeable and very hungry. I spent a happy half hour just watching the parents at work.

Wrens

Big presence in a tiny package

The little brown bird that we have long called the winter wren nests in forests across northern North America and Eurasia (plus a bit in North Africa). Because it is the only wren on the other side of the Atlantic, it is called The Wren there. However, taxonomists looked more closely at this widespread species and decided it was really three distinct species: the Eurasian one, another one spread through the northern forests of North America as far west as British Columbia, and one on the Pacific coast. So now the name of Winter Wren belongs to the widespread North American populations and ‘our’ wren is called the Pacific Wren. It is one of over sixty species of wren, all living in the Americas except for the single species in Eurasia.

We notice wrens as they flit about in the forest understory or sing from atop a snag or rootwad. The long musical song is a favorite for many of us. Males sing to establish territories and attract females. Territory size ranges from about two to ten acres in our area and the literature reports that males may hold their territories all year round. Wrens are not typically migratory in our area, according to the literature, although those that nest at higher elevations may move downhill in winter. They conserve body heat in cold weather by roosting together, sometimes over a dozen birds at once, in old nests and other cavities. Nevertheless, severe winters are hard on them and wren populations sometimes decline drastically as a result.

Wren diets consist almost entirely of insects and spiders, all year long. They and other songbirds sometimes pick fly maggots from salmon carcasses. Because wrens are so small, maintaining normal metabolism requires lots of food, relative to their body size. The literature reports that very occasionally, or in certain locations, wrens might eat berries, small fish, snails, small crustaceans such as amphipods.

 

winter-wren-at-tree-hole-nest-by-bob-armstrong
Photo by Bob Armstrong

Males build several nests, often a mossy ball but sometimes in a cavity in a log, stump, or earthen bank. Visiting females inspect each nest before deciding to stay with a particular male and selecting a nest for her eggs. If a female decides to stay, she modifies the selected nest a bit just before she lays, adding to the lining and often building a little lip at the entrance. In the Juneau area and elsewhere, polygyny is quite common: around Juneau, forty-four percent of males mated with two females or rarely even three.

A female usually lays about five to seven eggs and incubates them by herself, taking a little time off to forage. Incubation lasts about sixteen days, and it takes another seventeen days or so for the chicks to leave the nest. Two broods per season may be possible, and if the first nest fails, females commonly re-nest. When the chicks hatch, males usually help feed them, but the amount of help he provides is reported to vary considerably. I could find no information on the relative amount of help that polygynous males of this species provide to their first and second mates, but in the related marsh wren, the male’s role varies with the productivity of the marsh, while in blackbirds, males commonly favor their first females.

In the 1990s, we studied nesting wrens in the Juneau area. Juneau wrens had relatively high nesting success: over seventy percent of nests (sample size, n = 143 nests) produced fledglings; that is higher than in most other studies. Cavity nesters such as wrens commonly have higher nesting success than open-cup nesters; as an extreme case, red-breasted sapsuckers in Juneau were all successful (n = 31). For comparison with open-cup nesters: robin nests were 31% successful (n=30), hermit thrushes 36% (n= 36), fox sparrows 27% (n= 126), Wilson’s warbler 42% (n = 27).

Most nest failures were caused by predation on eggs or chicks. Red squirrels and Steller’s jays are among the likely nest predators, both of which we have recorded to eat eggs and chicks. Other possible predators include crows, ravens, mice and shrews, flying squirrels, weasels, and marten. Adults may be prey to sharp-shinned hawks, falcons, and marten, among others. Decades ago (mostly in the 1930s and 1940s) red squirrels or marten were introduced to several islands of Southeast Alaska, and their populations flourished; this very likely has had serious consequences for the populations of wrens and other songbirds, as well as grouse and ptarmigan.

The oldest wren on record was about six years old, but most don’t live anywhere near that long. Estimates of annual survivorship of adults (in English populations of The Wren) ranged between about thirty to about sixty percent. So if, for example, we take a middle value (i.e., 45%) and start with 100 adult birds, the next year there would be about 45 birds, and the year after that about 20 birds, and then only 9 birds, and so on. Thus, few adults would get more than one or two breeding seasons. Of course, juvenile survivorship would be much lower, and each hatchling would have a low probability of surviving to breeding age.

Although wrens nest in a good variety of forest types, they typically reach their highest densities in old-growth forests or mature forests with a good understory. Very young forests and second-growth forests generally do not provide a good understory for foraging and nesting, so those conditions are not favorable for wrens in most cases. Any kind of logging is generally detrimental to their populations, but large clearcuts and serious forest fragmentation are especially bad for wrens.

Anadromous fish in Dredge Creek

In praise of beavers

Dredge Creek begins in a long pond near the Glacier Spur highway, crosses under the road, and flows below the slopes of Thunder Mountain. It crosses the highway again and goes through a series of beaver dams to Dredge Lake in the Mendenhall Glacier Rec Area. It then passes down a channelized ditch, through some more beaver dams, to the Holding Pond. From there, creek water flows out through a concrete structure (formerly used for counting fish as they moved in and out of the creek system) to the Mendenhall River. Into another side of the Holding Pond flows the outlet of Moose Lake, passing through two beaver dams on the way.

Cutthroat trout and Dolly Varden can sometimes overwinter in the Dredge Creek system and spawn there in the following year. Coho salmon come in the fall to spawn, especially in the upper reaches of the creek. A few coho may spawn near upwellings in Moose Lake too

The Dredge Creek system is small (the creek is only about a mile long), but it is a popular spot for local fly-fishers. Bird-watchers can find some unusual species such as redstarts there, in summer, and photographers can get good photos of migrating swans and ringneck ducks, for example. Wildlife-watchers and photographers can sometimes see herons, bears, mink, and otters there (to name just a few worth watching).

The beaver dams cause concern for some people, because trails are occasionally flooded by backed-up water and because the dams might block the movements of fish in the system. For over seven years, a group of volunteers, known as the Beaver Patrol (a registered nonprofit organization), has monitored this system to reduce trail flooding and assure fish passage. This group works two mornings a week from spring through fall (usually April into December), opening notches in dams or sometimes removing dams entirely, as needed.

With the cooperation of the Forest Service, the Patrol has also installed several devices that deter beavers from filling culverts. By trial and error, the Patrol has found that different kinds of devices work better in certain situations—one size does not fit all. Unfortunately, some of these devices have been subject to periodic vandalism by persons who do not understand how they are helpful in managing water flow.

Because the area drained by the creek is quite flat and this is ‘rain country’, it sometimes happens that a big rain event occurs between the Patrol’s workdays and trails get flooded for a couple of days. One workday suffices to bring the water levels down again (unless, of course, there is another big rain!), so existing trails are not usually flooded for more than a day or two. Raising some of the trailbeds with additional gravel (an inexpensive process) would reduce the problem still more.

heron-and-dolly-bob-armstrong
A heron catches a Dolly Varden in a Dredge system beaver pond. Photo by Bob Armstrong

Although beaver dams sometimes can be capable of blocking passage of adult fish, opening dams twice a week allows fish passage. In any unmanaged, natural system that has beaver dams, fish often have to wait for days, until high water allows them to pass over or swim around a dam. So if incoming Dredge Creek salmon have to wait a day or two, it is not a problem. Furthermore, if there is a fairly deep pool below a dam, coho are perfectly capable of leaping up and over (they are excellent leapers!). Capable observers have found that many dozens of coho have been able to pass the dams and get to the upper reaches of the little creek to spawn each year.

In the Dredge Creek area, concerned but uninformed people (not part of the Patrol) sometimes remove a small dam that is actually being helpful to fish passage. For instance, where Moose Lake enters the Holding Pond, two tiny dams help raise the water level sufficiently that the culvert just upstream is not ‘perched’ above the pool—meaning that the water level is high enough that fish can readily enter the culvert to get into Moose Lake. In this case, the Patrol tries to maintain the tiny dams to keep open the passage between the Holding Pond and Moose Lake; sometimes the Patrol has to rebuild the small dams to repair what other people have removed.

