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Animal Architecture

The Architecture of a Bald-faced Hornet Nest

11-29-17 hornet nest 049A8063The exterior of a Bald-faced Hornet nest consists of an outer envelope of paper that is made up of a myriad of horizonal stripes of chewed up wood fibers that have been mixed with hornet saliva. Each stripe represents a single hornet’s contribution. The different colors represent different sources of wood. This outer envelope is only one of several (up to 12 or more) that serve to insulate the innermost, active part of the nest.

Inside these outer sheets are three or four horizontal tiers of hexagonal cells in which eggs are laid and brood are raised. Access from one level to another is at the periphery of the tiers, just inside the shell. The queen begins the nest, building a few cells and raising female workers that then take over the cell-building while the queen continues to lay eggs. As the number of hornets increases, so does the number of cells they build, and as a result the tiers become wider and wider. When space runs out, the hornets remove one or more of the innermost layers of insulating paper that form the envelope, while constructing new sheets on the outside. The nest continues to grow in this fashion until the queen’s egg-laying slows down at the end of the season.

The construction of these tiers of cells takes place upside down in total darkness, which is, in itself, quite a feat. When they are constructing a cell, the hornets keep one antenna inside the cell and the other on the outside. By monitoring the distance between the two antennae tips they can judge thickness of the wall. They do a similar thing with their mandibles, with one on each side of the wall, in order to straighten the cell walls and squeeze the pulp flat to remove water.

If the cells were built sideways or upwards they would require constant attention from the hornets until they dried in order to prevent them from sagging. Given that the cells are downward-facing, one might wonder why the hornet larvae don’t fall out. Water has a great affinity for uncoated paper (think of paper towels sucking up water against the pull of gravity). Because the larvae are damp, they actually stick to the paper cell walls. When they are ready to pupate, they must separate from the walls. They do this by attaching themselves to the cell with silk and then spin a silk cocoon.

In order to fully appreciate the intricate architecture of a Bald-faced Hornet nest, you must dissect one (they are only used for one season). Just be sure to wait until there have been a number of hard frosts, in order to assure that there are no residents. (Photo: Bald-faced Hornet nest – (left) envelope consisting of 12 layers & (right) cluster of cells it surrounded; inset:  dissected inner section showing four tiers of cells)


A Beaver’s Winter Quarters

2-1-17-beaver-lodge-interior-img_4899What exactly is it like inside an active beaver lodge in winter? It’s dark, damp and around 32°F. The living chamber inside usually has a ceiling no more than two feet high with a diameter of 4 to 6 feet, depending on the number of individuals in the family. (A typical beaver family is composed of an adult male and female, 2 to 3 yearlings, and 2- 4 kits that were born in the spring.) Fresh air enters and carbon dioxide leaves through a central vent (where mud is not applied) and through small holes that remain under logs on the side of the lodge. When there isn’t much snow and the outside air falls well below zero, the temperature inside may drop to a degree or two below freezing, but if the sun is out, it warms right back up again during the day.

The dampness is due to the beavers’ repeated need to enter the water both to retrieve sticks from their nearby food supply pile and to defecate. Upon returning to the lodge, the humidity inside increases due to the water draining from the beavers’ fur. No small wonder that if a January thaw permits, beavers will exit their pond for some fresh air, food and a little bit of sunshine.

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Bird Nests Visible

11-25-14 black-throated blue nest  043When leaves start falling from deciduous trees, bird nests appear out of nowhere. Most songbirds abandon their nest after raising one brood, never to return to it. An empty nest sits where it was built until the elements break it down, another animal recycles the material from which it was made, or a mouse takes over winter occupancy. The period of time after the leaves fall and before winter and other creatures deconstruct the nests is ideal for discovering who raised their young under your nose this past summer.

Just as each species of bird has its own distinctive song, each species also builds a unique nest. It is often possible to determine what species built a nest without ever setting eyes on the bird. The size, shape, material used and habitat in which a nest is built are remarkably similar for all birds of a given species. Eastern phoebe nests mainly consist of mud covered with moss. Gray catbirds incorporate grape vine into their nests, and line them with rootlets. Ovenbird nests are on the ground, roofed over like old-fashioned ovens. While federal permits are necessary to collect these nests, they can be admired and identified without a permit. (Photo: the combination of this nest’s size (3” outer diameter), location (3’ off the ground) and material used (yellow birch bark strips, grasses, cocoons and black rootlet lining) pinpoint the builder as a Black-throated Blue Warbler.)

