Earwigs Gone Wild!

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In 2006, a retired couple built a log cabin at the top of a mountain for a vacation home.  Abeautiful home in Bostic, NC with gorgeous views of the Blue Ridge Mountains, the type of place I aspire to have one day. One late spring day, soon after the home was built, they were sitting on their deck enjoying the view when they noticed a swarm of insects arising from the surrounding tree tops.  They watched this swirling mass of insects as it moved overhead.  Then, they started hearing the “ticks” as the insects fell from the sky and landed on the metal roof of their home.   It sounded like rain as the number of falling insects increased, landing on the roof, the deck, and on them.  They recognized the insects were earwigs and they quickly went inside.  The days that followed turned their dream home into a nightmare.  Thousands of earwigs began working their way into the house, pouring in from every crack and crevice they could squeeze into.  They began falling from the
ceiling and walls from the natural cracks in the wood logs, and the hardwood floors were covered with earwigs running about.
As the summer months passed, more swarms of earwigs came from above and
inundated the house.  They clogged the gutters and downspouts; they worked their way into the toilets, cabinets, closets, and every drawer in the house, and fell onto the beds during the night.  The homeowners couldn’t go anywhere in the home without seeing earwigs, stepping on earwigs, or having earwigs crawl on them.  Every couple of days they would sweep and use a shop vac to suck up the earwigs, which had to be emptied regularly because the bucket of the vacuum would become full.  During this time, the technician and manager of the local branch visited several times to apply a variety of insecticides in and around the house.  These treatments would kill thousands of earwigs, but in the words of the branch manager, “thousands more would come to their funerals.”
Our technical director and an extension entomologist from NC State also visited the house but neither could offer an explanation as to why the earwigs were there.   Soon after, the weather turned cold and the earwigs finally died off over the winter.  The following spring, however, they came back with a vengeance.

When I heard about what was happening, I had to see if for myself.  Partially because I didn’t believe it, or at least I couldn’t believe that what they were seeing were actually earwigs.  I was so skeptical that it didn’t occur to me that everyone involved could correctly identify an earwig.  The reason for my skepticism was because what the earwigs were doing went against everything I knew about them.  First, I had never heard or read about
earwigs swarming like termites.  They have wings (the flight wings are folded underneath the short forewings which act as protected covers) but rarely, if ever, fly.  I have observed a few earwigs flying about porch lights at night, but never swarming en masse during the day.  This is another odd detail since earwigs are mostly active at night.  Earwigs also
prefer to be in moist, or humid, habitats such as under mulch, pine straw, leaf
litter, or in rotten logs.  There they feed on organic matter, small insects such as springtails, and sometimes plants.  The conditions inside the home were far from favorable for them.  It was not moist or humid, nor was there an abundance of food.

I arrived at the house just after a fresh swarm.  Even with what I had been told, I could not
believe what I was seeing.  It was reminiscent of a horror flick where the walls were crawling with creatures.  We began our tour by walking around the outside of the house.  I was silent in awe as I watched thousands of earwigs running up and down the outside
walls, crawling on the ground, and running up and down nearby trees.  Next to the foundation were piles of dead earwigs, heaped up like mounds of dirt, which accumulated as a result of the numerous insecticide applications.  I didn’t say much, other than “Wow, this is insane”.  The branch manager turned to me and said, “Let’s go inside, you haven’t seen anything yet”.  The homeowner greeted us at the front door and led us to the large open family room.  She explained that they had just returned the day before.  In the middle of the room was a ladder with a spent “bug bomb” sitting on it.  They had
set off several of these total-release insecticide canisters (without our approval of course) before heading to their main house a week ago.  She had already swept the floors in the
family room that morning, but there were still hundreds of earwigs running
around and falling out of the cracks in the walls.  She showed me a small kitchen trash can half full of earwigs to prove to me that she had indeed swept up earlier.  She then led us to the upstairs bedrooms where she had not had a chance to sweep and vacuum yet.  The floors in each bedroom were literally covered with them.  As we walked around
they would crunch under our shoes and the floors would become slick to walk on
from all of the crushed earwigs.    I said to her, “You are very tolerant and patient.  If this was my house, my wife would have burned it down by now”.  She explained that she probably is more tolerant than most people, but the whole ordeal has been extremely frustrating.  I told her that we would continue to do everything possible to get this under
control.  I really felt bad for them and I really wanted to figure out what was going on.