In addition to passage of adult fish, management of water flow through the dams allows movements of juvenile fish within the system or out to sea. Young coho stay in fresh water for a year or two after the eggs hatch. They often move about, from pool to pool, up and down the creek. They can weave their way through a beaver dam, or wait for high water, but the Patrol’s activity in notching dams surely facilitates the passage of juveniles.

So why not just rip out all the dams and have done? Because the scientific literature shows that beaver ponds provide really good rearing habitat for juvenile salmon. In the Taku system, for instance, both coho and sockeye juveniles grew better and survived better in beaver ponds than in other types of habitat. The literature also reports that the availability of good rearing habitat is often the factor that limits coho populations. This means that if rearing habitat is reduced, as by the removal of beaver dams, the size of the coho run in that system will probably be reduced.

The beavers in the Dredge Creek system are therefore providing a service to the fish populations, and thus to the fly-fishers and wildlife-watchers. The Patrol’s volunteer efforts in this system have had a lot of success over the past seven years: fish passage is assured, trail flooding is reduced, and the beavers and other wildlife have good habitat. Educational opportunities abound and school classes sometimes visit. And many trail walkers in the area have greeted the working Patrol with thanks. Is the effort perfect? No, because the weather changes, beavers move around, and because of the activities of a few uninformed folks who may be trying to be helpful but actually are detrimental. There is no perfect solution to balancing the needs of trail walkers, fish, and wildlife. But for the past seven years, because of the volunteer efforts, trail flooding has been reduced, fish passage and rearing habitat have been maintained, and wildlife has prospered.

The Ballet of the Unhatched Chicks

A not-so-preposterous notion

In April I listened with pleasure to the Taku Winds’ performance of Moussorgsky’s Pictures at an Exhibition. One of the ‘pictures’ illustrated in music is called (in English) the Ballet of the Unhatched Chicks. At first glance, that would seem to a preposterous notion—chick dancing inside their eggs!?

Although I don’t know what Moussorgsky envisioned, and the actual picture that may have prompted the musical image was perhaps a cartoon, it is not as preposterous as it may seem. When a chick has used up the yolk inside its egg and now fills up its eggshell, it starts to move around, shifting into position for breaking out of the shell. Then the chick punctures the membrane that creates an air chamber at the blunt end of the egg and starts pecking at the shell itself. As it pecks, it rotates (reportedly counterclockwise) by shoving with its legs. The process of pecking and shoving takes a day or two. With the help of a temporary ‘egg tooth’ on its bill and a special, temporary hatching muscle on its neck, the chick eventually hacks open the egg shell and emerges into the larger world of its nest. Sometimes assisted by a parent bird, it is a very functional ballet!

Incubating parent birds may also ‘talk’ to their eggs, as the eggs approach hatching time. In at least one case, the unhatched chicks learn these parental calls. A detailed study in Australia (yes, far from Alaska, but a very thought-provoking study) with superb fairy-wrens is a fascinating and complex example.

Superb fairy-wrens live in scrubby habitats in southeastern Australia. They are subject to brood parasitism by a species of bronze-cuckoo, which lays its eggs in nests of this fairy-wren, leaving the host birds to rear the cuckoo chicks. The fairy-wrens pay a high cost if there is a cuckoo chick in their nest: the cuckoo chick eventually evicts all the fairy-wren chicks!

So it is advantageous for the fairy-wrens to recognize their own chicks, discriminating them from cuckoo chicks. Female fairy-wrens have a special incubation call, and they talk to their embryonic chicks in the eggs. The chicks learn this call; the more often they hear it, the better they learn it. They use this call after they hatch, when they beg food from a parent. Chicks that use the ‘password” are fed more often than those that don’t. In contrast, cuckoo chicks apparently do not learn this call, making it relatively easy for host parents to tell their own offspring from an interloper. When the host parents don’t hear the right password from chicks in the nest, they can simply abandon the whole brood, which would include a cuckoo chick (and soon consist only of a cuckoo chick). Then the parents can start over with a new nest, hoping not to be parasitized again.

