Since they represent ideal breeding stock, they aren't spayed or neutered. (dogcare.dailypuppy.com)
Step 1: Forever moist and full of dark nooks and crannies, a kitchen sponge is ideal breeding ground for all kinds of harmful bacteria. (styleathome.com)
Ayala believes that this may have happened as recently as 10,000 years ago, when humans settled down and started farming; at that time, irrigation and huts would have created ideal breeding grounds for mosquitoes to help the parasites spread. (sciencemag.org)