Posts Tagged ‘ecologist’

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By: Lindsay Hollingsworth

We’ve all seen them. The mosses creeping up foundations, the tiny leaves poking out from in between bricks, the young trees swaying merrily from their perches within gutters. And if you’re like me, you’ve probably taken secret joy in these tiny spots of green scattered throughout the city, even as those around you talk of untidiness and power washing.

While pursuing my master’s degree in Ireland, I had the opportunity to study these plants, hidden in plain sight in centuries-old stone walls. As I pursued my research, I learned that the scientific community has often overlooked wall plants as a point of potential ecological interest. Even as our understanding of cities as unique ecosystems has grown, wall plants and other urban botanicals remain a relatively underexplored topic. But there’s been just enough research done to give us tantalizing hints at a secret world of plants unfolding, like the frond of a fern, right under our noses – in the cracks and margins of our megastructures, and in the places that have become too ordinary to notice.

Wall rue (Asplenium ruta-muraria) growing on an ancient stone wall (Photo by Lindsay Hollingsworth)

Some research has suggested that, like forests, wall vegetation has successional stages. As city dirt accumulates and concrete and mortar weathered, walls are first colonized by lichens, then by mosses, and then by vascular plants. And as these tiny microhabitats form, wall plants provide shelter for insects and small animals, who in turn may carry seeds to new crannies and crevices. And in some cases, the unique environmental conditions of walls may provide a sanctuary for important local plant species, especially those that might normally make their homes in cliffs and rocky terrain.

It is unfortunate that we know so little about these plants, especially when we could learn so much from them. With so many of us living in cities, and more predicted to migrate to them in the near future, the question of how to make our cities more verdant and sustainable becomes increasingly crucial. 

And this question is perhaps especially pertinent to sprawling cities like Washington, D.C., where urban development covers so much of the surrounding landscape, and where there is an increasing push to incorporate green walls and roofs into our city infrastructure. Understanding the circumstances which allow plants to grow on walls without human aid may help us to more efficiently cultivate vegetation on our buildings. Currently, one of the biggest drawbacks to green walls is the expense and labor required to maintain them. However, better knowledge of what plants are naturally suited to wall colonization in a particular climate, and under what conditions they will do so, could help us better select plants that require little intervention to thrive. 

Green walls on an urban apartment building (WikiMedia Commons)

Moreover, an understanding of wall plants as not just a nuisance or a curiosity, but as an important part of urban ecosystems, may allow us to see and develop our green walls and roofs to support plants and animals beyond our cities. Green walls and roofs have already been deservedly celebrated for their ability to reduce air pollution, but the way in which animals seem to use naturally occurring wall plants for shelter raises some intriguing possibilities. Perhaps if we can explore the potential of green walls and roofs as refuges and habitat corridors, we could create fundamental changes to the types of animals that can use urban spaces. Perhaps instead of being obstacles for migrating songbirds and butterflies, they could be waystations. 

 The next time you see a cranesbill or hart’s tongue poking out from in between the stones of a garden wall or the bricks of the building, I encourage you to stop and take notice. Admire its fortitude, to grow in a place where so few can. Try and see what circumstances, what characteristics of this particular wall have made its small life possible. And remember that even in a city with no forests or fields, we live, always, side-by-side with nature.

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Lindsay Hollingsworth holds a master’s degree in Biodiversity and Conservation from Trinity College, Dublin, where she researched novel ecosystems, agroecology, and wall flora. She completed her undergraduate studies at St. Mary’s College of Maryland. She currently works at an environmental consulting company, and volunteers with the local Potomac Conservancy.

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By Mayda Nathan, insect ecologist

DC’s mosquitoes are enough to drive a person crazy. Abundant and stealthy, they make enjoying the DC summertime a real challenge, and they can transmit some nasty diseases, to boot. But they’re a natural part of this swampy environment, probably playing some underappreciated but pivotal ecological role, so we should accept their annoying presence at our barbeques and in our gardens…right? Wrong.

As an insect ecologist, I have a dark fascination with these maddening fellow residents of our city. Over the years that I’ve lived here, I’ve read about our mosquitoes, talked to experts, and participated in a local monitoring program. I’ve run into many misconceptions about who these critters are, what they’re doing here, and the ways we can protect ourselves and stay sane during the summer months.

Misconception #1: There’s just one kind of mosquito in this region.

In North America, we have about 200 species of mosquito. A very small fraction of those bite humans (and, of those that do, it’s only the females who do the biting). There are 30+ different species of “DC mosquitoes.” They all depend on standing water to reproduce, but the type of water they want varies – for some species, only saltmarshes will do, while others insist on ephemeral pools in woodsy settings. Some species prefer the sorts of little pools of water that us humans are great at (unintentionally) providing, like in the form of abandoned tires and clogged gutters. Those are the species we tend to encounter most often in our neighborhoods.

Misconception #2: Mosquitoes are a natural part of this region’s ecosystems.

Yes, there are native mosquitoes here, but most mosquitoes in your DC yard are relative newcomers to the regional ecosystem. The most abundant, irritating mosquitoes in DC neighborhoods are of one species: Aedes albopictus, AKA the Asian tiger mosquito. As its name implies, this species is not from around here. Accidentally imported to North America sometime in the 1980s, the Asian tiger mosquito has taken a liking to its new digs and is now found throughout eastern North America, even becoming the most abundant mosquito in some cities.

We also have several non-native Culex mosquitoes in our midst (though they don’t seem to reach the same aggravating densities as the Asian tiger). Additionally, we have a new arrival. In 2011, Aedes aegypti, the yellow fever mosquito, was discovered in Capitol Hill.

