>Day length and or temperature would seem a better bet, they certainly 
work in stimulating other cycles.  But others have pointed out that it 
is hard to see how this can operate in a dungeon.

What about some of the solitary mining bees, e.g. Andrena fulva.  These dig
nest tunnels as deep as a metre, yet the new bees emerge each year just as
the gooseberries and plums come into flower; they are synchronised with the
flowering regardless of whether the season is early or late.

At that depth, the temperature is pretty constant and there is no light so
what triggers their emergence at precisely the right time?

Best wishes

Peter
52°14'44.44"N, 1°50'35"W

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