July 31, 2014 Tiny and Deadly: The Mosquito
Of the conservative estimate of 10 million species on planet Earth, there currently exist 2,500 different kinds of mosquitoes. Yet despite being the size and weight of a grape seed, these are deadly and fearsome creatures. Mosquitoes are benefiting from global warming meaning once near-decimated strains of diseases like malaria are on the rise again. So how has something so tiny, yet so deadly, been able to successfully inhabit our planet for the past 80 million years?
It’s all in the size and, in this case, it matters to be small. Mosquitoes are adapted to every terrestrial ecosystem from the top of mountains to valley bottoms, from the Arctic Circle to the Sahara desert, and everything in between. They have thrived and adapted with the spread of human beings. In 300 years, the common house mosquito which started in Africa is now global.
The mosquito is a self-serving creature. She’s not an aerator of soil like ants or worms, nor a pollinator like bees or moths, and not an essential food source for a particular species. Her goal is to feed and breed. Mosquitoes and the pathogens that they carry are extremely hardy. They are clever and relentless critters. Our troubles with mosquitoes are getting worse as they infect and kill millions of people each year, despite all out war by modern science.
Within 15 minutes a female can lay about 250 eggs. One by one, they are symmetrically orientated head-first and placed in water into a craft that has a pointy bow. All 250 float together in a war canoe formation. Incubation takes about two days and then the larvae hatch. Much longer, segmented, wriggly, whiskered, with specialized air tubes for breathing, they are set to grow and move into their next stage of development. Under magnification, they are as gruesome as any sci-fi monster! About 14 days after birth, they possess wings for moving, jaws for chewing, large compound eyes for finding their victims, a long spear-like drill for cutting through skin and sucking blood, and fuzzy antennae for smelling victims or sensing mates.
Its wings beat at about 250 to 500 strokes a second and it can attain and maintain speeds of 5 km./hr. and, rather clumsily, hover.
Like humans, their appetite for sex is insatiable, so two days after they become adult they search for a mate. The process begins at dusk or dawn when hundreds or perhaps thousands of males form a dancing swam in the air near a landmark like a chimney or a church steeple. Males smell the females, lock together and copulate. In many cases the fit is so tight that the male has some difficulties escaping and an unfortunate few manage to get away only by leaving their sex organs behind.
The female mosquito needs just one other ingredient to nourish her eggs – blood. Mosquitoes sense with their antennae carbon dioxide and lactic acid as we exhale and other chemicals from our bodies. This usually occurs at ground level because our scent plume is heavier than air and sinks to ankle level. Next, their compound eyes, similar to a house fly, locate the unsuspecting victim. Lastly, the heat from our muscles guide them to the most radiant spot on our bodies – that bit of flesh not covered by clothing. She lands softly, probes skin up to 20 times with her long snake-like apparatus called a proboscis. Her salivary tube will deliver a chemical that inhibits the body’s ability to stop any bleeding that might begin. Ninety seconds later, her body weight is three times that before feeding, and in an aeronautical feat, she just manages to sputter away.
In one of nature’s most remarkable processes, within 45 minutes, she digests the blood by separating the water from the proteins and urinates pink droplets from her anus. The light solids are stored for creating future offspring. What she leaves behind from saliva will either irritate the skin or kill you! An old female mosquito may live for about five months.
Yellow fever, malaria, dengue, encephalitis and West Nile diseases have all, at one time or another, penetrated southern United States. Each pathogen carried by loathsome species of mosquitoes is excruciatingly painful and, in most cases, lethal. Malaria kills millions of people each year. DDT, although toxic to our environment, is still the only known effective mass antidote to curtail the spread of malaria.
West Nile disease, carried by the common house mosquito, has a relatively short history first appearing in Israel in the 1950s. It appears to follow flyways of migratory birds as vectors of the disease. Crows, ravens, jays and other Corvids are particularly susceptible to West Nile.
The Rocky Mountains in their entirety and parts of British Columbia are the only regions in North America not yet permeated by this disease. The chemical DEET appears to be an effective insecticide to ward off mosquitoes as does the natural chemical citronella, but it must be frequently reapplied.
Scientists from the University of Oregon have shown that the mosquito Wyeomyia smithii from Alabama and Florida has begun to use global warming to drive its evolutionary clock.
Instead of destroying this enemy, modern science is trying to genetically convert her. The race to find the genes to prevent pathogens from developing in mosquitoes is on. But in the meantime, human beings are perishing by the millions as mosquito diseases expand worldwide at an alarming rate.
Earth Dr Reese Halter is a broadcaster and biologist. His upcoming book is Shepherding the Sea:The Race To Save Our Oceans.
Text © by Dr Reese Halter 2014. All rights reserved.