However, there is a price to pay for a frequent incubation call: predators hear it and often raid the nest. So female superb fairy-wrens use the call most frequently when the risk of cuckoo parasitism is high, and apparently that risk varies considerably from year to year. Thus, in some years, the risk of brood parasitism is high enough to outweigh the risk of predation, while in other years, the reverse is true.

I would not be surprised to learn that embryos of other species are capable of selectively learning certain calls and even behaviors. A fascinating area of research!

Footloose

Explorations high and low

Here is a selection of recent observations:

We took the old way up to Cropley Lake, through the woods, working our way around or over windthrows and mudholes. The sun blazed out of a blue sky, raising temperatures into the mid to high seventies—very hot indeed, by Juneau standards! Once in the big meadows near the lake, it was time for tea and lunch in the shade. On the far side of the lake, we found a wolf scat with snowshoe hare fur and bones, and the coltsfoot was already in bloom. One remnant snow patch posed no problems, but the ground was quite squishy in many places.

Three-leaf goldthread was the most common wildflower in bloom. Its flowers are totally unlike those of the closely-related fern-leaf goldthread; only the fruiting capsules show that they are related. The flowers of the three-leaf species offer nectar to visiting gnats in five tiny golden trumpets encircled by five round white petals; the other species has neither the trumpets nor the white petals. One small area held a wildflower garden of white three-leaf goldthread, pink bog blueberry, pink bog rosemary, and a single white cloudberry.

On another day near Eaglecrest, a white-crowned sparrow and a junco foraged close together in a ditch with running water. Both birds were fly-catching—jumping up to nab some tiny insects. Their stout, conical bills are not adapted specifically for fly-catching but rather for cracking seeds. Nevertheless, these birds catch a lot of bugs, especially in spring and summer and feed their chicks on bugs, too; that conical bill works quite well for bug-catching.

marmots-in-snow-armstrong
Photo by Bob Armstrong

A trip up Gold Ridge above the tram crossed several snow patches and the upper reaches were still very snowy. So midway along, we settled for watching two marmots near the snowy entrance of their den. Both sprawled in the sun for long minutes, one on snow, one on grass, barely moving except to scratch. Finally they ambled off into the brush, one of them nibbling on salmonberry leaves. Nearby, a willow ptarmigan clucked at us, cast a wary eye over its shoulder, and took refuge under some small confers, still clucking. All the while, male fox sparrows sang, advertising their territories.

A weekend in early May brought some of the lowest tides of the year, so of course I couldn’t miss that. There were lots of sea stars and sea cucumbers and other of the usual things, but I saw my first rose star, all prickly and mottled red, pink, and white. We found a big Neptunea whelk laying its spiral coil of egg cases. I saw the tiniest hermit crab I’ve ever seen—living in a periwinkle shell about three millimeters wide; while we watched, it waved its delicate wee pincers, as if to say Move on! We found one of the spectacular red hermit crabs too. On a previous excursion, we had found several of them living in Neptunea whelk shells; this one was trying to fit its rather hefty rear end into a Neptunea shell that seemed to be too small. We left it to the struggle, wondering if sufficiently large snail shells are hard to find.

Out on the sand flats at Eagle Beach State Park, there were several bear-dug pits with clumps of rice root (or chocolate lily) left behind, so it was hard to guess what the bear was after. Several large scat piles showed that he had eaten well, quite recently. This is reported to be a good-sized beast, known as Big Head to the amiable fellows that work there.

I was very pleased to see a colorful butterfly sunning itself on the sand, tilting to and fro when buffeted slightly by the breeze. This was a Milbert’s tortoiseshell, known for its sun-basking behavior. It is not common here, so this was a treat. In contrast to the colorful upper side of the wings, the underside is also beautiful but in subtle browns in a camouflaging pattern, so when the wings are folded, the butterfly looks like dead leaves or bark. It winters as an adult (as does the mourning cloak), sometimes in small groups. They feed on flowers, no doubt effecting some pollination, but also on tree sap and rotten fruits. The spiny larvae feed on stinging nettles; young larvae feed in groups inside a web on the underside of a leaf, but older larvae are solitary, sheltering inside folded leaves tied with silk. We could use a few more of those larvae on couple of local trailsides, where bare knees are at risk.

