Insects and the germs they carry
Project cost ($):
1 day to prepare, 5 days for the science project experiment
Access to laboratory equipment (eg. petri dishes)
Always follow laboratory safety guidelines and always practice sterile technique when handling microbes. Never have any food or drink at your workstation and always thoroughly wash your hands with disinfectant soap or alcohol before leaving your workstation. Always dispose of used material in a biohazard bag. If none are available, the bacteria should be destroyed with bleach before being disposed of. Knives should be handled under adult supervision.
This science fair project was done to determine the amount of germs carried by different types of insects. The experiment was done using ants, cockroaches, flies and beetles.
Flies and cockroaches have more germs on them than the ants or beetles.
Insects and diseases
Most insects carry bacteria, viruses and parasites on their bodies. When these insects come into contact with people or when they bite/sting, they leave behind many types of germs. Some of these germs cause diseases. Insects like mosquitoes, some species of flies, beetles and fleas spread diseases when they suck on the blood of a diseased person and then bite or feed on a healthy person.
Very few diseases are actually caused by the bite of the insects. More often than not, it is the disease causing microorganisms or pathogens that are passed on to people when they are bitten by the insects that carry these diseases.
Houseflies are known to carry millions of microorganisms on their feet. They pick up microorganisms when they sit on feces. These microorganisms are passed to a person when he consumes food and drinks that the house flies contaminate. This is how people contract typhoid and cholera. Cockroaches are also known to thrive in filthy environments and are very capable of spreading diseases. Mosquitoes are known to cause dengue fever and malaria. The Tsetse fly carries a type of protozoa that is known to cause "sleeping sickness".
Insects, germs, bacteria, virus, parasites, pathogens
The materials required for this science fair project:
- 4 petri dishes prepared with agar
- 4 plastic containers
- An ant
- A cockroach
- A fly
- A beetle
- Ensure that all of these insects are caught from the same general location - ie: if you decide to catch these in your garden, let it be only from your garden. Don't catch some of the insects in your garden, and the rest from your neighbors'.
- A ruler
- A stopwatch
- A clean pair of tweezers
- 1 marker pen
1. For this science fair project, the independent variable is the type of insect used – the ant, cockroach, fly or beetle. The dependent variable is the size of bacteria colony that grows in each petri dish. This is determined by measuring the approximate diameter of the colony with a ruler. The constants (control variables) are the room temperature, the amount of sunlight, the garden from which the insects are obtained, and the agar preparation.
2. The 4 petri dishes are filled with agar and stored in a refrigerator. The petri dishes are brought to room temperature before the start of the experiment. They are taken out of the refrigerator and allowed to warm up to room temperature. The 4 petri dishes are labeled “ant”, “cockroach”, “fly” and “beetle”.
3. An ant, a cockroach, a fly and a beetle are caught with the tweezers and kept in separate plastic containers. Once the petri dishes have attained room temperature, the insects are released onto the respective petri dishes and the plastic containers are closed with their covers. The insects are allowed to crawl all over the agar for 1 minute. After 1 minute is over, the cover of the petri dish is removed and the insects are released.
4. The petri dishes are then sealed with their covers and kept in a cool shaded place to allow the bacteria to grow for the next 5 days. The diameter of the bacteria colony growth is measured everyday for 5 days and the measurements are recorded in the below table.
The results show that the petri dishes exposed to the cockroach and the ant had more pronounced bacteria growth compared to the petri dishes exposed to the fly and the beetle.
||Diameter of bacterial growth (mm)
The graph below represents the results of our science experiment:
The hypothesis that flies and cockroaches have more germs on them is proven to be only partially correct. The cockroach and the ant had the highest amount of bacteria, followed by the fly, and finally the beetle.
When insects like mosquitoes bite and suck our blood, they inject some of their saliva into our skin to prevent our blood from clotting. This helps facilitate the feeding precess. This is how disease- causing germs enter our bodies- through the mosquitoes’ saliva. However, some insects like bees and wasps have stings that cause pain, but do not spread any disease.
The science fair project can be repeated by using other types of insects like dragon flies, bed beetles or spiders.
Try to repeat the experiment by capturing flies from various locations like a garbage dump, near animal feces, within the house, or in the garden and compare the amount of germs in them.
Also, have you considered the body sizes of the insects? Perhaps the cockroach has more germs than the ant because it has a larger body size and hence a larger surface area to carry microorganisms? A more accurate way to assess which insects are "dirtier" is to compare a certain quantity of insects that it takes to cover a certain surface area.
Insect borne diseases - http://www.traveldoctor.co.uk/insects.htm
Insects transmit germs - http://purpleslinky.com/trivia/science/insects-transmit-germs/
Insect borne-disease - http://www.watchtower.org/e/20030522/article_01.htm