Male and Female Flies

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

Wife: What are you doing?

Husband: Hunting Flies.

Wife: Oh! Killing any?

Husband: Yep, 3 males and 2 females.

Wife: How can you tell which are female and which are male?

Husband: The 3 flies were on a beer can and the 2 flies were on the phone.