- Hi There! We have some recently hatched baby white tails in our house - (noticed them yesterday, on the ceiling, about 15 or so... & counting! - I'm thinking they hatched in the roof & have come inside via the downlights) I'm just wondering how many are usually produced from one egg sac, is Summer traditional breeding/baby spider time, and how long do these little guys take until they become BIG guys?! thankyou so much! Kathy.