Pests: Can’t We Just Kill Them All?

I escort spiders out of my house, use humane traps to relocate attic rats, and save honey bees from drowning in pools. Yet I’ve been known to hunt with a vengeance a mosquito that’s ruining my sleep, repeatedly buzzing in earshot in search of exposed skin. At such moments, I might push a button, if one existed, to rid the world of mosquitos forever.

However, recent press about disastrous blowback when humans target species deemed a nuisance should give pause to impulses to wipe out even the most bothersome of pests. Two examples. First, the 90 percent decline in the population of the monarch butterfly in the last two decades from spraying herbicide on genetically modified corn and soy in the Midwest, inadvertently destroying the milkweed on which the monarch caterpillar must feed. And second, the emergence of antibiotic-resistant bacteria from rampant misuse of antibiotics, both to treat viruses in humans and to fatten up livestock that aren’t sick. Consequently, people are at risk of picking up antibiotic-resistant superbugs when they’re hospitalized or even from eating meat.

Add to that the warning of scientists that land creatures are already undergoing a “sixth mass extinction” – the first to be caused by human activities like pollution and habitat destruction – which could eliminate up to two-thirds of all species by the century’s end. Man’s industrialization of fishing and global warming are putting marine fauna on the road to extinction too, according to a report just published in the journal Science.

Thus, recognizing my urge to annihilate mosquitos as potentially reckless, I wondered if a little understanding of the ecology of mosquitos might temper my hostility. What follows is what I learned about the niches of mosquitos and a couple other pesky critters.


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Credit: Holley & Chris Melton, FlickrCC

Houseflies are undeniably a nuisance as they carry many pathogens dangerous to humans, like typhoid, dysentery and tuberculosis. They feed by sucking up liquefied materials and are equipped to liquefy solid foodstuffs by adding their saliva or vomit. They consume whatever is available, from sugar to feces. Pathogens can be spread from contacting their body parts, vomit or feces.

Houseflies evolved some 65 million years ago and live virtually everywhere but the Antarctic. Females lay thousands of eggs which hatch into larvae (maggots) that feed voraciously for a week on dead and rotting matter – like feces, garbage or carrion – before forming a pupae from which the adult fly emerges.

Thus both larval and adult stages provide the vital service of cleaning up all manner of decaying organic materials and returning the nutrients to nature. Both also figure heavily in the diet of widely varied species, like lizards, birds and spiders. Given these easily appreciated contributions to ecosystems worldwide, humans have adopted a largely live and let live attitude toward houseflies, though few would advocate doing away with the flyswatter.

In fact, humans are looking to housefly larvae, with their yen for gorging on feces, to solve the problem of managing the huge volume of manure generated on pig farms. Pig waste is often spread on nearby cropland or forests after storage first in big lagoons, with potential for polluting both soil and water from the pathogens and excess nitrogen in manure. Scientists are tinkering with mass-rearing maggots in pig waste as an ecologically safer way to biodegrade it. What’s more, before the maggots transform into flies, they’re harvested as a protein source for animal feed.


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Credit: Sancho McCann, FlickrCC

When reflecting on blemishes to city sidewalks and parks left by humans, we’re likely to picture discarded food wrappings and cigarette butts. But if it weren’t for ants, our cities would also be heavily littered with the droppings from human foodstuff, everything from crumbs of bread, potato chips and cookies to blobs of sticky ketchup, mustard and ice cream.

According to urban ecologist Amy Savage of North Carolina State University, who is researching the fate of human food droppings in New York City, we owe a special debt of gratitude to “pavement ants,” so-named because they make nests in pavement cracks. These dark-brown/black ants function as mini garbage collectors, cleaning up our streets and parks in their tireless foraging for a meal. Using a technique called stable isotope analysis to see what an organism typically eats, Savage finds that most of what city-dwelling pavement ants consume is residue of human foods, as described in a January 2015 issue of Science News.

Though there are over 700 ant species in the United States alone, pavement ants are among the few which invade homes. Spraying indoors is not effective deterrent because it doesn’t prevent more ants from entering, according to the University of California’s Statewide Integrated Pest Management Program. Rather, the best strategy is to caulk all crevices they enter through and eliminate food spills right away.


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Credit: Ramón Portellano, Flickr CC

Mosquitos are considered the most dangerous insect to humans because they are vectors for transmitting infections like malaria, yellow fever, dengue fever and West Nile virus from person to person and credited with causing more than a million human deaths annually. Furthermore, with mosquitos it can feel personal when one is aware of being under attack or reminded later of the insult by the welt left behind.

Mosquitos have been around for at least 45 million years and, of the thousands of species, only some are bloodsucking. Bloodsucking types variably feed on mammals, reptiles, amphibians, birds and even fish, thus are vectors for animal diseases too, like heartworm in dogs and encephalitis in horses. Not all transmit diseases, however, and only the female sucks blood. The males feed on nectar so participate in pollinating plants. Research shows that mosquitos prefer people who are hot and sweaty, have type O blood or are pregnant.

Mosquitos live almost everywhere but the Antarctic. They are actually a type of fly so undergo the same lifecycle stages. Females seek stagnant water environments to lay eggs. The larvae remain in the water where they feed on and recycle microscopic organic matter. The larvae, in turn, are an important food source for a plethora of fish species including bass, bluegills, catfish, guppies, piranhas, salmon, tilapia and trout. Adult mosquitos are preyed upon by many insect-eating creatures including dragonflies, birds, frogs, lizards, bats, spiders and even other mosquitos.

From the perspective that, over the millennia, innumerable other species must have co-coevolved with and become dependent on mosquitos, one might assume that biologists would unanimously oppose mosquito eradication. Not so. Some biologists posit the world would get along fine without the disease-transmitting species. They envision only temporary disruption to ecosystems, as other insects move into vacated niches, and deem the potential for collateral extinction of other plant and animals species as acceptable risk.

This view is entirely anthropocentric and questioned by other biologists less comfortable with the inherent guesswork. They point also to evidence that the decline in one disease-vector mosquito species might just encourage another disease-carrying species to take root. There is, however, one point of agreement: Mosquitos are here to stay for the foreseeable future.

While learning about the contributions of houseflies and ants to sanitation makes me feel friendlier toward them, it’s doubtful I’ll ever conjure up amiable emotions when under attack at night by a bloodsucking mosquito. But I have eliminated standing water outside my house and repaired window screens to minimize such skirmishes. And, if a mosquito penetrates these defenses, I’ll just move to another room, because I never find the bugger anyway when I turn on the light.