The sound of flies moving around your ears can be very annoying, and I think our pets feel the same way because you will see them doing all they can to get rid of the discomfort the fly may be causing.
Apart from causing discomfort, flies cause a lot of other problems. In today's publication, we will be considering, the screwworm fly.
Screwworms are fly larvae, and they feed on living flesh, they infest all mammals and sometimes birds. Screworm myiasis is caused by two different species of flies, we have new world screwworms known as, "Cochliomyia hominivorax" and old worm screwworms known as, "Chrysomya bezziana".
New world screwworm was described first in 1857, it was found to infest humans on Devil's Island in French Guinea. It has been proven through studies in certain areas, that it is the most damaging insect parasite of livestock.
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With a good skill of high productivity, several clutches of eggs can be laid with new world screwworms, covering a generation of an entire lifecycle to be as short as two weeks.
Gravid female flies are naturally attracted to injury, I mean in all and every form that they come, eggs are then laid around and in the borders of such wounds.
After the eggs have hatch, the larvae begin to feed on live body tissue. As the maggots feed, the wound gets enlarged, creating a more attractive site for other female flies to visit and even creating a situation of secondary infection. Without prompt treatment, the affected animal would most likely die.
Thankfully, we now have suppression and eradication programs to tackle screwworms, but before then, the spread was great. Injuries that are infested by screwworms usually attract other female screwworms, creating a situation of multiple infections.
After feeding through the molts, the larvae would leave the wound and fall off to the ground, they would proceed into the soil to pupate, and the adult that emerges afterward feeds on wound fluids and mates after 3-5 days.
The female flies mate only once, but they can lay more than one batch of eggs at intervals within a few days. Female screwworms are attracted to all types of warm-blooded mammals, a fly may travel as far as 10-20km in a tropical environment with a high density of animals, some even go up to 300km just in search of a new host.
Screwworms can infest different types of wounds, infestations are more common in the navel of newborns and vulval and perennial regions of their dams. In a case where an egg deposit is made on a mucous membrane, the larvae may enter into any orifice including the nostrils, mouth, ears, genitals, eyes, and sinuses.
It is usually difficult to detect the presence of infestation within one to two days after it has occurred, most likely after some time, only slight motion may be noticed inside the wound. As the larvae continue to feed, they will expand and deepen gradually.
After a few days, discharge and a distinctive odor follow suit. Other species of flies that usually feed on dead and decaying tissues can also take advantage of the situation and infest the wound.
For prevention, farm owners must ensure that vehicles entering their farms are sprayed with insecticide to prevent the entrance of screwworms and other flies into the farm. Some injuries can be treated surgically, most cases are treated with a suitable larvicide and allowed to heal without closure.
Remember that, humans can also get affected by the disease, also affecting the eyes, nasal or frontal sinuses, mouth, or ears.
References.
https://www.sciencenews.org/article/flesh-eating-screwworms-flies
https://www.nature.com/articles/s41598-020-77541-w.pdf
https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwwormJ