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So, let’s talk about egg sacs. This is a mature female Heteropoda boiei. A large species of huntsman from Malaysia. For scale, that’s a subadult locust which was almost 2” long. She has a leg span of somewhere around the 5-5.5” mark & she’s not the biggest I’ve seen.
They inhabit warm, humid forest environments, so in captivity they should be provided with a spacious arboreal enclosure, ideally with live plants. Plenty of vertically inclined bark slabs and branches should be provided. Here’s one newly set up which has since grown in well.
Many (most) of the specimens that become available are wild caught which is generally best avoided, but as the females are usually mature & therefore very likely gravid, they are a good way to get captive born offspring into circulation with which to begin captive breeding.
My current specimens are the offspring from my last (now deceased) female, and a wild caught female I got from a friend who was downsizing. This female is the one I’ve posted about recently who made a sac a few weeks back.
In the picture above, she had just appeared with this sac having only very recently made it. In order to make a sac, this species spins a thick, circular mat of silk, usually on a vertical surface, and then creates a pocket (by pulling up an edge) in which she lays her eggs.
Once the eggs are laid, she continues to cover them with silk whilst folding all of the edges of the mat inwards and sealing the whole thing closed with more silk. The result is a disc shaped packet of eggs. She then carries this until they’re ready to emerge.
When the eggs hatch, the spiderlings are very underdeveloped, being not much more than an egg with rudimentary legs. This first instar stage (below) will undergo its first moult within a few days of hatching, all whilst still inside the sac.
It is only when these spiderlings have had a chance to harden off post-moult that they emerge from the sac. At this stage, the sac has begun to look very swollen. The female will suspend it from silken threads & quite often will open the sac slightly herself to help them out.
Once the spiderlings have emerged, they will cluster together and stay in a group for the first few days to a week or so. They seek safety in numbers, but the clusters that they form serve a couple of other protective purposes too.
First of all, a cluster of baby spiders blends in very well to the undergrowth and does not look immediately like a meal to would be predators. Secondly, at the slightest vibration/perceived hint of danger, the spiders will scatter in every direction causing much confusion.
They will then reconvene later and will stay grouped until they are ready to disperse and begin hunting for themselves. In captivity, I have found that prey tends to be ignored for the first few days, but will be readily accepted right around dispersal time.
Having just emerged yesterday, I will offer these spiderlings prey for the first time in a couple days & then see about splitting them up individually in a week or two, depending on what sort of levels of cannibalism I begin to see.
Here’s the video of them scattered again. You can see the mum clearly, and how much bigger she is than her young. She will not be interested in eating anything that small, so she is unlikely to eat any of her babies before I move her back to her proper enclosure.
And finally, the baby ball video again, just because. See how they look much more like an old dried up seed head or something similar than a ball of delicious snacks? Smart 
So there it is. I’ll try and be better about documenting where it goes from here. And I suspect the female will lay at least one more sac given the size of this one, so I’ll do better with photo-documenting that too if she does 