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A Variety of Beaver Lodge Designs

10-20-14 beaver bank den 080Beavers are hard at work refurbishing their mud and stick lodges in preparation for the coming winter, when their movements will be restricted and they will spend both days and nights inside their lodge. When we think of a beaver lodge, we picture it in the middle of a beaver pond. This was not always the case, however, and still isn’t today. The earliest and most primitive beaver lodges consisted of a burrow in the side of a high bank with the entrance under water (see exposed bank lodge entrance in photo insert). The next advance was the addition of sticks and mud piled over the top of the bank as added protection from predators (see photo). Eventually beavers started building a complete lodge on top of the bank which had an underwater entrance. The most advanced design is the lodge we most commonly associate with beavers — one that is built up from the bottom of the pond and is completely surrounded by water. It requires the greatest amount of work but offers the greatest amount of protection to the beaver.

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Signs Of An Active Beaver Pond

4-7-14  floating beaver logs IMG_0159Beaver ponds have finally started to melt, making it easy to determine whether or not there have been beavers living in any existing lodges over the winter. The tell-tale sign is floating de-barked sticks and branches. During the winter, beavers leave their lodge and swim out to their underwater food supply pile and haul branches back into the lodge where they chew them into foot-long pieces for easy handling. The bark is removed and eaten as the beaver holds the stick and turns it, much as we consume corn on the cob. When little or no bark remains, the stick is discarded out in the open water. These sticks remain hidden underneath the ice on the surface of the water until warm weather arrives and the ice begins to melt. At this point the sticks and branches become visible, and often extend several feet out from the lodge. These sticks will not go to waste, but will be used for dam and lodge repairs. (Photo taken standing on lodge.)

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A New Book for Budding Naturalists

COVER-BeaversBusyIs there a youngster in your life who might love his or her own book about beavers? My third children’s nature book, The Beavers’ Busy Year, has just been released. Having been an ardent admirer of this rodent for many, many years, it is gratifying to have had a chance to instill a love for beavers in youngsters age 3-8 with this non-fiction book. The adaptations of beavers’ noses, eyes, ears, fur, feet and tails are highlighted in the text and photographs take the reader through the seasons of the year from a beaver’s perspective. Activities at the end of the book engage children in matching photographs of various beaver signs such as tracks, scent mounds and incisor marks with written descriptions. There are also activity/informational sections on beaver tails, beavers as engineers and creators of habitat for other wildlife, and dam building. It should be available at your local bookstore, but if not, I’d greatly appreciate your letting them know about it. Thank you!


Winter Mouse House

2-5-14 mouse nest with insulation roof IMG_4629White-footed Mice and Deer Mice are known for their keen ability to recognize a potential winter home when they see it. Abandoned bird nests provide firm foundations, and more often than not, mice will create an insulated roof made out of thistle down or milkweed fluff when renovating a nest. There are exceptions to this rule, however. If you look closely you’ll see that the roof of this nest has a slightly greenish tint, the reason being that the roofing material selected was none other than green insulation “borrowed” from a nearby human dwelling. (Thanks to Heidi Marcotte and Tom Wetmore for photo op.)

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Beaver Breath

12-2-13 beaver breath  074It’s very subtle, but in winter, especially when it is very cold outside, there is a way to tell if a beaver lodge is occupied. The temperature inside the lodge remains relatively stable at around 34 degrees Fahrenheit. When snow falls, it provides added insulation, raising the interior temperature of the lodge slightly. A layer of fat and thick fur keep beavers warmer than the air inside the lodge, plus they raise their body temperature even more by sleeping piled on top of one another. All the moist, warm air that beavers give off through breathing and evaporation escapes through the (mudless) vent that goes up through the center of the roof of the lodge to its apex. The vent’s purpose is the exchange of air; when the warm air inside the lodge rises and hits the cold air outside the lodge, it condenses and forms water vapor that is visible, indicating that there is life inside.

