Re: What makes crickets chirp at different speeds?

Hi Stephanie,
	
	Cricket chirping is the way different crickets talk to each other. The
most familiar cricket songs are those you hear on a warm night in summer. 
What you are hearing is male crickets calling to female crickets to let
them know where they are, hoping the female crickets will come find them.
These male crickets are only interested in females of the same species, so
to make sure that they are calling to the right females, different species
of crickets will have different calls.  If a female cricket hears the call
of a male of the same species, she will come looking for that male. If she
hears the wrong call, she will just ignore him.  

Male crickets will sing a different song when they meet other crickets.
When two male crickets meet, the two crickets will chirp at each other as
their way of fighting. Eventually one of the two crickets will run away
from the other.  When a male cricket meets a female cricket, the male will
try to impress her by chirping a different song.  By listening to the song
the female can tell if the cricket is healthy and “handsome”, or whether
the cricket is weak or ill.

	The songs crickets make are made by rubbing their wings together.  Each
time their wings rub they make a single note.  Crickets can’t really change
the notes of their songs the way a singing bird could.  The only way
different crickets can have different calls is to change the time between
chirps or to make some chirps louder than others. When the call of a
cricket is slowed down so that you can hear every individual chirp, you
will hear that some chirps are loud and some chirps are soft, and that some
chirps come very quickly while others come with pauses in between. As you
listen to crickets singing at night, it will sound like the crickets are
calling at different speeds, but what you are hearing is several different
species of crickets all calling together.  With careful listening and
practice, the different species of crickets can be identified just from the
calls they are making.

	The speed at which a cricket chirps will change depending on the
temperature outside when you listen to them.  Crickets, like most insects,
are ectotherms... this means that they are not warm bodied like us, but
instead are the same temperature as the air around them.  When crickets get
cold, they slow down, so on a cold night crickets will sing slower than on
warm nights.
 
You might think this would confuse the females, since they are only going
to listen for a particular call, but the females are usually just as cold
or as warm as the males and will listen for the call of a male at the same
temperature as them.  However, if the female cricket is warm and the male
cricket is cold, the female may not recognize that the male is the same
species. Instead it will be listening for a male cricket just as warm as
she is.

Notes:

I've tried to think of some good sources for further reading, though
unfortunately much of it is very technical and difficult to understand. 
One source I can recommend is the book "Introduction to the Study of
Insects" by Donald Borror, Charles Triplehorn, and Norman Johnson.  It has
some good general information on cricket behavior, including their songs,
and talks a bit about the different types of crickets.  

One of the experts in the field of cricket songs is Dr. TJ Walker at the
University of Florida. His web page is a good source for examples of
cricket songs... you can go to his page and get information on what the
crickets look like, what songs they sing, and where in the United States
they live.
 http://buzz.ifas.ufl.edu/crickets.htm

If you are curious how temperature can change a crickets song, the page on
the snowy tree cricket has samples of crickets calling on hot, warm, and
cold nights.
 http://buzz.ifas.ufl.edu/585a.htm