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Bald-faced Hornet Nests

Bald-faced Hornet Queens Laying Specialized Eggs

A Bald-faced Hornet colony begins in the spring when a queen emerges from winter hibernation. The queen builds a small nest, creates a few brood cells within the nest, deposits eggs in them and feeds the larvae when they hatch.  These larvae are female workers — they will continue the nest building, food collection, feeding the larvae and protecting the nest while the queen concentrates on laying eggs.

During the summer the colony (and size of the nest) grows until there are between 100 to 400 workers. Toward the end of the summer the queen lays two special types of eggs. The first will be, like the workers’ eggs, fertilized eggs that will develop into females, but these females will be fertile (and develop into queens). The second group of eggs will be unfertilized eggs. These eggs will develop into fertile males. The maturation and emergence of the new queens and the fertile males marks the end of the functioning of the colony. At this point the workers are not replaced and die out. The ruling queen, having served her purpose, also dies. The newly-emerged adults (queens and fertilized males) leave the nest, mate, and the fertilized queens overwinter and begin their colony cycle all over again in the following spring.  Some small nests complete their cycle by mid-September, while some large nests are still going strong until the cold kills the larvae in late November.


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)

Black Bears Raiding Brood




Red-eyed Vireo Nests

1-28-16 red-eyed vireo nest IMG_6315

The Red-eyed Vireo’s nest is indisputably a work of art. Unlike most songbird nests, it is suspended below the branch to which it is attached. Perhaps the observant eye of Arthur C. Bent, a compiler of firsthand bird observations in the early to mid-1900’s, describes it best.

The red-eyed vireo builds a dainty little pensile nest suspended usually from a forking, horizontal branch of a tree, rather below the level of our eyes as we walk through second-growth. The nest is a beautifully finished piece of workmanship, constructed of fine grasses and rootlets, bits of birch bark, and paper from wasps’ nests, bound together and to the supporting branches with spider’s or caterpillar’s webbing, and , perhaps the most constant material, long, narrow, flexible strands of grapevine bark, which help to hold up the cup of the nest.

As mentioned, pieces of Bald-faced Hornet nests are frequently incorporated into the outside of a Red-eyed Vireo’s nest. These papery bits of hornet nest are purely decorative, and serve no structural purpose. Hornets are aggressive and defend their nests vigorously, so much so that it is unusual to find birds nesting in close proximity to a hornet nest. A vireo nest covered with papery bits of a hornet’s nest looks very much like a young hornet nest. It is conceivable that the use of this decorative material is a strategy employed by vireos to ward off potential nest predators.
