Insects - Flies

Insects - Flies All insects are an integral part of our ecosystems. As part of food chains, insects provide sustenance (dinner) for countless other animals. For instance, just one crow can eat as many as 16 bushels of insects in one year. So--all insects are beneficial and necessary. It's just that with some insects--like flies--it's harder to remember that they are a necessary part of the world around us.

There are more than 100,000 different species of flies. They are found everywhere in the world--even in Antarctica. They belong to the order of insects called Diptera which means "two wings". Most insects have 4 wings. On the bodies of flies, however, over time, this second set of wings developed into small knobs called halteres that are located behind their main wings. These knobs help keep flies steady and balanced when they fly and make them very agile. They can maneuver themselves into intricate flight patterns, they can hover and spin, and they can even fly backwards.

Like all insects, flies have 6 legs and segmented bodies consisting of a head, a thorax and an abdomen.

Flies have hairy, sticky feet and are able to walk upside down. Their special feet enable them to land on smooth surfaces (like your wall) and not slide off.

Flies lay their eggs in soil, on plants, on the bodies of other animals, and frequently on dead or rotting flesh. Fly larvae are usually called maggots.

Different flies dine on different foods. Flies around the world eat nectar, plant sap, blood, other insects, and decaying matter. Did you know that a mosquito is actually a type of fly? Of the species of flies that eat blood, only the females are the blood eaters. They need the nutrients in blood to be able to lay eggs. The males of these species usually dine on nectar from plants and flowers. The species of flies that we call houseflies like to eat OUR food!

Flies cannot chew. They have to suck up their food. Flies have mouth parts that absorb food like a sponge. Their food has to be in a liquid form in order for them to eat it. They have a tongue shaped like a drinking straw to slurp up their meals. Flies that eat nectar or blood do so by using their tongue which is called a proboscis. Even flies that eat other insects do so by sucking out the insides of their victims. When a housefly lands on our food, it vomits on the food. The digestive juices, enzymes, and saliva in the vomit begin to break down and dissolve the food. The fly can then suck up the liquid food with its sponge-like mouth parts and its proboscis. If flies eat food from garbage cans or any other source of germy food, some of those germs stick to the fly's mouthparts and when the fly vomits on its next snack (your sandwich?), it transfers some of those germs.

Houseflies spread germs in other ways, too. The trouble is-- houseflies breed in and around manure piles (manure is the big, wet, warm droppings of cows, sheep, horses, and other large mammals), garbage, and rotting flesh. All of these places provide a good source of food for the maggots when they hatch. Flies have sticky pads on their feet, and every time a fly lands on something in our home and walks around on it, it leaves behind little bits of manure, garbage, or rotting flesh. When they walk on our food or our countertops, they leave behind germs from the last place they visited.

Housefly maggots can hatch within 24 hours if the place where the eggs were laid is warm and moist.

A fly has taste receptors on its feet so it can tell if something is good to eat as soon as it lands on it.

Flies can spread typhoid fever. During the Spanish-American War in 1898, typhoid was spread by flies and killed over 5,000 soldiers. The battles themselves in this war only killed 4,000 soldiers! Flies also spread malaria, yellow fever, sleeping sickness, and dysentery.

They do have their beneficial side. They help control other insect pests. They act as scavengers and recylers when they feed on decaying waste such as dung and dead animals. Of course, they serve as food themselves for other insects and many birds. Flies are also great pollinators. Only bees and some wasps pollinate more plants and flowers than flies.

Flies are a favorite snack for many spiders. So if you don't like flies in your house, encourage spiders to move in.

The Fly Life Cycle

Female houseflies do not lay their eggs all in one place. They use various locations so that a predator will not eat all of their eggs.

What are the 4 stages of the life cycle of a fly? (It's the same 4 stages that all insects go through).
In 2 weeks, how many eggs can a housefly lay?
List the places where houseflies commonly lay their eggs.
In warm weather, how long does the egg to adult cycle take?
Scroll down to the bottom of the page and list some ways to keep flies from breeding around your home.

House Flies

Houseflies have large compound eyes. Compound eyes cannot be focused--so flies see everything as a blurry image. However, compound eyes see things very quickly. Flies can immediately detect even the slightest movement. This gives them a chance to escape from predators. It is also why it is so difficult to hit them with a flyswatter.

About how long does a house fly live?

Diptera

What kinds of flies show up in our homes?�. Houseflies, of course. Fruit flies and bluebottles also fly in to sample our cuisine.

You don't usually see any flies in the wintertime. Then, all of a sudden, they appear when the weather is warm. If you live in a place where it is cold in the wintertime (like Utah), where are all the flies?

Ohio State University Extension Factsheet

Female horse flies feed on blood. They have a substance in their saliva that keeps blood from clotting so that they can continue to freely feed. Vampire bats have a similar substance in their saliva because they also feed on the blood of mammals.

We think that WE are bothered by flies! The flies on this page are horse flies. What other animals (besides horses) do they torment?
Horse flies are big! How big?

Fly Information

At your next family picnic when flies are buzzing around your aunt's potato salad, casually mention that scientists have estimated that houseflies carry around 1,941,000 different kinds of bacteria.

What purpose do the hairs on a fly's body serve?
How do flies keep their eyes clean?

