I was doing my daily rounds watering and feeding the critters today and I discovered a new batch of baby crabs in a hank housing only a single female Geosesarma sp. Red Vampire Crab!
Sometime last summer I captured a female vampire crab who had just molted (slower and easy to catch at this time) and put her by herself in a tank with the plan of capturing a male in the main colony and putting him in with her. Well I never caught a male to go with her and yet today I saw about a dozen babies darting around. Now there is a SLIM possibility that she had been mated before I captured her, however two problems with that scenario arise:
1) Molting generally makes insects and creatures who molt "virgins" again so the males sperm packet should not still be with her.
2) Even if she had been mated their gestation/egg carrying period is only around 30 days, she has been alone since molting at least 6 months ago.
The only way I will know for sure is to segregate some babies and raise them to breeding age and see if the females who have never been near a male at maturity will still produce babies. Or simply segregate and raise these babies to maturity and see if they all turn out to be females.