I visited the house a few more time over the next couple of years.  I always left with more
questions.  I sent some samples to Clemson University to confirm that they were indeed European earwigs (Forficula auricularia).  During my visits I tried to find where they
were breeding.  I knew they weren’t breeding inside the house, I never found eggs or nymphs.  There was some mulch around the house, but not an excessive amount.  I searched in several places under the mulch but never found earwigs living there.  Strange because this is one place you would expect to find them.  The house was surrounded by forested areas.  In these surrounding woods there were several old dead trees, some still standing.  When the bark was peeled from these standing dead trees, earwigs would pour out like a waterfall.  The standing dead trees were full of earwigs, but there were very few in and around the logs on the ground were you would expect to find them.  Only adults were found, no eggs or nymphs.  The further into the woods I went in search of earwigs, the less I could find.  It seemed as if the house was the central gathering points for the earwigs, the closer you got the more earwigs there were.  Even other houses in the
neighborhood did not have earwig problems.  After all my investigations, I could not find one breeding site.  During my visits I would also apply treatments recommended by industry reps and distributers.  I tried a variety of baits, but the earwigs would not touch them.  They were not eating and they weren’t breeding, so why were they there?

I did some research and reached out to fellow entomologists.  I talked with my advisors
from Clemson University, I contacted the professor of urban entomology at the
University of Florida, and I posted the situation on the Urban and Structural
Pest forum in the Entomological Society of America.  Nobody had ever heard of a situation like this before.   On pages 224 to 225 in The Handbook of Pest Control (Mallis, 8th edition), there is a little history on European earwigs that grabbed my attention:

“For a few decades following its North American introduction, population explosions of the European earwig were common.  Fulton (1924a) gives the
following graphic description:  “At night, they swarm over porches in such numbers that many people prefer to remain inside on a summer evening, rather than spend it with such unwelcome guests.  In the morning, earwigs are found by the handful under rugs and cushions which have been left outside.  They crawl into basements and hide in the
laundry which is waiting to be ironed.  In the bedrooms, they sometimes find their way into the clothing hanging in closets.  A man reported that he pulled on a sock one morning which contained three earwigs.  …They work mostly at night, but in the
daytime might be found in kitchen drawers and often burrow an inch into a load
of bread.  They crawl over the ceiling and drop on the bed, or inhabit themselves in a person’s clothing during the night.  And while their bite has never proved serious, it is entirely uncomfortable.  No part of the house seems to be entirely free from earwigs, not even the roof, and it is almost impossible to keep them out by the use of screens.”  In more recent times, populations of the earwig have stabilized in most of it geographical range and only occur in large populations when environmental conditions are favorable.”

This account was very similar to what our customer was experiencing, except the
swarms were happening during the day.  Perhaps the European earwig had just now arrived in that particular area and being newly introduced with no natural enemies caused them to create massive population explosions like what happened when first introduced into other areas of the U.S.  This species was accidentally brought into the United States around 1912.  The Eastern and Western U.S. recorded their presence at about the same time.  By the early 1920’s the earwigs were so bad in the Pacific Northwest that Colorado
formed the Bureau of Earwig Control.  They began control efforts by dumping 200 tons of “earwig bait” (I haven’t been able to find exactly what this was) over 30,000 lots.  This provided some relief but the earwigs came back the following year.  Entomologists then began importing parasitic Tachinid flies from France.  These flies are natural parasitoids of European earwigs.  They lay their eggs on or near the earwigs and the larvae feed and develop inside the earwig once they hatch.  A large facility was built with the specific purpose of raising earwigs and then parasitizing them with these flies. The parasitized
earwigs were distributed widely and were also sold for a penny a piece.  These flies (Triarthria setipennis [formerly Bigonicheta spinipennis]), are now widespread throughout the U.S.  The Bureau of Earwig Control was eliminated in 1929 in a swirl of controversy when it was discovered that they made thousands of dollars by requiring unnecessary baiting of earwigs and charging homeowners for it.

