It is always nighttime in a dark wormbin. I suspect it is more temperature related.

I tend to agree with mendopete, BUT... I'm not entirely prepared to discount an 'internal clock'. While diurnal cycles are mutable, they have very strong genetic foundations.

If one would question the 'sensor' (as I do with the photophobic nature of worms), one must acknowledge that worm do in fact 'recoil' from light when no photoreceptor is known.

mendopete's explanation is the most parsimonious one, and I'm a very strong acolyte of Occam's Razor which states that among competing hypotheses, the one with the fewest assumptions is most likely the correct one.

Is your garage heated? If not, it is likely that by 2300 (11PM) the heat from the day has subsided sufficiently that the worms are willing to come out of the moist, cool bedding, to the surface which, in the heat of the day has "hot", dry air and now at 2300, has moist, cool air.

Paul

No, the garage is not heated. The bin is covered with the lid most of the times, so I would think its always dark inside. Still the observation was they like to come out during late night time.

Temperature and internal clock theories make sense. I am more inclined to think its internal clock that might be related to temperature as their relatives in wild get active mostly during night time. So a temperature drop during night or internal clock kicks in which sends signal to look for food.

They might be able to "feel" gravity or electomagnetic force from the sun to know if it's night-time or day-time. Maybe from the Earth's magnetic field, sorta like how birds navigate during migration or something.

I agree with the above re. light and temp. Is there a difference in atmospheric pressure between day and night (even w/o rain forecast)?

One must have a gravity "sensor" to sense gravitational pull. (In mammals and birds, the inner ear. In fish, the otoliths (ear stones)). The same is true for sensing a magnetic field. Since I am not a worm biologist, I cannot say with certainty that worms don't have gravitational or magnetic sensors. BUT...

1) I know of none reported, and
2) In the case of magnetism, since worms do not migrate geographically, why would a worm "need" that sense? Diurnal activity is MUCH more effected by light than gravitation. Gravitation, with respect to diurnal timing, is greatly confounded by the orientation of not just one, but three celestial bodies (sun, moon, and earth). "Light" is light, "dark" is dark.

I submit, with some caution, that they don't 'need' a gravitational senor either. Since they cannot fly into the air (unless they buy airplane tickets - a sarcastic postulation in another thread to explain worm travel from a lower bin to the one above it across the "air gap"), following their "nose" is sufficient for their behavioral needs.

Succinctly: It's not something I would argue about, but I don't think gravity or magnetism have any influence on worm diurnal activity.

I've been wrong before.

Paul