Crickets, Gryllus sp., are the most common tarantula food. If you dont want to breed them you probably can find them in your local petshop or you can order from insect breeders.
Grasshoppers are high in nutritional value. Same goes for grasshoppers as for crickets – found in the petshop if you dont want to breed them. You can catch them on meadows along with similar insects during the summer months. Do not feed wildcaught insects if the area is treated with pesticides.
Left: Blaberus discoidales – Right: Blaptica dubia
Adult cockroaches are excellent food for the larger spiders and juvenile spiders eat smaller roaches. Many roaches are easy to breed and some dont climb on glass (such as Blaberus discoidales and Blaptica dubia) and the culture dont smell. Watch out for german cockroaches, Blatella germanica, they breed in apartments and are almost impossible to get rid of.
Zophobas morio is a beetle whose larvae is a common reptile and arachnid food. The larvae have a tendency to burrow so when I feed with these worms I crush the skulls with a forceps before I put it in the tarantula cage.
I feed spiderlings twice a week. It depends alot on the species, a Theraphosa spiderling require more food than a Aphonopelma spiderling. You can put a freshly dead larger cricket to you spiderling if you dont have small crickets. It will consume as much as possible and discard the rest. Dont be afraid to overfeed your spider – it will only eat as much as it wants. Give the spiders the food items one at the time, othervise the spider can get stressed and makes it difficult to supervise if the spider eat or not. Another problem with lots of crickets running loose in the spider cage is the female crickets are often gravid and lay the eggs in moist substrate. Also if the spider goes to molt and a cricket is loose it could seriously hurt the molting spider by eating on it.