The complete life cycle of House Crickets is approximately 8 to 10 weeks. Your decision of the correct cricket size to buy depends upon how you plan to use them. For fishing, buy adult crickets. If you plan to feed live crickets to your pets, care must be given to not feeding crickets that are too large for them. A common rule-of-thumb for smaller lizards is to feed crickets that are no more than 1/3 the width of their head. For finches and other small birds, buy pinhead crickets or 1/8 to 1/4 inch crickets.