I think we are inadvertantly killing off all our flea predators through modern gardening routines.
I'm no hippy. But I have taken up organic gardening principles as of about 14 months ago and have noticed a reduction in unwanted pests of all varieties in that time. Removing all pesticide and herbicides from my garden has resulted in what I feel is a return to a natural balance, where no one species of creature is allowed to profligate to pest proportions.
I'm not talking extremes here just a few changes:
1) Remove all chemicle fertilisers, these feed your plants/grass but do not enrich your base soil and underlying eco systems. Think bright green grass but everything dead underneath, including good and bad bacteria/fungus/organisms
2) Remove all chemicle pesticides, these kill off way more than the bad guys, and may remove your friends (ie. those predators who would normally eat fleas/mosquitoes/ticks etc)
3) Add natural organic material to your gardens and lawns by means of compost. This is a one off application and only necessary if you normally remove your grass clippings, in order to add good bacterial and fungal communties to your lawn/gardens.
4) Add organic material to your lawn by removing your lawn mower catcher and letting the clippings be reinvested into your lawn. Bacteria and fungus underground will love these clippings, worms will love the extra bacteria to feast on, and I'm sure nematodes will multiply and feast on the fleas etc, creating a more balanced environment.
5) Lift your mower to its highest setting, ensuring a nice long healthy lawn with a nice healthy sub system going on underneath.