Signs of Summer 8: Bald Faced Hornets!

Photo by Carney Lentz (Flickr)

I wanted to start this posting with a description of a nearby bald faced hornet’s nest. So, I walked around in the woodlots bordering my fields, and walked up and down the campus Nature Trail and was very surprised not to find at least one of these iconic, gray, football shaped nests. By now the nests should be nearly two feet long and a foot and a half wide and be a nexus of hornet activity. Maybe our cold winter was too much for the hibernating Queen hornets? Or, maybe the wet spring and summer were too hard on the developing nests? I really miss the hornets, though!

Many people are quite nervous around these insects (and with good reason!). Bald faced hornets can deliver repeated stings loaded with powerful toxins and tend to swarm any intruder that they perceive to be a threat to their nest and colony. But, their role in nature is not to harass or sting human beings! Let’s consider the good that these insets do in both their natural ecosystems and also in human dominated ecosystems. Having a large, robust colony of these hornets nearby (but too close!) is something all of us would benefit from.

Photo by Piccolo Namek (Wikimedia Commons)

The bald-faced hornet (Dolichovespula maculata) is a large (just under an inch long), black and white colored, social wasp that is found throughout North America. It is not a true “hornet” because that term is specifically used to describe wasp species in the genus Vespa. It is, instead, a member of the “yellowjacket” group (in spite of its very un-yellowjacket-like coloration!). The bald-faced hornet has many other common names including the “white-faced hornet,” the “white-tailed hornet,” the “bald-faced yellowjacket,” the “blackjacket,” and the “bull wasp.”

Their nest is made up of woody materials that have been chewed up by the Worker hornets and pulped into a mash with their saliva. This mash is spread out to dry in layers to form the walls of the growing globe. The nest contains multiple tiers of hexagonal combs all encased in about two inches of protective paper. There are air vents in the upper portion of the nest that allow the venting of excess heat. The nest begins as a very small structure but grows through the summer as the colony gets larger and larger. All of the Workers in the nest are the sterile, female offspring of the original Queen that started the nest in the Spring. These Workers have taken over almost all of the functions of the colony leaving the Queen with the exclusive job of laying more and more eggs. The Queen’s final task of the season will be to lay eggs for fertile females (new Queens) and fertile males who will then leave the colony, mate, and establish the overwintering, fertilized Queens for next year’s cycle.

Workers are very active outside the nest during the daylight hours of the summer. At night, they are active inside the nest caring for the larvae and pupae, and repairing and expanding the structure of the nest. During the day there is a constant flow of Workers in and out of the nest. These Workers are bringing food into the nest (flower nectar, fruit pulp, tree sap, and a great variety of insects upon which they prey. Larvae are fed a rich mash of crushed up insects gathered by and fed to them by the Workers.

In the process of seeking out flower nectar, the bald-faced hornets may be contributing to the spread of pollen from flower to flower and thus may act as an agent in the reproductive cycle of many plants. The fact, though, that these wasps have very smooth bodies (as described by the “hairless” or “bald” adjectives in a number of their common names) means that very little pollen actually sticks to them. They are thought to be a much less effective pollinator species than say the much hairy honeybee or bumblebee.

The impact of these bald-faced hornets on other insect populations, though, may have great ecological and even human significances. They prey avidly on a wide range of insects but seem to be especially fond of various species of dipterans (“flies”). Deer flies and horseflies are an optimal prey size, and I have observed swarms of bald-faced hornets taking these biting dipterans in very large numbers.

Many years ago Deborah and I had a horse named Ahab. Ahab, like most horses, was really bothered by deer and horse flies in the summer. Ahab learned, though, that he could stand, motionless with his legs spread next to a line of black walnut trees (one of which had a bald faced hornet’s nest in it), and the hornets would sweep across his legs and back grabbing up the biting flies. The hornets would then fly to the rails of nearby fence and rip the flies apart in a feeding frenzy. I even watched some of the hornets hovering behind Ahab’s legs waiting in ambush for a deer fly or horse fly to blunder by. This was like a cleaning station in a coral reef in which small fish swarm over larger fish to pull off and consume their parasites! Ahab always had a bit of nervous expression on his face, though, when he was standing at attention in the hornet swarm!

So, bald faced hornets eat deer and horse flies! NO ONE likes deer or horse flies!! The enemy of our enemy, then, is our friend! If anyone sees a bald faced hornet nest, please let me know! I hope that there are enough of them out there to keep the deer flies and horse flies in check!