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OCT. 16, 2018

Yellowjackets, it’s a zen thing.

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Aahh, autumn, and our thoughts here in the Blue Ridge turn to cool, clear days and ground-nesting yellowjackets. We have two “hornets” here in the mountains – the big, bald-faced “hornet” (Dolichovespula maculata) that makes the basketball-sized paper nest we see hanging in trees, and the small (5/8″) Eastern yellowjacket (Vespula maculifrons) that constructs a similar paper nest, but underground. Taxonomists classify them both as yellowjackets. All wasps, ants, and bees are in the Order Hymenoptera (membrane-winged) and the social wasps (as opposed to the solitary wasps) are in the family Vespidae. Most of these make paper nests. Our small yellowjackets make theirs underground.

Most of the social wasps, ants, and bees have caste systems with a fertile queen (and, when needed, fertile males) and sterile female workers. Nearly every wasp, bee, or ant you see is one of these sisters. A single queen starts a new colony in the spring after overwintering in a hollow tree or under a log. She has stored sperm from her mating the previous fall and constructs the first few cells of the nest, lays eggs in them and feeds the larvae, which pupate and emerge as the first workers. After that the queen remains in the nest, lays eggs and is tended by her daughters. These workers enlarge the nest all season, adding lower “stories” of cells and covering them with the protective outer paper nest. Occasionally you might see wasps scraping logs or fence posts to gather the fibers, which are then mixed with saliva to create this paper. The workers forage for food – nectar for themselves and insect prey for the larvae, which they first chew for them.

Late in the season the workers will build a few large cells and feed the larvae in them special high protein meals; these will become new queens. At the same time, the queen will lay some eggs from which she has withheld sperm – unfertilized eggs – which will become males, called drones. New queens and drones leave the nest to fly high into the sky for mating after which the drones soon die and the queens look for sheltered sites to spend the winter. The old queen is probably dead by that time and the colony breaks down. The workers fend for themselves, sometimes eating the remaining larvae (their baby sisters!) until they die with the approach of cool weather. So, although you could find a straggler or two inside, the nest is abandoned at the end of the season and you are doing no harm in collecting it, although I have read that it may be used as a winter retreat by mice. At any rate, it will not be reused by yellowjackets in the spring.

As you may know from experience, the sting of a yellowjacket really packs a punch. Justin Schmidt, who developed a four-point pain scale for insect stings, gives the pain from both our yellowjackets a solid two.  For Dolichovespula he records: “Rich, hearty, slightly crunchy. Similar to getting your hand mashed in a revolving door” and for a Vespula sting: “Hot and smoky, almost irreverent. Imagine W.C. Fields extinguishing a cigar on your tongue.” More importantly than the pain, for some folks a sting means anaphylactic shock, which may become life-threatening, requiring treatment and hospitalization, so anyone stung should be watched for signs of an allergic reaction.

These social wasps are considered to be more highly evolved than the solitary wasps, which use their stingers (which are modified ovipositors which means only female wasps sting) to paralyze prey. The defensive stinging of yellowjackets delivers a complex of familiar hormones – acetylcholine, serotonin, and histamine. Variations of this toxin are also seen in scorpions, jellyfish, and even nettles. Acetylcholine is a neurotransmitter of the parasympathetic system, which is involved in involuntary responses. Serotonin induces vasoconstriction. Histamine is released in response to tissue damage and invasion by foreign substances and causes your blood vessels and capillaries to dilate and begin to leak plasma and it also triggers inflammation. No surprise that yellowjackets display aposematic or warning coloration to discourage predators.  Black bears, raccoons and skunks may be their only mammalian predators here since they sometimes brave the stings to tear open a nest to get at the juicy larvae.

So, why are these girls so fierce? Actually, when they are foraging they are quite docile, as you may have noticed as they steal meat from your sandwich. But when you threaten the nest site, they go ballistic, stinging repeatedly and pursuing you down the trail Yogi Bear-style. This is a classic example of kin selection theory from sociobiology. The workers are non-reproductive but they share the queen’s DNA, so protecting the colony equals protecting the queen equals protecting their investment – their only reproductive option. The more genetic information you share with another, the higher your interest in keeping them alive should be.

It really, really is true that even yellowjackets are fairly docile if you leave them alone. They pretty much only sting in defense of the hive site, so don’t swat at them or freak out if they are just trying to share your sandwich. Take the opportunity to observe them closely and calmly. It’s a zen thing.

By Ted Wesemann, Natural Science Teacher