Falling Leaves Reveal Mark of the Wasp

Now that the leaves have fallen from the trees, anyone who has gone for a walk on these crisps autumn days no doubt has seen a large gray object hanging in the trees. It is usually larger than a football and similarly shaped. So what are these things? They are the nests of the bald-faced hornet (Dolichovespula maculata).

Bald-faced hornets are a large, North American, stinging insect in the yellowjacket genus. It is actually not a hornet at all, but rather a type of wasp. The adults are about .75 to 1 inch long. It is easily identified by its white face, which gives rise to the common name. It also has three white stripes on the end of its abdomen. Other than that it is all black.

Each spring the female, also known as the queen, starts a new colony. She was born and mated the previous fall. She chooses a location for the nest, usually at the tip of a sturdy branch, and begins constructing the nest. As she does, she lays eggs inside the small nest and feeds the first group of larva. These will grow and become her workers, which are infertile females that only maintain the nest and care for the young. The more workers, the faster the nest expands, allowing the queen to lay more eggs and produce more workers.

The workers go out and forage for small amounts of wood that they chew up. Mixing the chewed wood with their own saliva, they make a wet papery paste that they spread around with their jaws. They form and shape the wet paste with their legs, and when it dries it forms the papery structure. This continues all summer, slowly building layer after layer until full size at the end of summer.

Each layer inside the nest consists of many egg chambers. The queen deposits an egg in each chamber. The eggs hatch and a grub-like larva emerges. After pupating (resting) for several days, the larva changes into the adult wasp. The job of some of the workers is to tend to the young exclusively. The job of others is to guard the nest, while others gather food. They eat tree sap, along with fruit, particularly apples. They also hunt down other insects, chewing them up and feeding them to the developing larva back in the nest.

Near the end of summer the queen lays special eggs that produce male drones and new queens. These males and females fly off together to mate. The females will be the only ones to survive the winter. The males will die with the first frosts.

As winter approaches the hives are abandoned and all the workers die. One or two cold nights below freezing and all the occupants will perish. The newly fertilized females will over-winter underground, under a log, inside a dead tree or other protected places. In the spring they will emerge and start the process all over again.

So if you are seeing one of these large nests in a tree at this time of year, most likely it is empty and will not be used next year. Raccoons, skunks and even squirrels will tear into these nests to eat any remaining larva. Until next time...

Source: http://www.chaskaherald.com