While flies are filthy creatures that contaminate our homes with germs and diseases, sometimes they’re interesting to observe. How come they always seem to resurrect when you’re sure you’ve killed them? Are they immortal?
Flies don’t really come back to life after dying. If you continue having a housefly problem after exterminating them, they are probably different from the ones that died. People think flies come back to life because they can pretend to be dead when attacked and later spring back to life.
Facts and fictions
It’s always frustrating to exterminate flies and see them back in a matter of minutes. This leaves many people thinking that flies can come back to life. However, that is never the case. Flies can’t come back to life after they die. So what actually happens?
1. It’s probably more flies
After using a bug spray, a swarm of flies that appears again after some time are probably new, not the ones you killed. Flies are the most common domestic pests, and you can’t get rid of them entirely.
If whatever attracted the flies in the first place is still around (maybe some honey or rotten food), you can expect more flies to come from the surrounding area. Also, houseflies have a very brief life cycle, often less than a week. Therefore, their larvae take a very short time to develop into adults.
Some fly species are also outright scavengers, and their larvae will quickly emerge from trash or decaying matter. Female flies will start laying larvae eggs a few hours after attaining adulthood, depending on the species.
As a result, you might exterminate all visible flies but still have the same problem a few hours later.
2. They were probably playing possum
Like most insects, some species of flies can drop and pretend to be dead to avoid a threat. Although the common housefly is likely to use its fast reflexes to flee from a potential threat, some threats, like bug spray, are too quick to run from.
Feigning death, which scientists call thanatosis, happens in a wide variety of animals, including insects like flies. Sometimes it’s a natural reaction to threats where the fly loses mobility and goes into a stupor.
3. Not dead in the first place
Sometimes you might think you’ve killed an insect, only for it to start kicking again after a few minutes. On those occasions, the fly is not really dead; it’s just stunning.
Flies are resilient insects that don’t die easily. Therefore, smacking them with a magazine might not finish the job.
How do you know if a fly is really dead?
Since some species of flies can feign death, lying motionless does not guarantee you’ve killed them. If you want to confirm whether a fly is really dead, you can use a needle or a fine pin to move its maxillary or labial palps.
Dead insects cannot move when their palms are disturbed. So if the fly moves in response to your poking, it’s definitely alive. For example, dirty hair can attract flies. When you slap them, they may fall into the air and lay as if they are dead for a while. After some time, you will notice the same fly around your head.
Does salt bring flies back to life?
You’ve probably seen the “bringing a fly back to life magic trick.” If you haven’t, here’s how it works:
- Catch a living fly (however challenging that might be.)
- Drown the fly in a glass of water. You can submerge it for 10 minutes using a drinking straw.
- Sprinkle a bar napkin with just enough salt to coat it.
- Remove the “dead fly” from the water and wrap it gently with the salted napkin.
- Wait for several minutes while watching the salted napkin.
After 5 to 10 minutes, you and the crowd around will be shocked to see the napkin start to vibrate or bustle a little. Give it a minute or two, and unwrap the napkin. The fly will be back on its feet and will probably fly away.
So, what magical properties does salt have that bring a fly back to life?
When you drown a fly, it doesn’t die immediately. This is because flies don’t breathe through noses like humans. Instead, they use a series of tubes called spiracles. Therefore, water blocks the spiracles when you drown them, preventing them from breathing in but leaving enough air to keep them unconscious but alive.
As a result, salting the stunned fly helps absorb water from the spiracles, allowing it to breathe again. It will then regain consciousness and fly away.
Can a frozen fly come back to life?
If you freeze a fly long enough, it will die permanently and not come back to life. Freezing destroys most biological systems that have not evolved to adapt to it.
Surprisingly, no species of houseflies, including the Belgica Antarctica fly, has the coping mechanism for freezing temperatures.
During the freezing process, water is known to expand and solidify. Therefore, if you freeze an organism, ice crystals develop in its cells and could rupture the cell membranes.
Freezing also causes salts and ions to leave the solution of the innards of a fly and damages them in the process. Some of the growing cells might also experience physical damage.
They Can’t Stand the Cold
In extremely cold temperatures, flies go into a state of diapause, meaning their development and appetite are slowed until the temperatures are high enough to promote activity. As a result, most flies disappear in the winter and resurface when conditions are warmer.
That said, not all flies are cryophobic. Some species can actually withstand winter temperatures indoors. So, don’t assume your fly problem will end entirely because it’s winter.
However, there’s a difference between indoor winter temperatures and the freezer box. No species of flies can survive an hour in a freezer box due to the extreme temperatures.
Do flies hibernate?
Surprisingly, flies hibernate like bears. In fact, most insects hibernate during the winter to try and survive the freezing temperatures.
However, for flies and other insects, hibernation does not constitute sleeping for months in a cave-like bear, snakes, or skunks do. Instead, they spend their winters in a state of diapause.
What’s the difference?
Hibernating animals like snakes and bears eat and fill up during the fall so that they can sleep during the winter. In winter, these animals are just sleeping (you can even wake them up), only that the sleep is deep and longer than usual. Their bodies still function as they would when they’re active; therefore, they continue developing and aging.
Animals in a diapause like flies and other insects are not asleep. They’re usually unconscious (so you can’t wake them.) Their bodies reduce metabolic activities such as appetite and development, so they remain as they are throughout the season.
When spring and temperatures are friendlier, flies leave the diapause and start moving around again.
Flies are fascinating insects, but they’re not immortal. If you kill a fly and see it come back to life, it was probably not dead, just unconscious. It could also have been pretending to be dead. Although some species of flies can withstand winter temperatures, no fly can survive in a freezer box.