Opossums breed twice a year, and can have a litter as large as 13 babies. The babies live in the mother's pouch for about 50 days then cling to the mother’s fur for another 3 months. Opossums are nocturnal and omnivorous. They will eat rats, mice, young birds, insects, crustaceans, frogs, fruits and vegetables. Pet food and garbage left out overnight will attract opossums.
Opossums normally live in hollow trees or logs, but will live in woodpiles, rock piles, under buildings and in attics. Since they do not dig very well they will inhabit burrows made by other animals.
When encountering humans opossums may hiss, sway and drool, this doesn’t mean the animal is rabid as it is a normal defense mechanism. Just leave the opossum alone and it will eventually leave. Opossums will also "play dead" if confronted by household pets and humans.
Opossums can generally be encouraged to leave the attic or underneath a house by playing a loud radio and putting bright lights near the nest site. With opossums it is better to play the radio and lights in the daytime so that they will leave at dark.
Once the opossums have left, repairs can be made to the area where they entered the residence.
More information can be found on the following websites:
Mammals of Texas (Virginia Opossum)
Texas Parks and Wildlife