Focus on Stinging Insects: Born to Gnaw

It’s the pest management equivalent of a 911 call. "You’ve got to come over NOW," cries the panicked voice in the phone. "My house is filling up with BEES!"

Most seasoned veterans in our craft have received such calls, and will immediately recognize the scenario. Unless you live in the Southwest, the "bees" are more likely to be a colony of yellowjackets that have been discreetly nesting in a wall or ceiling void since spring. Now, several months later, they’ve outgrown their living space, broken on through to the other side, and cheerfully introduced themselves to your client — toothpaste style (which is to say, once they’re out of the tube and cruising through the house there’s no way of putting them back).

How could this situation have been prevented? It turns out that the biology of these formidable creatures is straightforward compared to selecting the most effective chemical tool to even the odds.

YOUR OPPONENT. Yellowjackets are small but feisty social wasps that are abundant throughout the northern hemisphere. Nineteen species live in the United States. A few of these (often called "hornets") typically build their familiar paper-maché nests in exposed locations, such as in vegetation or attached to the outside of man-made structures. But at least a dozen species prefer to nest in more protected sites. In prehistoric times, they were limited mostly to underground cavities. Nowadays, they also have the option of selecting concealed voids of buildings.

The size of a yellowjacket nest and the number of wasps living inside it vary widely within the group. Most nests are pretty small, ranging in size from a softball to a cantaloupe, and contain several hundred wasps at most. They rarely become pests, even when located in building voids, and tend to die out by early fall. On the other hand, six common species typically have much larger colonies, sometimes consisting of more than 5,000 individuals. These are the scavenging yellowjackets (occasionally called "meat bees" by the locals, although both carbohydrates and protein are fair game) that cause so much misery to people outdoors in late summer and autumn. Some of these nests may stay active into December, and in very warm climates, may even continue growing for a second year.

YOUR OPPONENT’S JAWS. So what’s the problem when they occur in structural voids? All yellowjacket nests are started in the spring by a single queen that mated the previous fall and survived the winter in a dormant state. For the most part, queens of cavity-nesting species are genetically programmed to search for inconspicuous holes in the ground that lead to old rodent burrows or other small, subterranean hollows. After a site has been selected, the queen constructs a little paper sphere, about the size of a golfball, in which she rears her first brood of workers. There’s usually not much room between this so-called "embryo nest" and the walls of its underground chamber.

When the first adult workers emerge, they take over all the foraging, construction, and brood care responsibilities. Part of their duties is to enlarge their cramped cavity to allow for the nest’s expansion. For a subterranean colony this generally entails scraping away the surrounding earth with their extraordinarily tough mandibles, and carrying it out when they leave to forage. Yellowjackets — totally unlike honey bees — are born to gnaw.

No one knows why some spring queens spend their time searching the walls of buildings for access holes to potential nest sites rather than concentrating on the ground, but those ingrained worker urges remain unchanged.

Figure 1 on page 50 shows what happens when nest meets suspended ceiling. If they can breach plywood just because they have all that nervous energy, you know they can burn through drywall or ceiling tile like it was butter if they seriously run out of room to grow.

Most buildings have dozens or even hundreds of potential entry points for yellowjacket queens, so for the most part, realistically preventing the "figure 1 syndrome" means catching the problem early. Careful exterior inspection to check for worker flight lines is critical. In addition, as a colony grows, more and more workers will simply wander away from the nest, lose their way, and emerge into the house through random openings. Knowing that these stray wasps represent "leakage" from a nest somewhere within the walls puts you and your client one step ahead of a potential crisis.

Figure 2 on page 54 shows a mature eastern yellowjacket nest (Vespula maculifrons) that had been built inside a wooden observation box set into a window. Just like inside most wall voids, space was not limiting, so there seemed to be no real need for the workers to gnaw. Nevertheless, every time I’ve studied a nest in this fashion, the compulsive little warriors still busy themselves by picking one or more weak spots (such as at joints) and scraping away that wood. A colony is fully capable of penetrating ¾-inch exterior grade plywood within a few weeks.

YOUR GEAR. Four pieces of equipment immediately come to mind:

Protective Clothing. It should go without saying that anybody who works with these creatures without wearing some sort of armor is begging to be hurt. This goes double if you’re up on a ladder. At the very minimum, use a bee veil, because your face is where you’re most likely to get stung. A full bee suit is much better, and never fails to impress the client. They’re available in old-fashioned heavyweight cotton or newfangled lightweight nylon or Tyvek.®

Ladder. A basic industry tool, so you’d think everyone would know how to use one. Proper ladder technique is usually covered in what should be mandatory safety courses for technicians. For those who prefer to remain earthbound, several extension products are available that permit chemical application to sites overhead. Some precision is lost with these tools, however.

