I saw the mommy spider spin the egg sac on 21 August, and this morning, the 6th of September, they finally emerged. These are Parasteatoda tepidariorum — note the leopard pattern on the abdomen. That’ll turn into a more complex mottling as they get older. Also see how the legs are mostly pale, but with distinct bands.
Steatoda triangulosa has a longer incubation time of 30 days, and the spiderlings emerge with pale abdomens and black, hairy legs.
The important thing about this is that we can nail down how long the incubation period for both species is under our specific culturing conditions. Now we wait for the Steatoda borealis egg sac to hatch out so we know its incubation period. Then…comparative embryology!
By the way, the lab was hectic this morning, with 150 tiny baby spiders, each about 3/4 of a millimeter long, emerging all at once and immediately trying to disperse. There was a cloud of barely visible dots all radiating out instantly from the locus of their home vial, while I was frantically trying to gather up individuals and put them in separate containers. Some, I’m sure, escaped.
Hmmm, is it ever a good thing when a scientist says that?