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Cecropia Moths Pupating

11-11-13 cecropia cocoon dissected  056Our largest North American native moth, the Cecropia Moth, Hyalophora cecropia, spends the winter as a pupa inside a cleverly-crafted 3” – 4”-long shelter, or cocoon, which it creates and attaches lengthwise to a branch while still in its larval stage. The Cecropia caterpillar, with the silk glands located near its mouthparts, spins not one, but two silk cases, one inside the other. In between the two cases, it spins many loose strands of very soft silk, presumably to enhance the insulating properties of the cocoon. Inside the inner case, the caterpillar splits its skin and transforms into a pupa. Come spring, an adult moth will emerge from the pupal case and exit the cocoon through one end which was intentionally spun more loosely, allowing the moth to crawl out the somewhat flexible tip. (Note: dissected cocoon was not viable.)

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Ribbed Pine Borer’s Winter Pupal Chamber

11-6-13  ribbed pine borer winter shelter 132The larva of the Ribbed Pine Borer, Rhagium inquisitor, (a beetle) lives just under the inside of a pine tree’s bark. It is a long-horned beetle, and in the fall, when it’s ready to pupate, it creates an oval cell by chewing a relatively flat chamber approximately 1 ¼” long. The Ribbed Pine Borer uses the woody fibers it chewed to form a raised “wall” surrounding the chamber. It then pupates inside the wall, and overwinters in the chamber as an adult beetle, emerging to mate in the spring. (Thanks to Kitty Stanley for photo op.)

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Red-eyed Vireo Nest

10-31-13 red-eyed vireo nest  033 Abandoned bird nests are evident now that leaves have fallen off the trees. Consider the time and effort that goes into the construction of one of these single-use nurseries. Take the Red-eyed Vireo’s nest you see here lying on the forest floor. The female selects a nesting site — a time-consuming task, as the requirements are that it conceal the nest and provide shade for her young. (Too much sun will cause her to abandon the nest. One female who had selected a sunny spot was observed pulling nearby green foliage over her nest and fastening it in place with spider webs.) The female vireo then collects nesting material for the three layers of her nest: Exterior – tree bark, spider-egg cases, wasp-nest paper, lichen, green leaves and pine needles. (Nests exposed to sunlight may be decorated with light-colored tree bark such as birch bark.) Interior – bark strips and plant fibers. Inner lining – grasses, pine needles, plant fibers and animal hair. She then weaves these materials into a cup-shaped nest that is suspended from a forked branch by its rim. A trip for materials is made every 3 – 11 minutes and roughly twenty seconds is spent working each load into the nest structure. This intensive work takes the female vireo approximately five days – all accomplished without the aid of any hands or tools, and she only uses the result of all this work once. Fortunately, recyclers make good use of her efforts.

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Mice Preparing for Winter

10-25-13 mouse larder 012Animals that remain active in New England throughout the year often make preparations for the colder months, when food is much scarcer. Eastern Chipmunks store up to half a bushel of nuts and seeds in their underground tunnels, Red Squirrels hang mushrooms and apples out to dry and White-footed and Deer Mice create larders, often out of abandoned bird nests. Once their young have fledged, most songbirds never re-use their nest. Mice find these empty cup-shaped containers perfect for storing seeds that they collect in the fall. The mouse that took over this Northern Cardinal nest (located in a rose bush) didn’t have to go far to collect a sizeable number of rose hips. One hopes that this isn’t this particular mouse’s only cached food, as most of the seeds (within the fleshy red covering) have been devoured. (Thanks to Marian Marrin for photo op.)

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Some Spiderlings Hatch in the Fall

antmiimic spider egg case 013Have you recently noticed a roundish, flat, papery, 1/4-inch diameter, metallic-looking structure adhering to the top of a rock? If it has tiny bumps in the center, chances are good that it’s a spider egg sac, most likely that of an antmimic spider (spiders resembling ants that often prey on ants), specifically one in the genus Castianeira. One would assume that the contents of the sac that were causing the bumps were eggs that were going to overwinter and hatch once warm weather arrives. This is true for a majority of spider egg sacs, but some, including those of Black-and-Yellow Argiopes and antmimic spiders, hold spiderlings that have already hatched and will remain in the sac throughout the winter. As long as the temperature stays cold, the spiderlings will be safe and secure until spring. If we have periods of cold interspersed with periods of warmer temperatures, or an exceptionally warm winter, the spiderlings will become active when the thermometer rises, and, not having any insects to eat, will be forced to devour each other.