Misconception #3: Bats and other predators in DC depend on mosquitoes for food.

Wouldn’t it be great if we could conscript our bat, bird, and spider friends to wage war on mosquitoes, on our behalf? Alas, while this may be true in wetlands and boreal zones, there is very little support for this idea in urban settings.

Bats in the DC area, for example, are almost certainly not mosquito-eating machines, hoovering up thousands of mosquitoes every night. For one, the Asian tiger mosquito is a day-flier, so its odds of encountering bats are low. Secondly, our bats probably focus their efforts on more rewarding insect prey; mosquitoes are like flying celery sticks, compared to the winged cheesesteaks that are moths and katydids. This is likely the case for many predators in our region; they will eat a mosquito but would probably rather eat something else.

Misconception #4: There’s no environmentally friendly way to control mosquitoes.

I get it – some of our past efforts to control mosquitoes, in the form of large-scale wetland drainage and DDT spraying, had environmental repercussions that are haunting us still. But there are quite a few things you and your neighbors can do to keep from getting bitten, and even to reduce the number of mosquitoes around your house, that have minimal impact on other species.

Defense tip 1: Protect your skin.

There’s an endless array of products that claim to repel mosquitoes, but only a very small number have repeatedly been shown to be effective. I’m only advocating for products that have stood up to rigorous scientific scrutiny. The consistent winner is DEET, followed closely by picaridin (a synthetic version of a molecule found in pepper plants). Oil of lemon eucalyptus has been shown to be effective, but it must be re-applied more frequently than DEET (every 6 hrs v. every 10 for DEET). Also, throw out your citronella sprays and candles. That stuff’s useless.

Defense tip 2: Stagnant water is the enemy.

Start by removing ALL standing water around your house – what the pros refer to as “tip-‘n-toss.” Asian tiger mosquitoes can breed in amazingly small quantities of water, so no potential container should go overlooked. In my neighborhood, some common sources are:

  • Planter saucers.
  • Backed-up gutters.
  • Trash and recycling cans with broken or missing lids; submit a request through DC 311 to have yours fixed/replaced, and in the meantime, drill a small hole in the bottom.
  • Those accordion-style gutter extenders that direct water away from a house; pop a nylon knee-high over the end to keep the mosquitoes from going inside.
  • In-ground drain lines; secure a piece of window screening over the opening to keep mosquitoes out.

If your yard has a fountain or something similar that you can’t empty, pick up some mosquitofish (Amazon will ship you live ones!) or Bti dunks or Bti bits. These latter products contain a strain of bacteria that are toxic to mosquitoes and a few close fly relatives, but are harmless to everyone else – you, your dog, birds, bees, butterflies, etc.

Defense tip 3: Go on the offensive – but spray only if you must.

If removing standing water and using an effective repellent don’t keep the mosquitoes at bay, you still have a few options – from the passive to the nuclear.

  • Gravid Aedes Traps, or GATs. These nifty contraptions use water to lure in female mosquitoes who are looking for a spot to lay their eggs. There’s a big caveat: the traps are only effective if most contiguous neighbors deploy them. It won’t hurt if you’re the only one on your block who has GATs in your yard, but it won’t help much, either. On the plus side, areas with more than 80 percent of households using GATs have seen remarkable declines in mosquito numbers.
  • Some commercial spraying companies offer “natural,” “garlic-based” alternative to insecticides. This product doesn’t kill mosquitoes; it merely repels them. Online reviews are positive. But it is pricey and needs to be applied frequently.
  • Commercial spraying operations – the nuclear option. If you’re pregnant or expect to become pregnant, or have an infant or someone else in your household who’s immunocompromised – that is, if someone in your home is particularly at risk from mosquito-borne diseases like West Nile virus or Zika – then you might want to consider this option. It works, but it works because it’s a serious pesticide being applied to the vegetation and foundation around your house.

* In order to preserve insect biodiversity, consider making commercial insecticide treatment of your property a last-choice option. The treatment often involves pyrethroids – a group of compounds that are generally safe for mammals and birds (yay), and that don’t stick around long in the environment (yay), but that are highly toxic to a broad swath of insects (boo). For effective mosquito-killing power, pyrethroids are sort of the least-bad option, but using them will wipe out a lot of the wonderful, harmless insect biodiversity you might otherwise get to experience in your yard.

Go forth, armed with mosquito knowledge, to enjoy your porch beers, barbecues, and backyard play dates. Hopefully this information will help keep you sane and healthy all summer long.

Mayda Nathan is completing her PhD at the University of Maryland, where she studies insect ecology. She has lived in Washington, DC for ten years, and loves the city – mosquitoes and all.

 

 

 

 

Photo 1: Aedes albopictus, the Asian tiger mosquito – frequent crasher of DC picnics, barbeques, and gardening sessions. Photo credit: James Gathany, CDC. Photo is in the public domain.
Photo 2: Species like the little brown bat will eat mosquitoes, but they don’t eat them exclusively, and they’re unlikely to encounter the day-flying mosquitoes that plague DC yards and parks. Photo credit: “Healthy little brown bat” by Ann Froschauer, USFWS, CC BY 2.0.
Photo 3: Citronella candles have been shown to be totally ineffective at repelling mosquitoes. Don’t waste your money; buy some DEET, picaridin, or oil of lemon eucalyptus, instead. Photo credit: “Citronella Kerzen” by Joho345 CC BY 4.0.
Photo 4: Clogged gutters: a common mosquito breeding site in cities like DC. Photo credit: “Gutter clog” by Eric Schmuttenmaer CC BY-SA 2.0