Here and there

Sundews and sandlance, willow roses and more

The lower muskegs at Eaglecrest were dotted with pink flowers of bog rosemary and the white flowers of cloudberry. Searching specifically for sundews (insect-eating plants), we found plenty of the round-leafed species just peeping up through the mosses. The long-leafed species, which we usually find in somewhat less mossy, more muddy, spots near the ponds, were much harder to find than usual. The few we did find had barely expanded leaves hardly wider than their supporting stems. And most of them were under water from recent rains; we wondered how long they could survive that way. A few days later, the water had subsided and they were still there, with leaves slightly larger and putting up what looked like a flowering shoot. OK, good, but why are there so few of them this year? We also wanted to know if the very small, young leaves could catch gnat-sized insect prey, or if the plant waits to go ‘hunting’ until the leaves are bigger and they can catch larger prey.

Wandering along a beach on Douglas Island at a moderately low tide, we noticed a group of crows strutting over the sand flats. A closer look revealed lots of small pits in the sand, several inches deep. Aha! Maybe if we watch, we will see the crows in action. Pretty soon, we saw several of them digging—and coming up with sand lance in the bill. Both crows and gulls dig up sand lance from their refuges under the sand, but on this day, the gulls were more interested in trying to steal the fish from the crows than in digging up prey for themselves. Crows that successfully retained their catches flew off, perhaps to eat in peace or to cache them for a later meal, or even to feed early broods of chicks

willow-gall-with-catkins-by-bob-armstrong
Photo by Bob Armstrong

There is a myth that ‘willow roses’, which are rosette galls induced when a midge lays an egg on the tip of a twig, occur only on Barclay willow. So some folks try to use the presence of a rosette gall to identify the willow species. But no, the very same species of midge can induce this gall on Sitka willow too, and perhaps some others. When the midge lays its egg, growth of the shoot is stunted, but leaves continue to form, so they end up forming a compact rosette cluster of crowded leaves. In the middle of that rosette, the midge egg hatches into a larva that feeds on the inside of the gall, emerging as an adult midge the next spring. The afflicted twig usually dies.

This spring I noticed some leaves of the pink wintergreen plants that were standing up vertically and looked orange, quite a contrast to the usual green. The undersides of these leaves were covered with dense arrays of orange dots. These turn out to be a rust fungus. In our area, at least two wintergreen species (pink wintergreen, Pyrola asarifolia, and ‘single delight’, Moneses uniflora) are the alternate hosts for two species of rust whose primary host is spruce cones. Called the ‘spruce cone rusts’, they reduce spruce seed viability and can deform the cone. In British Columbia in some years, nearly an entire spruce seed crop was destroyed, but I have not found any indication of such concern for Southeast. There seems to be little negative effect on the wintergreens, in part because the infection occurs on the older leaves. However, the rust infection does cause the wintergreen leaves to stand more vertically; this facilitates dispersal of spores by a passing breeze and attraction of insects that might transmit the spores to the cones.

The life cycle of the rusts is apparently regulated by environmental factors such as temperature and moisture. When the spores from the wintergreens land on the cones and germinate, sexual reproduction takes place among the new fungal filaments, and a new set of spores gets dispersed to the wintergreens, and the orange dots develop. (Thanks to Dr. Robin Mulvey, Forestry Sciences Lab, for helpful information.)

Spring things are happening quickly. Several warm, sunny days followed by showers made the leaves of cottonwood and alder leaves pop out, cheerfully bright against the somber background of spruce and hemlock. New spruce tips add to the contrast with the old conifer needles. And I finally heard my first olive-sided flycatcher of the year, shouting his “Quick, three beers!” from the edge of a muskeg on the Dan Moller trail.

Woolly bears and moths

Remarkable talents of some engaging insects

The woolly mammoths are long gone, but woolly bears are still with us. They are common up north and have been seen in Juneau too. They are so interesting, I just wanted to share with readers just some of the amazing things they do.

