"Some insects, specifically most species of the Hymenoptera, do things differently, with a sex determination system called haplodiploidy.
Males are always haploid, having only one set of chromosomes, and they produce only one kind of gamete, and all of their gametes are genetically identical. Females are diploid, and produce haploid eggs.
If the eggs are fertilized by a male, they develop into females; unfertilized eggs develop into males. Fathers can only have daughters, and mothers produce sons without the contribution of a male. Males don't have fathers, literally."
Read more in "Clone war of the sexes." By PZ Myers. Pharyngula, 01 Jul 2005.