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Beavers Gathering & Storing Winter Food Supply

10-15-13  beaver winter food supply pile 292(Part 3 of 3 Beaver posts)
In the fall, beavers spend weeks cutting, transporting and piling sticks and branches whose bark, twigs and leaves will hopefully provide them with sustenance through the winter. With no access to land once ice forms, beavers rely on the food that they have had the foresight to store on the bottom of the pond in the fall, as close to the main entrance to their lodge as possible. Initially the beavers dive down and stick the butt end of the branches into the mud. Once anchored, these branches form the base of a growing pile which often sticks out above the surface of the pond. (The portion of the pile above the water is not accessible to the beavers once the pond freezes.) According to beaver biologist Leonard Lee Rue, a beaver colony needs to store between 1,500 and 2,500 pounds of edible bark, twigs and leaves (this weight doesn’t include the wood, as they don’t eat wood) if it is to sustain them through the winter. As one would suspect, southern beavers do not need nor make winter food supply piles.

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Beavers Reinforcing Dams

10-15-13 beaver dam 208(Part 2 of 3 Beaver posts)
Beavers repair and strengthen their pond’s dam much as they do their lodge in the fall. New sticks are added and mud is retrieved from the pond bottom just below the dam, making the water deeper there than in the rest of the pond. Beavers dive down, dig up a load of mud and carry it beneath their chin and front feet to the dam. They then use their front feet to push the mud on top of and in between the pieces of brush on the dam (see front foot prints in mud, insert A). Because beavers spend so much time reinforcing their dam, it is not unusual to find their 1 1/2 –inch long, fibrous scat (insert B) in the water right below the dam (they keep their lodge relatively clean by defecating only in water).

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Beavers Refurbishing Lodge

10-14-13 refurbished beaver lodge 248This is the time of year when the industriousness of beavers can determine whether or not they survive through the winter. There are three major tasks for a beaver colony to tend to in the fall: refurbishing their lodge; strengthening and repairing their dam; and cutting and storing their winter food supply. They tend to perform these tasks in this sequence, tackling the lodge first. If the water level is high, the beavers will raise the floor of the lodge and the roof of the sleeping chamber. Every fall they add new material to the exterior of the lodge to strengthen the entire structure – typically sticks intertwined that create walls two feet thick or more. At this point the beavers coat the lodge with mud that they dredge up from around the base of the lodge (which greatly increases the depth of the water near the lodge). The apex of the lodge is not coated, allowing fresh air to filter down into the sleeping chamber. Once cold weather arrives, the mud hardens to the consistency of concrete, making the lodge is impenetrable to predators that can approach the lodge once the pond freezes. (In photo, note the fresh eastern hemlock branches and mud that have recently been added to the lodge.)

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Beaver Ponds & Waterfowl

6-5-13 mallard & ducklings 151The relationship between beavers and waterfowl is a strong one. In creating ponds and wetlands, beavers provide valuable waterfowl habitat. Beaver ponds are attractive to most dabbling duck species, particularly American Black Ducks and Mallards (pictured). Dead snags that are often found in beaver ponds provide Hooded Mergansers, Common Goldeneyes, Buffleheads and Wood Ducks with nesting cavities. During spring and fall, beaver ponds are used by migrating waterfowl, such as Green-winged Teal and Ring-necked Ducks, for the fuel they provide (aquatic invertebrates, plant seeds, tubers, buds and rhizomes). Waterfowl surveys in 2002 in Wyoming found that rivers and ponds with beavers had 75 times more ducks than those without beavers.