Woolly bears are the fuzzy caterpillars of tiger moths and some of their relatives. There are thousands of species of tiger moths in the world, exhibiting an astounding array of color, both as adult moths and as caterpillars. Although some adults show the quiet browns and grays that we commonly associate with moths, many tiger moths are arrayed in bold patterns of black and white or gaudy red, orange, yellow, and blue. The fuzzy caterpillars are equally varied.

The striking colors serve as warnings to would-be predators that the caterpillar or adult moth is distasteful or poisonous. When a caterpillar chews the leaves of its food plant, it sequesters defensive chemicals from the plant that render it unpalatable, and predators learn to avoid the warning colors. In addition, adults of some species suck up plant juices that contain particular alkaloids (or sometimes other chemicals, such as cardenolides) that have a defensive function, for both the plant and the moth.

But it doesn’t stop there—in some species, these defensive compounds can also be used as mate-attractants and in courtship. For example, in one North American species, the defensive chemicals collected by the caterpillar are converted into sexual pheromones (hormone-like chemicals, usually volatile, that often work at some distance from the animal that produces them). Female caterpillars exude pheromones to call in males. As a male approaches a calling female, he expands special organs from his abdomen, waving them around and eventually brushing them against the female, transferring to her his own pheromones. Females can detect the male pheromones and use them to help choose the best mate. Choosing the right male is important, because the defensive compounds are transferred to the female during copulation, and females then use these compounds to defend themselves and their eggs. Males that did not consume the necessary alkaloids as caterpillars were smaller and possess less of the critical defensive compounds, and females avoid mating with these lesser males.

In the Lower Forty-eight, tiger moths can have several generations per year, going from egg to adult to egg again, several times. At higher latitudes, with shorter growing seasons, there are fewer generations per year. In the Far North, a woolly bear that is related to tiger moths takes this latitudinal trend the next step: it overwinters as a caterpillar, under rocks or plant debris. And not just one winter! These caterpillars are known to spend up to fourteen winters–and that many freeze-thaw cycles– before transforming into adults. It can take that many short summers to get food enough to allow it to reach mature size.

It has long been known that many kinds of adult moths can hear—they can detect the ultrasonic calls of an approaching bat that is zeroing in on a possible snack. When some kinds of moths hear an incoming bat, they take evasive action, dodging and dropping suddenly to elude pursuit. Tiger moths detect the high frequencies too, but instead of flying erratically, they talk back! And they talk in ultrasound, made by a ‘clicker’ on the thorax. Some researchers have suggested that talking-back is a way of jamming the bat’s transmission. But increasing evidence indicates that the back-talk may be a warning that the bat’s intended prey is unpalatable and not worth chasing. So, in addition to visual warning signals that work in the light, there may be auditory warning signals that work in the dark.

Less well-publicized is the fact that the caterpillars can hear too. Some of those fuzzy hairs detect vibrations—specifically the low frequency vibrations made by the wings of a wasp that could attack the caterpillar, either to take the caterpillar back to its own larvae or to lay a parasitic egg on the caterpillar. In either case, the caterpillar would be dead. However, what the caterpillar does in response to detecting a wasp is not recorded.

I should also mention, albeit in passing, that some tiger moths use acoustic signaling in courtship, in addition to or, in some cases, instead of pheromones. This is a lively arena for intense research.

A common species of woolly bear is the larva of the Isabella moth, a rather plain, yellowish moth that is widespread in North America. The caterpillar has broad orange and black bands around its body. Folklore says that the width of the bands predicts the severity of the coming winter—but there are contradictory stories! Some say narrow orange bands indicate a severe winter, while others say that wide orange bands do so. In any case, even within a single brood of caterpillars, there is much variation, and band widths may also change with age. So, winter weather forecasting should probably be based on more scientific information.

woolly-bear-caterpillar-by-lynn-armstrong
Photo by Lynn Armstrong

The black-and-orange-banded caterpillars are so common in some places that they are known to most of the people in the community. They are so popular that towns in at least four states stage annual festivals featuring these woolly bears, complete with caterpillar races and costume competitions.

Woolly bears have it all: popularity among kids and townsfolks, fascination among scientists.