UDP data format

so I am using an external system to send IQ data over UDP to the USRP
for transmission. I am trying to figure out how to format the data
before sending to USRP.

I printed out the result of gr.sizeof_gr_complex and found out a complex
sample is 8 bytes. (side question: why is it 8 bytes/sample when the
data that is sent over USB is 4 bytes/sample??)

the program i am using to send UDP accepts data input in string format,
so I have to break down the IQ data into byte integers, and then into
byte characters. How do i order the data, is it just IQ interleaved?
Little or big endian?