Colony death by yellowjacket attack

Colony death by yellowjacket is common, but I’ve never heard as many yellowjacket stories as I have this year. People describe how colonies that seemed strong a month earlier are now gone, replaced by yellowjacket scavengers. Or they describe seeing yellowjackets freely entering the hive and seizing prey, undeterred by guards. What is going on?

What is a yellowjacket?

To be clear, a yellowjacket is a type of wasp that is usually black with yellow markings, although some may have white markings. In most places other than the United States, they are referred to simply as wasps. The species that cause problems for beekeepers are social insects that maintain large nests and raise their young on chewed invertebrates. Most species build a nest in an underground cavity, although certain species known as aerial yellowjackets build nests in trees or against buildings—nests that look very much like those of bald-faced hornets. In fact, aerial yellowjackets and bald-faced hornets are closely related, both in the genus Dolichovespula.

Why do they go after my bees?

Honey bees are particularly attractive to yellowjackets because one colony can provide a large supply of prey even late in the year. As an added bonus, the honey bee hive also contains larvae (food that doesn’t fight back), pollen, and honey. An entire smorgasbord awaits the predators who get through the door. Most yellowjackets do not forage very far from their home, usually no more than 1000 feet. So if you are seeing lots of yellowjackets around your hives, you have a nest fairly close by.

Wasps are beneficial insects

For the most part, wasps are considered beneficial insects because they eat many invertebrates that harm agricultural crops, including caterpillars. In fact, yellowjackets are scavengers and often do a good job of cleaning up the dead bees around a hive. The problem, of course, is they will keep coming back for more, especially as the weather becomes colder, drier, or other insects become scarce.

The yellowjacket life cycle

The life cycle of yellowjackets is very similar to that of bumble bees. Solitary mated queens overwinter in a protected spot. Early in spring, the queens emerge and begin looking for a place to build a nest. All by themselves they build a small nest, lay eggs, and provision their young with masticated insects. After the first set of workers emerge, those workers take over the job of raising the young and provisioning the nest, and the queen becomes a stay-at-home mom, spending her days laying more eggs.

Yellowjackets are worse in the fall

Honey bee populations peak in the spring and early summer along with the supply of pollen. As dry weather sets in and pollen becomes scarce, the number of honey bees in a colony decreases. So while the honey bee populations are decreasing, the yellowjacket populations are increasing, maxing out in August or September.

For that reason, yellowjackets in spring don’t seem like much of a problem—the ratio of ‘jackets to honey bees is insignificant and there are plenty of other insects for yellowjackets to eat. But by late summer the tables have turned and the earth is overrun by hungry wasps with a hankering for tender bees with yummy honey sauce.

The weather makes a difference

I can usually predict a bad yellowjacket year by the winter weather. A very cold winter with lots of snow, ice, wind, or rain will kill many of the overwintering queens. The probability of any individual queen surviving the winter goes down as the weather gets worse. Conversely, a mild winter will ensure a good crop of spring queens.

Then, too, if the summer is mild and wet, there will be plenty of insects around for the yellowjackets to eat. But if the summer is hot and dry, plants dry up, plant-eating insects die for lack of forage, and yellowjackets search for higher-risk food items, including honey bees.

This past year in western Washington, we were set up for a bad yellowjacket year due to a mild winter followed by a harsh summer. True to form, the wasps were out in force this fall—I’ve never seen more.

Weak colonies can’t repel an attack

A strong colony can usually hold its ground against yellowjackets, repelling them at the entrance. But colonies that are weak for any reason are vulnerable. Once you see a yellowjacket saunter freely through the hive entrance, you are in trouble.

Yellowjackets will sometimes bite off the the bees’ head, tear out the larvae, kill the queen, and break open honey cells. Once the honey begins dripping out of the hive, honey bee robbers will appear, and before long the colony is beyond hope. Sometimes the remainder of the colony will leave, more often they give up and become easy-to-catch prey.

Stopping a yellowjacket attack

Stopping a yellowjacket attack is difficult at best. You can close the hive, throw a wet blanket over the top, and wait. But usually, by the time an attack is evident, irreparable damage has been done.

I once watched an attack in action at a hive I had at an outyard. The property owner called to say that my bees were grouped under the hive stand. When I got there, the colony was indeed huddled below the stand and the hive itself was teeming with yellowjackets. I killed as many as I cold for an hour or more, but the supply never lessened. They’d torn open the honey cells and the brood cells, excavated the pollen, and were carting away bee parts as fast as they could.

Lessening the number of yellowjacket colonies

I learned a lot from watching that attack, and I have been proactive with wasps since then—perhaps overly so, but it is working for me.

I start in early spring with a reusable yellowjacket trap and a butterfly net. The important thing is to catch the queens early in the year. In the beginning the queens are out and about, doing all the initial work themselves. If you can kill them at this stage, you can prevent the establishment of a colony.

The pheromone lures get some, but I get more with the net. The queens are big, noisy, and easy to net. They need to eat frequently in order to do all that work, so you will see them drinking nectar at whatever is in bloom. Remember, yellowjackets don’t travel far from home, so if you can get a few queens in spring, you will save yourself a world of woe by autumn.

After the queens settle in, I have often found early workers by the sound they make as they scrape wood fibers for nest building. I have a woodshed made of unfinished lumber, and one time while I was out getting wood I was drawn to a distinctive scritching sound. On the outside of the shed were no less than five yellowjackets scraping the fibers off the siding. Last year, in the garden I heard the same sound and found two yellowjackets scraping wood fibers from unfinished tomato ladders.

The point is, killing the earlier individuals has the most impact on colony survival. The queen, of course, is the most important. But her first batch of brood is not large, so if you can get a good percentage of those, you may forestall the colony.

By late summer and early fall, killing an individual worker doesn’t make much difference. By then, you need to focus on protecting your honey bee colonies.

Preventing a yellowjacket attack

During early spring and summer, damage to honey bee colonies by yellowjackets is minimal. Bee colonies are large, yellowjacket colonies are small, there is plenty of food, and lots of water.

During this lush period you can afford fully open main entrances, upper entrances, ventilation shims, or any number of other openings. But once a nectar dearth begins, you have to reconsider how many openings your colony can defend. A large boisterous colony will be fine, but smaller or weaker colonies will probably need to be closed down.

Here in yellowjacket country, I reduce entrances to all but my largest colonies. The medium-sized ones I reduce to 4-inch by 3/8-inch main entrance, and the small ones to 1-inch by 3/8-inch. I remove all upper entrances and shims, and replace these with screened inner covers for ventilation. Since all my colonies have screened bottom boards, I am able to maintain through-the-hive airflow.

Even though both the yellowjackets and bald-faced hornets were cruising around the hives and cleaning up dead bees, none of my hives were breached this year in spite of multiple nests in the area.

During the fall, I also keep the pheromone lures fresh. Although they don’t seem to catch as many yellowjackets as I would like, they do catch some, so I keep going with it. All the homemade traps I have made have been a miserable failure, even though I’ve tried smoked turkey, ham, tuna, cat food, apple cider vinegar and everything else I’ve read about. I’m going to give up on that and stick with the commercial variety which use heptyl butyrate as an attractant.

Gone with the freeze

In temperate areas, the workers will all be killed with the first hard freeze, with only the queens surviving the winter months. In those places we get a reprieve from their antics and a little time to think about what to do next year. However, in the warmer areas of the country, nests may survive from year to year.

I feel for all the beekeepers who described their yellowjacket experiences to me, and I hope this summary will provide you with some ideas for next year. Who knew becoming a beekeeper meant learning so much about so many different things?

Rusty
Honey Bee Suite

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