Beaver Scent Mounds

4-30-13 beaver scent moundsThis is the time of year when two-year-old beavers leave their lodges and strike out on their own, primarily because the woods surrounding a pond usually can’t support more than one family of beavers. Beavers are exceptionally territorial; once they’ve established a lodge, they do not take kindly to interlopers. In order to make this perfectly clear to house-hunting young beavers, in the spring resident beavers build what are called scent mounds — piles (up to three feet in height, but usually much smaller) of mud, leaves and pond-bottom debris — around the perimeter of their territory. They then smear castoreum, a substance that comes from their castor sacs, over the mound. Chemicals in the castoreum convey to roaming young beavers that this particular pond is spoken for.


Eastern Chipmunks Soon to Give Birth

4-24-13 dirty eastern chipmunk IMG_3051It’s possible that this chipmunk is preparing a nesting chamber in her underground burrow, judging from the amount of dirt that is on her. Sometime between February and early April chipmunks mate. Roughly a month later they give birth to 3 to 5 young in a bulky nest of leaves inside a 24” x 15” x 10” chamber. Within a week, hair and stripes will be evident on the young chipmunks. In about a month, they will venture out of the burrow, looking like small adults.


Goldenrod Ball Gall Fly Larva

3-22-13 goldenrod ball gall fly larva IMG_6182The round “ball” that is often present on the stem of goldenrod plants contains the overwintering larva of a fly (Eurosta solidaginis). A year ago an adult female fly laid an egg in the stem of the goldenrod plant. The egg hatched and the larva proceeded to eat the interior of the stem. As it did so, the larva excreted chemicals which caused the plant to grow abnormally, creating a ball-shaped “gall.” If you were to open a goldenrod ball gall today, you would probably find an overwintering larva (if a downy woodpecker or parasitic wasp hadn’t gotten there before you). Within the next few weeks the larva will pupate, and as early as April the adult fly will emerge from the gall, having crawled out the passageway that it chewed last fall. An inflatable “balloon” on its forehead allows the fly to burst through the remaining outermost layer of tissue at the end of the passageway. The adult fly lives about two weeks, just long enough to mate and begin the process all over again.


Coyotes and Beavers

3-12-13 coyote & beaver lodge2 IMG_6223A study of coyote prey (through stomach contents) in the Adirondack Mountains of New York revealed that beavers were second only to white-tailed deer. This photograph shows that, possibly for the last time this winter, a coyote recently took advantage of a still-frozen-but-fast-thawing pond by walking across it in an attempt to reach an active beaver lodge. Once there the coyote attempted to dig into it in order to reach the inhabitants. A hard, two-to three-foot-thick wall of frozen mud, logs and sticks kept the beavers well protected, as it was designed to.


Hibernating Queen Wasps

2-7-13 hibernating wasp queen2 IMG_2680The queen is the only wasp in a colony to live through the winter (the others all die), and she usually does so in a sheltered spot such as a rotting log or under the loose bark of a tree (pictured). I wasn’t aware, until discovering this wasp, that queens actually chew a cavity in which to hibernate, but that appears to be the case in some instances. You can see the woody bits of fiber under the wasp that accumulated from her excavating the chamber. The cavity is roughly one inch long and ¼-inch deep. As a rule, hibernating queen wasps protect their wings and antennae by tucking them under their bodies. Some species produce glycerol, which acts as an antifreeze, while others allow ice to form around their cell walls and simply freeze solid. Most queen wasps die over the winter, primarily from predation by other insects and spiders, not the cold. (The pictured wasp had succumbed.) Warm winters are more likely to affect queens, as they emerge from hibernation too soon and starve due to lack of food.


Renovated Bird Nests

Most songbirds only use their nest once. After their young have fledged, the nest is usually abandoned. In the natural world, recycling has been a way of life for a long time, and abandoned bird nests are not about to be wasted. In the spring, the material used in old nests is often re-used by birds building new nests. But long before this occurs, white-footed mice and deer mice, both of which remain active year round, often use old nests as larders where they store food for the winter. Occasionally they even renovate a nest in the fall in order to make a snug, winter home. They do this by constructing a roof (of milkweed fluff in this photograph) over the nest, which serves to insulate it. Use caution if you come upon such a nest– it could well be inhabited! (Thanks to Sara and Warren Demont for the photo op!)


A Great Christmas Present!

If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill.  A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!

One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”

In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e  book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”

I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!