On adult females the only red is on the hourglass. They have those red dots while they are maturing.

This is a very good article but it still presents somewhat conflicting information about the identification of L. mactans.

The article says:
"The adult female black widow spider has a glossy jet black color all over, including body and legs. The only red marks are the bright red hourglass mark on the underside of the abdomen, and a red spot just behind and above the spinnerets."

But this diagram shows read marks on the dorsal side of the abdomen. I have seen some pictures where these marks are very distinctive. Do the marks disappear as the spider ages? Is this just a variation between individuals? Does L. mactans almost always have at least one read dot above the spinnerets?

that the male is a bit smaller. I was amazed how small he was when I found one the other day. I thought it must be an immature male, but was ID's as mature.