If the earwigs were so numerous around this house because they were new to the area, why weren’t other homes in the area being affected?  The swarms began shortly after the house was built.  Was there some kind of attractant in the logs or staining used in the
construction of the home?  It has been found that earwigs do have an aggregation pheromone (Walker, 1993) but the specific chemical components have not been isolated to my knowledge.  The logs were purchased from a popular log home dealership and the wood stain was a commonly used brand.  If there was some kind of earwig attractant (or
aggregation pheromone mimic) in the chemicals used to treat the logs or in the stain, wouldn’t there be more occurrences of earwig infestations in the homes that have used these products?  During one of my visits I used some pieces of spare logs saved from the construction of the home and stained some with the same material the house was stained with and placed these stained and unstained logs in areas away from the house to see
if earwigs were attracted to them.  So far, no earwigs have been found around these logs.

This past fall, the earwigs were lingering a little longer than usual.  They had been dying off rather quickly after the onset of cold weather in the past.  I decided to use a
micro-injector machine to do a thorough treatment on the inside.  This machine converts the insecticide into a fine mist and pushes it deep into cracks, crevices, and voids.  There are several cracks and crevices in a log home and I spent hours treating the inside on a day when the homeowners were not there.  A few days later when they returned, they called and said they had found many dead earwigs but none that were alive.  I felt good that my
treatment was effective and has provided relief from the remaining earwigs.  The next day they called and said there were now hundreds of earwigs swarming inside the house!  After a few more weeks of sweeping and vacuuming earwigs, they finally disappeared for the winter.  Now we had a few months to come up with another plan before the swarms start again in the spring.

It was an unusually wet winter.  It seemed to be raining every day for weeks on end.  Lake levels rose, rivers overflowed, and the mountains received record snow falls.  Because of this, I was extremely nervous that the earwigs would be even more numerous this year when the weather became warm.  We had to do something to prepare.  In mid spring a team of technicians and I went to treat the house to hopefully repel the earwigs when they start swarming.  In the past years the first swarms have been showing up around the end of May and beginning of June.  For a while, no swarms appeared.  The homeowners have found a couple dozen earwigs in the house so far, but no large swarms.  Had they finally settled down?  During the spring the homeowner commented on the large numbers of lady beetles, paper wasps, and flies that had apparently overwintered inside the home and have now found their way into the living areas.  These overwintering insects are quite common in the area.  The flies, I assumed, were cluster flies.  Thinking back, perhaps these were not cluster flies.  Perhaps they were the parasitic Tachinid flies that have now come into
the area, drawn in by the large numbers of earwigs.  I have read that they resemble house flies, but are larger.  This is the same description for cluster flies, so it might be easy to confuse the two.  Perhaps nature has corrected the situation, as what happens many times when there is an unbalance.  Perhaps the earwigs will return in large numbers.  Unfortunately, that is exactly what they did.  The swarms did arrive again that year, just later in the season than they had in the past.  A few months of vacuuming and treating with repellent insecticides passed and when the cooler weather in the fall hit, the
numbers again died down.

Thinking that the attractiveness of the house might have something to do with the wood stain that was used, I advised the homeowners to re-stain the house with a different
product.  Not only did they re-stain the house, they also worked feverishly to caulk and seal as many entryways as possible.  This was a daunting task for a log home.  The next spring arrived and we treated the house thoroughly with repellent insecticides in anticipation of the swarms.  Then we waited.  Amazingly, the swarms did not come.  In fact, over the summer only a handful of earwigs were seen.  Did we figure it out?  Was it indeed something to do with the wood stain that was originally used?

Later that summer a tornado came through the area and caused some damage to the house along with a few downed trees.  The homeowners took this opportunity to eliminate as many standing dead trees as possible from around the house in case they were being used as harborage by earwigs.

For a while, things looked great.  The earwigs seemed to have gone away.  But, the next summer I received a phone call and was told the words that I never wanted to hear, “The earwigs are back.”

So, we still have not figured it out but we continue to work on it.  This Spring we thoroughly treated the house with some new products before the “swarms” were anticipated.  Amazingly, they did not appear this year.  We all hope it stays that way.