Beavers Preparing For Winter

The lazy, hazy days of summer are dwindling, and beavers’ internal clocks are telling them it’s time to batten down the hatches and prepare for several months of life below the ice. This entails adding a significant amount of mud to the outside of their lodge. The mud freezes and creates an impenetrable barrier between them and predators such as coyotes that, thanks to ponds being frozen, will have access to beaver lodges. This mud is anchored by the addition of debarked branches and logs that have provided the beavers with meals of cambium during the summer.

A beaver can transport its own weight in material (roughly 45-60 pounds). Retrieving debarked pieces of wood in many cases involves carrying them over both land and water, using only jaws and sometimes a shoulder for support.  A beaver’s short, muscular neck and its powerful lower jaw muscles make this possible. Try lifting one of the larger logs on a lodge or beaver dam sometime. Then imagine carrying it any distance in your mouth with no assistance from your hands. (This feat rivals that of a moose carrying two 25 – 30 pound antlers around for several months.) While there are recorded cases of beavers felling trees 150 feet tall and 5 feet in diameter, logs of this size are not used as building material for dams and lodges, but rather the bark and upper branches provide them with food.  (Thanks to Roger and Eleanor Shepard and Sara and Warren Demont for photo op.)

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Geometrid Larvae Dangling

The larvae of moths in the family Geometridae (the second largest family of moths in North America) are known as loopers, inchworms and spanworms. These names are derived from the looping gait of the caterpillars. They generally have only two or three pairs of prolegs (at the hind end) rather than the usual five pairs of most moth and butterfly larvae. The lack of prolegs in the middle of their body causes them to move by pulling the hind prolegs up to the true legs on the thorax in the front of their body, thereby forming a loop, and then extending the body forward.

Many Geometrid caterpillars evade predators by flinging themselves from trees and dangling by a silk thread that is attached to the tree at the other end (see photo). After the danger passes, they climb back up the silk and return to their leaf-eating.

Blue Mud Dauber Wasps Building Nests

Yesterday’s Mystery Photo showed evidence of a Blue Mud Dauber Wasp (Chalybion californicum) scraping the mud with its mandibles as well as the resulting ball of mud it had formed to use as building material for its nest.  You can get a hint in this photograph of the iridescent blue wings that give this wasp its common name.

Mud dauber is a common name for solitary wasps that make individual nests for their eggs/brood with mud. There are many species of mud daubers, but most are between one and one-and-a-half inches long, black or metallic blue, and typically have a narrowing, or “thread-waist,” between their thorax and abdomen.

Most species of mud daubers, after making a small (1/4” diameter) tube nest out of mud or refurbishing an old nest, leave to forage for spiders. Once a spider has been located, the wasp stings and paralyzes it, but does not kill it (so as to prolong decomposition), carries it back to its nest, and repeats this process over and over until the nest is stuffed with living prey. The wasp then lays an egg in this mass of spiders and seals the nest with mud. The egg hatches and the wasp larva consumes the spiders as it grows. After pupating in the fall, the adult wasp emerges in the spring, mates and the cycle continues.

The reason that the ball of mud that the Blue Mud Dauber had formed was not taken back to the nest site as building material appears to be a small rootlet which anchors the ball to the ground, preventing the wasp from removing it.

Mystery Photo

Look closely at this photo and you will see markings in the mud as well as an abandoned spherical, muddy structure about the size of a pea. Who has been here and what have they been doing? (Enter your answer under “Comments” on today’s post at http://www.naturallycuriouswithmaryholland.wordpress.com.)

Black Bears Foraging

This is the time of year when Black Bears are looking for every available source of food in order to bulk up before entering hibernation. During this period of gorging (hyperphagia) Black Bears consume large quantities of fruits, berries, nuts, grasses, roots and insects.

In particular, they favor the brood (larvae and pupae) of ants, due to their relatively high content of fat and protein. Black Bears find brood by detecting the pheromones and other chemicals such as formic acid that ants use for communication and defense. Research has confirmed that Black Bears will dig up as many as 200 ant colonies a day, flipping rocks, moss and leaf litter over and tearing apart logs, stumps and snags (such as the one pictured), using their canine teeth and claws to gain access to the ants. Once they have torn apart the stump or snag, they use their long, sticky tongues to gather brood. Anthills are avoided except for when Black Bears are extremely hungry, due to the fact that bears prefer not to get a lot of soil or sand mixed in with the brood they’re eating. (Thanks to Virginia Barlow for photo op.)

Shadow Darners Laying Eggs

The dragonfly family Aeshnidae consists of strong-flying dragonflies called darners, some of which are over three inches in length.  The majority of darners reach the peak of their population in August and early September.  Male Shadow Darners (Aeshna umbrosa) can be seen patrolling breeding sites a few feet over the water’s surface, searching for females and driving off competing males. Females can be observed repeatedly landing at the base of cattails, inserting their sharp-edged ovipositors and slicing open leaves, where they then deposit their eggs.  If you look at the bottom third of cattails at this time of year, near the water’s surface, you will find tiny, tan, vertical slits where dragonfly egg-laying has taken place. (Photo:  female Shadow Darner laying eggs)

Grasshoppers Molting

Molting is the process by which insects and other arthropods grow. They have an external skeleton (exoskeleton) that supports and protects their body, unlike the internal skeleton of most other animals. Since the exoskeleton is hard and its outer layer is non-living, it cannot grow bigger by small increments as the human skeleton does. As an insect increases in size, it sheds the inelastic exoskeleton on the outside of its body, and replaces it with a larger, soft exoskeleton that has formed underneath the smaller, shed exoskeleton. Eventually this new exoskeleton hardens. This process is repeated several times during the life span of an insect (the exact number depends on the species).

Grasshoppers experience incomplete metamorphosis: they go through three stages in their life cycle – egg, nymph and adult. Nymphs are miniature versions of adult grasshoppers, except that they are usually light in color and do not possess functioning wings. Nymphs undergo five or six molts and with each molt their size increases and their wing pads progressively develop. Usually within a month nymphs molt for a final time, emerging as adults with fully developed wings. (Photo: shed grasshopper nymphal skin showing small, developing wing pads; inset – fully mature grasshopper)