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Q: Flies won't fly ( Answered,   5 Comments )
Subject: Flies won't fly
Category: Science > Biology
Asked by: yagazuzy-ga
List Price: $5.00
Posted: 22 Jun 2006 04:03 PDT
Expires: 22 Jul 2006 04:03 PDT
Question ID: 740164
Short version: Why do flies sometimes not fly, even when threatened?

Long version: This morning when I got into the shower, some flies that
wouldn't fly away were just sitting there on the wall, so I began to
kill them.  Strangely, they didn't fly away even when I was killing
them.  They just sat there, sometimes crawling around the wall, while
I smashed them.  Some of them even got washed down the drain alive. 
When I discovered the sheer number of them, I stopped killing and just
took my shower.  When I finished, they were still there not moving! 
If I wanted to, I could smash each one of them, and they would barely
move to escape.  What causes flies to behave that way?
Subject: Re: Flies won't fly
Answered By: alanna-ga on 22 Jun 2006 12:29 PDT
Hi yagazuzy-ga -

Flies do not fly if the surrounding temperature is too cold for them
to move or if they haven't had time to build up the internal
temperatures needed for flight.

Unlike mammals, insects can't maintain  steady internal temperatures
on their own. They depend on the surrounding temperature to get enough
heat to operate their internal and external functions. Flies usually
get their heat boost from the sun, but sometimes they shiver or
vibrate their wings to elevate their internal temperatures.

Thermal Biology of Flying Insects

Insects can also become infected by parasites that inhibit their
ability to fly. They act listless as if they have a fever.  There is
even an evolutionary advantage to being helpless.  While the infected
insect may be killed off easily, other (uninfected) insects in their
community  can escape. The house fly is one of the insects in which
so-called "behavioral fever" has been shown. (It is even referred to
as "suicide.")

Behavioral Modifications in Insects...

My guess is that the flies in your shower--probably sitting on cold
tile--were just too cold to get started.  They had enough heat in them
to crawl, but not to fly. They appeared to "not care," but they were
probably in a sort of cold-induced "coma." But we can't rule out the
theory that they were infected with "behavioral fever."

Below are some websites that may interest you.  "On Six Legs"
describes cluster flies, a type of insect that spends the winter in
attics in large numbers.

Cold Blooded

On Six  Legs

Thanks a lot for using Google Answers.

All the best,


Request for Answer Clarification by yagazuzy-ga on 23 Jun 2006 12:18 PDT
Hi Alanna,

Thanks for the response.  It's definitely not the temperature since we
are in the middle of New York summer heat, and we don't have an air
conditioner in the apartment (and the fact that the flies still
wouldn't move after a hot, steamy shower!).

I also found some articles on cluster flies, but I don't think that's
it either since it is summer and they don't look like cluster flies
(their wings are separated while resting).  They look like normal
house flies.

I did notice something else since my first post.  The flies were gone
that night, but the following morning they were there again in the
bathroom not moving!  So, I think it is unlikely (not impossible I
guess without really observing some more) that they are infected,
seeing as they left and either the same flies or a different group
came back.

Do you have any other ideas/explanations?  Do flies sleep at night? 
Even so, would that explain their behavior?

Request for Answer Clarification by yagazuzy-ga on 23 Jun 2006 12:34 PDT
Also, I just found this article, which supports steph53's claim that
houseflies lose their ability to fly in old age:

However, I will ask my roommates if anyone killed the flies while I
was gone, but I don't think that's the case since there are not
smashed bodies on the walls (and the presence of a couple really old
smashed flies would indicate that no cleaning would have been
performed).  I will also try to motivate them to fly if I see them

Clarification of Answer by alanna-ga on 23 Jun 2006 22:21 PDT
Ah...the plot thickens.  Actually I wasn't disputing steph53's
observation that aged flies slow down and was interested to see the
paper on the possible biochemical mechanisms behind this.  I was just
looking for a reason why YOUR shower flies laid over and played dead. 
I discounted  aging as a reason for the flies to stop flying, because
it is unlikely that a whole swarm of flies are aging at the same rate.
Now that you tell me that the same think happened the next day, I can
more certainly rule out aging.  Yours are just random flies that are
swooshing into your apartment for some reason, then acting sleepy. 
(By the way, insects don't sleep but become inactive if the ambient
temperatures are too low as I mentioned in my original answer.)

However, now that I know you're in a New York apartment, I think I may
have a better clue as to why.  Has your building had a visit by the
exterminator recently? Or has insecticide been used by a neighbor? If
so, the flies could be drunk with poison, but not killed by it.

I believe I have given you the likely explanations for the phenomenon
you described in your question.  Perhaps you would also like to talk
to an entomologist (insect expert) at the American Museum of Natural
History.  The telephone number of the Entomology Department is
(212)769-5601. >
Subject: Re: Flies won't fly
From: probonopublico-ga on 22 Jun 2006 04:48 PDT
They like you and your place and they are prepared to put up with
beatings and your general bad behaviour, if it pleases you.

And why not?

You have been good enough to provide them with free board and
lodgings, so, even with all your faults, they see you for the nice guy
that you really are.
Subject: Re: Flies won't fly
From: steph53-ga on 22 Jun 2006 08:48 PDT
Probono is just joshing you :)

The real reason that your flies don't fly away could be that once
flies get too old ( they only live for a few weeks )they lose their
ability to fly or even move fast.

So you see? You have a (Fly ) senior citizens home in your shower ;)

And shame on you for murdering the poor old things..LOL

Subject: Re: Flies won't fly
From: brix24-ga on 23 Jun 2006 16:50 PDT
Could they be newly emerged flies (from the pupal stage)? However, I
don't know if they would emerge so synchronously. The wing condition
might be a clue.

"Newly emerged flies have shriveled wings and are usually pale and
soft-bodied. They do not acquire their typical colors and shape until
they have had sufficient time to dry and harden. The soft-bodied
condition of newly emerged flies aids them in working their way
through crevices in the soil. Newly emerged flies can easily reach the
surface after being buried under 1 to 4 feet of moderately packed
Subject: Re: Flies won't fly
From: probonopublico-ga on 24 Jun 2006 00:18 PDT
They probably need The Kiss o' Flyf.

Please try and report back.
Subject: Re: Flies won't fly
From: myoarin-ga on 24 Jun 2006 01:26 PDT
OH, that's terrible, Probono!

Brix, the flies would not have been pupae on the walls of your shower  - I hope.

That is unless  - and this was something that occurred to me when I
first read the question -  you seldom clean the walls, with the
thought that maybe the adult flies ate something there that reduced
their mobility.
BUT I am not suggesting that.  ;)

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