Sex Sells But (telling the) Sex (of) Flies?

A woman walked into the kitchen to find her husband stalking around
with a fly swatter

"What are you doing?" she asked.

"Hunting Flies" he responded.

"Oh! Killed any?" she asked.

"Yep, 3 males, 2 females," he replied.

Intrigued, she asked, "How can you tell them apart?"

He responded, "3 were on a beer can, 2 were on the phone.