Stethoscope. The actual nest site is usually fairly close to the workers’ access hole into the wall, but not always. In some cases, it can be completely remote. Although sound-amplifying devices are often recommended to pinpoint the exact colony location from inside the house, I strongly believe the most efficient way to deal with yellowjackets is through that exterior hole. Unlike honey bees, whose nests generally need to be removed to prevent the leaking of honey, the slight downside to a vacant yellowjacket nest (guaranteed dermestid production) usually does not justify the expense and disruption of opening up a wall to remove it.

Vacuum. The use of a vacuum to collect yellowjacket workers was pioneered by the late Roger Akre. He used it as a research tool, but it is now often suggested as a means for "least-toxic" colony control. As one of Dr. Akre’s students, I’ve vacuumed hundreds of nests over a period of 30 years, and can’t recommend it as a routine industry tool for this purpose. It is too time-consuming, control is typically incomplete and it requires a deceptive amount of specialized skill. On the other hand, vacuuming does have a number of advantages for void nests, and some clients are willing to pay a premium price for it. I’ll be discussing this technique in depth in a future PCT article.

YOUR CHEMICAL. Considering the substantial health threat posed by a yellowjacket colony in close proximity to indoor living space, I see nothing wrong with using a small amount of insecticide to safely eliminate them — provided the right product is selected and the right application technique used. There are two major issues to consider here. First, at all costs, you don’t want to excite or disorient the colony so that hordes of workers are driven more deeply into the structure and desperately emerge somewhere indoors. For example, in many houses it’s just a straight shot down from the wall void into the basement. Second, particularly with a large, active colony, you need to remember that there will be many workers that are still in the pupal stage. As long as they’re protected inside their dense silken cocoons (the "capped" cells of the brood combs), these individuals will be unaffected by any pesticide you apply.

Well, that begins to narrow the field somewhat. Remember resmethrin? It was marketed heavily a few years back for, among other things, void treatments for yellowjackets. It may have dispersed well in aerosol form, but like other synthetic pyrethroids, resmethrin acted basically as — how can I put this? — a flushing agent. I’ve had some colorful disasters with this product, although in fairness, others have used it without incident.

So the ideal weapon for our purposes would be a compound that is extremely toxic to yellowjackets, but also non-repellent. And the best formulation would be a dust, which could simply be puffed into the access hole from the outside and instantly coat its internal surfaces. As long as it’s applied quickly (so the wasps don’t get riled) and in minimal amounts (so it doesn’t plug the hole) all the workers will get a lethal dose while going about their normal business. In this regard, daytime treatment is more efficient than after dark, since it’s the in and out activity of the colony members through the access hole that brings most of them into contact with the pesticide. Best of all, the dust remains lying in wait to nail all those new workers emerging from their pupal cells.

Do we know of such a product? Of course. It was called Ficam D (bendiocarb), and for two decades it was the industry’s gold standard for dealing with cavity nests. However, unless you’ve been living on the back side of the moon, you also know that sales of this product ceased on Oct. 31, 2000. Quite a few companies purchased boxcars of the stuff before that happened, and still have enough in stock to get them through the current season. But, sooner or later, everyone will have to find an acceptable alternative. Drione seems to be the product most often mentioned, despite the risk of its pyrethrin content unacceptably irritating the wasps.

In my opinion, there has long been an even better choice than Ficam for killing yellowjacket nests in cavities. It’s called 5 percent Sevin (carbaryl) dust, its label bears the coveted "caution" designation, and it’s so toxic to Hymenoptera that less than 0.2 micrograms will kill a honey bee. Sevin is one of the three most commonly used insecticides in the United States and has been around since 1958, but its traditional customer base has been primarily the agricultural and gardening communities. Nevertheless, it is widely recommended for nuisance yellowjacket colonies by university entomologists and extension services.

There’s only one little problem with applying most Sevin dust products into building voids to control yellowjackets. The site is not on the label. Neither is the pest. It turns out you’ll find more than a few extension Web sites serving up erroneous information.

But the story does have a happy ending for industry professionals in many, but not all, states. There happens to be one, relatively little-known Sevin dust product that is indeed explicitly labeled for building cavities (and is indeed specified in at least two extension Web sites that I’m aware of). I’m hoping it becomes a lot better known soon. The formulation is called Apicide, and it’s manufactured by Mystic Chemical Products, Cleveland, Ohio. According to owner John Gedeon Jr., Apicide is sold mainly in the Midwest, although it has registrations in several eastern states as well. It’s marketed to the trade in 1-gallon pails that contain seven pounds of dust. That’s enough for a boatload of void nests, considering that one puff is usually sufficient for complete control. I’ve used this product for many years and have never failed to be impressed with its efficacy. If you can legally use it in your state, I recommend you give it a try.