Why all the flies?

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Why all the flies?

By Lee S. Yudin, Ph.D.
Pacific Daily News
January 31, 1998

God made the Fly and Forgot to tell us why – Ogden Nash

We all have endured a lot of stress since Typhoon Paka – power problems, water problems, and too many children not at school problems. And if these conditions weren’t enough to add a few more gray hairs to the top of one’s head, we now have to deal with an increasing number of pesky flies.

Flies are a very significant and divers group of insects. They include such fly pests as the filth flies (house fly, dung fly and green bottle fly) that feed on decaying food and fecal material, fungus gnats that dine on decaying organic matter and those pesky mosquitoes who nourish themselves on our blood by piercing the skin with their needle-like mouthparts. Filth flies, fungus gnats, and mosquitoes thrive in conditions where food is abundant and breeding sites are ideal to produce a vast number of offspring.

Typhoon Paka provided a tremendous amount of food and breeding sites for fly populations to dramatically increase. Food – in the source of garbage, decaying plant material, and rain – furnished a unique habitat for these flies to become a very big nuisance on Guam.

Flies go through four stages of development: egg, larva (often called maggots when referring to flies), pupa and adult. Adult filth flies are very attracted to garbage and animals droppings from chickens, dogs, goats and pigs to deposit their eggs in. A true but sad fact is that the number of filth flies in your neighborhood is highly related to the number of breeding and feeding sites it contains. Simply stated, the greater amount of garbage the greater amount of flies. Anyone who has ever been to Ordot landfill knows this lesson too well.

Paka took the garbage commonly stored outside our homes and spread it all over the island, allowing Guam to become a breeding ground for these particular filth flies. Filth flies can also carry certain pathogenic organisms that can cause certain illness in humans.

In the tropics, the decomposition process starts very quickly as dead trees, up-rooted shrubs and broken limbs lay on the ground. This process of decomposition is partly due to fungal activity. Fungus gnats reproduce in moist areas in decaying organic matter such as leaf litter. More food means a greater number of fungus gnats. A few weeks after Paka, there was an explosive number of fungus gnats on Guam. Their breeding sites are anywhere organic matter is decomposing. As adults, gnats have the ability to fly and seek out more breeding sites fro their offspring. Fungus gnats are attracted to lights, and due to their very small size can easily go underneath doors and through most window screens as they enter our homes. They do not bite; however, they can become a real source of irritation as they fly into our food, water, eyes and hair.

Paka also brought with it a great deal of rain. Areas of land that were dry before Paka are now filled with water. Containers of all shapes and sizes were filled with water as well. Unlike the filth flies, the mosquito’s larvae are aquatic (i.e., develop in pools or containers of standing water). The more standing water, the greater number of breeding sites can be used by the females to lay their eggs. What easy targets we humans become after typhoons when we purposely keep our windows open to allow the air to circulate throughout our homes. Here is a simple equation: excess rain water + actively feeding female mosquitoes + human blood = more and more mosquito pests.

Sanitation is the best way each of us can help our community reduce the fly population. Garbage needs to be picked up around everyone’s property and placed in sealed bags for garbage pick up. Garbage cans should have a tight-fitting lid that will not be blown off by wind or come off if the can is knocked over by dogs or cats. Disinfectants should be used periodically to clean the inside of garbage cans. Animal litter must be properly buried to reduce breeding sites for filth fillies. Excess water found in buckets, jars, and old tires must be emptied. You may want to install screen doors. Seal cracks or other entry points through which flies may enter the house. When you see a fly inside the house, use a good old-fashioned fly swatter. Remember, a dead fly cannot breed.

Lee S. Yudin is an entomologist at the University of Guam.