Information About Robber Flies

Robber flies are pretty cool. They eat other insects. They station themselves on a perch like the limb of a tree of plant. When an insect flies by, the robber fly zooms out and grabs its prey with its strong legs. They have to be very good flyers to be able to do this. Then it stabs its dinner with a piercing mouthpart, injects special poison-like enzymes, and returns to its perch. The poison turns the victim's insides to liquid (Remember--flies have sucking mouths and have to slurp up their food). The robber fly then sucks the insides out of the sweet ladybug that it snatched. Robber flies have hairy faces which help protect their eyes from the prey that they catch. Some kinds of robber flies hide on the ground and catch insects that are crawling by.

Check out the goofy illustration on this page that shows robber flies holding up a bug stage coach!
How are robber flies beneficial?
From the menu on the left of the page, click on "Foraging". You can see a photo of a robber fly waiting looking for its dinner and a photo of a robber fly capturing its prey in flight. After a robber fly catches its meal, where on the victim's body does the robber fly inject the enzymes?

Blow Flies and Bottle Flies

Blowflies are larger than houseflies and are usually metallic blue or green.

If a garbage can is left unattended, how many blowflies can it produce in a week?

Blow Flies and Flesh Flies

Flesh flies lay their eggs in the bodies of dead animals. They particularly like to lay eggs in nostrils because then the larvae don't have to travel through fur to find good places to feed.

How are blowflies and flesh flies beneficial?

Sheep Blowflies

Blowflies often lay their eggs in open wounds. When the eggs hatch, the larvae feed on pus. During World War I, doctors used blowfly maggots to help heal the wounds of soldiers. They actually raised these maggots for use in hospitals.

Describe the life cycle of a sheep blowfly and where each of the metamorphic fly stages spends its life.
Describe the effects of this fly on the sheep.

Ohio State University Extension - Stable Flies

Some plants eat flies (and other insects). The sundew plant grows in marshy areas. Its leaves are covered with sticky arm-like tentacles. A sweet nectar covers the leaves, and when flies land on the leaf to eat the nectar, they become trapped. The tentacles then surround the fly and produce special juices to digest it. A venus fly trap works in a similar way. It has 2 hinged leaves that also produce a sweet nectar. When an insect lands on a leaf, it may touch a fine trigger hair which makes the leaves snap shut, trapping the bug. It is then digested by the plant's juices.

Why should your dog be worried about stable flies?

Warbles of the Tree Squirrel Bot Fly

Stay away from botflies! One species of botfly uses mosquitoes to do their work for them. They catch a mosquito and glue a cluster of 15-20 eggs on its body. When the mosquito lands on you to bite you, the warmth of your skin makes the eggs hatch immediately. The larva of the botfly then burrows into your skin. Botflies use mosquitoes to do this same thing to other mammals as well as birds. Another species of botfly lays its eggs in the nostrils of mammals such as horses or deer. When the eggs hatch, they live on the blood of the host animal. One kind of botfly especially likes horses. It lays its eggs on the hairs of the horses legs. The eggs stay there until the horse licks itself. If the eggs get on the horse's tongue, they hatch immediately. The larvae burrow into the horse's tongue and live there for about a month. Then they burst out of the tongue and are swallowed and live in the horse's intestines. They are eventually expelled through the horse's droppings as pupae that develop into adult flies, and the cycle begins again.

Yikes! Describe the life cycle of this rodent botfly that laid its eggs on a poor squirrel.

Syrphid Flies

Hover flies are sometimes called flower flies. They are brightly colored and look a lot like bees and wasps. The feed on pollen and nectar.

Check out this photograph to see how much a hover fly looks like a bee.

Black Flies

Black flies and other biting insects find their prey by the smell, warmth, and carbon dioxide that the mammal gives off.

What disease can blackflies transmit to humans?
Scroll about halfway down the page to see a good photo of the compound eyes of a blackfly.

The Scientific Way To Swat a Fly

Practice makes perfect.

Some people are very serious about hitting a fly with every swing of the flyswatter. When is the best time in the fly's flight pattern to hit it?

Midge Biology

(On the left, scroll down to find midges under "Other Important Species".)Midges are tiny flies. They fly in huge swarms, usually in the evening, and are often seen nears ponds and streams. Their larvae live in damp places or in water and feed on rotting plants and algae. One type of midge is one of the few insects to live in the Antarctic.

What are the red larvae of some midges called?
What beneficial role do they play?

Close Up

We have midges in Utah.

Scroll down to the bottom of the page to see a close up of the head of a biting midge. You can clearly see its proboscis. A midge has serrated teeth (serrated means notched on the edge like a saw). A midge uses these serrated teeth to saw through a little piece of our skin. Then what does it do?

Bibliographies help the end users "read more about it"...or in other words, find further information. They also give credit where credit is due.

Bibliography

Fischer-Nagel, Heiderose and Andreas. The Housefly. Carolrhoda Books: Minneapolis, 1988.
Greenbacker, Liz. Bugs: Stingers, Suckers, Sweeties, Swingers. Franklin Watts: New York, 1993.
Hunt, Joni Phelps. Insects. Silver Burdett Press: Parsippany, New Jersey, 1995.
Johnson, Jinny. Children's Guide to Insects and Spiders. Simon & Schuster: New York, 1996.
Miller, Sara Swan. Flies. Franklin Watts: New York, 1998.
O'Toole, Christopher. Discovering Flies. Bookwright Press: New York, 1987.
Watts, Barrie. Fly. Silver Burdett Press: New Jersey, 1991.

Author: LINDA MOSBACKER - Email linda.mosbacker@slc.k12.ut.us