Midges and the Monument

If there is a single edifice that can be considered the most venerated national shrine for the United States, it would be the Lincoln Memorial in Washington, D.C. Constructed of luminous white marble in the form of a Greek Doric temple, the imposing monument was built on man-made terrain (“reclaimed swampland” in civil engineering terminology), now called West Potomac Park, that was created as a flood control measure by the Army Corps of Engineers in the late 1800s, using dredged material from the Potomac River’s original channel to build up its tidal flats.

At the time of the memorial’s construction in the early 1900s, the site was marshy and unpleasant — malaria was still endemic in the area — and thus considered by some to be a highly inappropriate location for the project. The structure is about 200 yards from the riverbank.

The memorial has been periodically vandalized with paint, eggs and scratched graffiti, requiring the services of experts to restore. However, it is the routine cleaning of the building and its massive statue that constitutes one of the greatest ongoing maintenance challenges for the National Park Service — indeed, the technologies involved in cleaning any historic structure remain the subject of a passionate debate among preservationists, considering the potential harm may outweigh any benefit.

As a relatively soft, porous stone that is extremely susceptible to etching by abrasive or even mildly acidic substances, marble is one of the most problematic of building materials to maintain over the years. Even the physical action of water used to wash it will gradually, grain by grain, erode away its surface.

And in addition to the usual grime that buildings normally accumulate, including airborne pollution from vehicles and the almost universal bane of bird droppings, the Lincoln Memorial must contend with another major source of esthetic and structural defacement due to the unanticipated karma of its once controversial location.

At least for the foreseeable future, the monument will be inextricably bound together with its midges and the spiders that feed on them, both contributing abundant deposits of their acidic excrement and creating, in the words of a 1990 commissioned report, “an enormous, unsightly visual nightmare.”

MISTAKEN IDENTITY. At one time, the National Park Service assumed that the black, greasy spots that festooned the outer walls and columns were mainly droplets of jet fuel residue from the air traffic flying overhead from nearby National Airport (which, in fact, are also present on the marble). They were certainly not linked with the annual buildup of grayish spider webbing over much of the structure, which as an account in the Washington Post noted, gave the memorial “a slightly moldy look.”

The response for decades was simply periodic reactive cleaning. Although scaffolding was erected twice a year to steam the interior chamber walls (which in the 1970s cost about $3,000 to $5,000 in labor), the exterior walls generally were blasted once a year with pressurized water.

The beginnings of the National Park Service’s recognition of its midge predicament are poorly documented, but apparently began with consultant work in 1974 by entomologist Ernest C. Bay, serving a brief stint in the Department of Entomology at the University of Maryland, who established that much of the dark residue was from the bodies, droppings and prematurely deposited egg masses of chironomids (gravid females of the area’s principal species, Chironomus plumosus and C. attenuatus, are particularly attracted to light), and since the insects swarmed mainly at twilight and shortly thereafter, simply waiting until one hour after sunset to turn on the memorial’s floodlights would greatly mitigate the situation.

SIMPLE SOLUTION. The advice was first implemented in 1981 through the efforts of National Park Service architect-historian Paul Goeldner, whose memo the following year established the modified schedule as normal procedure until 1988, when the automatic timing system malfunctioned and the midge/spider problem sharply intensified.

By coincidence, 1988 also marked the onset of a major initiative by the National Park Service to address a multitude of increasingly hard-to-ignore issues with structural degradation of both the Lincoln and Jefferson Memorials. Coordinated by the firm of Hartman-Cox Architects, a multidisciplinary team of consultants was commissioned to assess the buildings’ status and make recommendations for remediation. Cascading damages due to midges was a conspicuous target of the investigation, and the expert hired for this purpose was another University of Maryland faculty member, dipterist and ornithologist Donald Messersmith.

One might think the topic had already been adequately explored, but those who have never worked for a large organization with high levels of churn have no idea what a few years makes in eroding institutional memory (which is even more fragile than marble under the best of circumstances).

