One advantage of a tarantula as a pet is that it is so easy to feed. All tarantulas feed on living animal foods, generally insects and other invertebrates that wander too close to the burrow opening at night and touch the “trap” line of silk. When the line is vibrated, the spider decodes the characters of the vibration as either food or a predator. If food, it waits until the insect comes close enough for a fast jump to allow it to grab the prey, inject it with venom, and then (usually) cover it with silk and start external digestion. If the spider finds a cricket while moving around the cage at night and the cricket freezes, the tarantula may not even recognize it as food. As a rule, if you place dead crickets in the terrarium, the tarantula will ignore them.
The normal food of pet tarantulas is the domestic or brown cricket (Acheta domesticus). This insect is raised by the millions (perhaps billions) on cricket farms across the country and is sold in most pet shops, through the mail, and over the Internet. Crickets are cheap and are a good food for tarantulas. Remember that the roughage of an insect is not the problem it might be when feeding it to a reptile: the spider eats only the liquefied soft tissues.
Crickets should be well fed themselves before being offered to a tarantula. You can use commercial cricket foods, a leaf of green lettuce, some shredded carrots, or unsweetened cereal—all are accepted. Give the crickets water in a small soda-bottle cap or in the form of small cubes of white potato or orange. Try to make sure the crickets have eaten before you feed them to the tarantula. No one seems to have any idea just what a tarantula needs for full and proper nutrition, but it certainly doesn’t hurt to make sure its prey is healthy and well fed.
You can also occasionally feed mealworms (available in many sizes for almost any tarantula), waxworms, small Madagascan hissing cockroaches, and other cultured insects. Wild insects such as grasshoppers, dragonflies (with cut wings), and moths can be used as food, but you must be sure they are not carrying high levels of pesticides, herbicides, or fertilizers in their bodies and that they are not contaminated by heavy metals found near highways. Large beetles are generally avoided as food, as are wasps and ants of any type. Flies probably are contaminated, as are household roaches, but cultured flightless houseflies (sometimes sold as bungee bugs) and roaches are excellent foods.
Tarantulas eat other foods such as millipedes and centipedes (obviously the largest ones can be dangerous because of their toxins and their bites, respectively), scorpions (though they may be risky from several aspects), small mice (which make a bloody mess and are not recommended), and—if waved in front of them to simulate life—small “snake sausages” made from minced mouse meat and even bits of minced liver. Live foods are essential to an unstressed tarantula, but some keepers like to push the envelope a bit and try to adapt their pets to taking dead foods. Frankly, it seems best to me to stick to crickets, which will provide a tarantula with all its nutritional needs at little risk.
Feed a wild-collected tarantula as many crickets as it will eat for the first week or two and then taper off to just a few crickets as its body fills. Most keepers try to feed their pet two or three crickets a week once they are fully acclimated and eating regularly. Remove uneaten crickets within a day after they are offered. Crickets may decide to attack a sleeping tarantula, treating it as food and they could damage a small tarantula. Some hobbyists place a small dish of cricket food in the cage to avoid this risk. Crickets often will drown in an open water bowl, so make sure they have a way of walking out of the bowl.
Don’t feed insects that are too large for the tarantula. This is especially true for small and young tarantulas: the food should not be much longer than the spider’s body is wide. Large prey may cause the spider to work too hard to get its food, spending more energy in the battle than it gets from digesting the insect. This may be especially true with larger grasshoppers, giant mealworms, and such strange items as pinky mice. Even the largest tarantulas do quite well on many small insects at a feeding, so just watch your spider and adjust the size and number of prey to its feeding habits.
Tarantulas often go on short fasts (or up to several months for burrowers from temperate climates), especially a few weeks before molting or laying their eggs. These fasts seldom are harmful unless the spider fails to feed for more than three or four months. A fasting tarantula may or may not break its own fast. If the keeping conditions are already satisfactory, there is little you can do to make your spider eat.