What might be considered as the second iteration of the National Park Service’s midge awareness is chronicled in three hefty reports on the Lincoln Memorial alone, two prepared by Hartman-Cox in 1990 and 1991, and a third devoted primarily to lighting assembled by the firm of Einhorn Yaffee Prescott in 1993. Together, they provide an instructive example of the enormous amount of expertise, care and study exerted behind the scenes by specialists dedicated to preserving the world’s cultural heritage.

More sobering is the documents’ in-depth accounts of how rapidly and comprehensively structures disintegrate. Within a span of only two generations, a sacred monument supposedly built to last for the ages had decayed to the point where its problems included (as Hartman-Cox put it) “the deterioration of the concrete slab at the entrance approachway, the deterioration of the marble and mortar, general moisture intrusion, and the severe infestation of insects and birds.” Regardless of the type of building, historic preservationists are thus in exactly the same boat as pest managers, dealing with inexorable entropy that ensures their job will never be done.

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Messersmith’s involvement with both midges and birds at the Lincoln and Jefferson Memorials took place over a period of several years, but it is his 1990 demonstration of applied midge biology that has become a classic in structural IPM lore.

For a six-week period from mid-April until the end of May, the onset of external lighting on the structures was delayed by one hour after sunset (i.e., turned on about 8:45-9:30 p.m.) on Mondays, Wednesdays and Fridays. The other days, they were turned on at their regular time of 6:00 p.m. With the assistance of two students, Messersmith monitored midge numbers in four one-meter sampling squares on both buildings.

The trial had two dramatic effects. The first concerned the tests results, which were strikingly positive. Although midge flight was noticeably suppressed due to unusually cold spring weather, 49 individuals at the Lincoln Memorial were counted on the delayed lighting nights compared to 510 on normal evenings (a 90 percent reduction); and at the Jefferson Memorial, 52 compared to 264 (an 80 percent reduction). “Professor Shines New Light on Monumental Midge Mystery” proclaimed the Washington Post.

The second effect was on public reaction to the brief blackout periods, which was strikingly negative. From a 21st century perspective, it may seem incongruous that the Lincoln Memorial was not originally equipped with electric lighting until one considers that its design began in 1897, construction initiated in 1914 and completion finally accomplished in 1922 (just as incandescent lamps were rapidly becoming more commonplace).

The earliest interior lights shining down on the statue were installed in 1926 and the first round of exterior lighting completed in 1929, although it was not until the early 1970s that the relatively soft, uniform illumination of the present system was perfected. It proved to be a resounding success, and the image of the grand temple glowing as a majestic beacon at night quickly became a worldwide icon — in fact, throughout the years, a distinctive subset of photographs has always been of the radiant memorial in the peak midge activity interval of early evening before full darkness.

PUBLIC OUTCRY. In stark contrast to the seven-year period during the 1980s, this time the National Park Service was inundated with highly emotional complaints from frustrated tourists, many of whom had an extremely narrow window of time set aside in their schedule to experience the classic view. Not unexpectedly, their wishes prevailed, and the elegant approach to the midge problem was dropped from consideration.

And so, the episode is archetypal not only on the efficient and cost-effective habitat modification level to which IPM practitioners have always aspired, but also on the reality check that so often throws cold water on those aspirations.

Curiously, Messersmith’s experiment has gained a peculiar sort of internet fame among business process specialists as a premier example — usually with the details somewhat mangled — of root cause analysis, a method of problem solving that focuses down on ultimate, rather than proximate, reasons for why things go wrong.

And for the time being, the Lincoln Memorial will still be dependent on cleaning to remedy its onslaught of legions of tiny, passionate and confused flies. For the most part, this is accomplished by power washing with low heat and pressure, about 160°F and 300-600 psi, which, although relatively innocuous compared to some past treatments, will still slowly grind down the marble over the years.

The author is an entomologist and former national IPM coordinator for the GSA’s Public Building Service in Washington, D.C.