How did you go about checking your temps? I use an IR pyrometer with a 95 Emissivity setting and find that unless the pile is HOT (above say 120F) there are going to be temperature differentials all throughout the pile (and these can be rather large temperature swings from one location to the next). Some places as little as a cubic foot will show fluctuating temperature from adjacent areas and even within that volume the temperature will still vary measureably. The larger the pile mass and the warmer the pile, the larger any area of consistent readings will be, probably due in part to the insulating factors. Just like your yard is full of micro-climates, so too is your compost pile. You need to be able to take instant, small area temperature readings in order to accurately assess what your worms are experiencing. IR pyrometers can now be had for under $17 and will give you that ability to instantly (literally at the speed of light) measure the temp of an area about an inch in diameter. It really needs to be an instant reading because the moment you open up a compost pile the outside atmosphere begins to affect the internal temperatures.... old-fashion thermocouple based pyrometers can take a minute and often quite a bit longer to get up to temp and by then it's changed. Burying the tip of the thermocouple is not a solution either because doesn't allow you to see exactly where the temperature is being taken from and you will miss all the micro-climate changes within the pile. I've measure temp (with and IR) with my own compost piles and (depending upon a number of factors) have seen differences of more than 30 degrees within several inches (under a foot), of course this is temperature deep within colder piles.... as stated previously, larger and warmer piles tend to give more consistent readings over a larger area (actually its volume).

A few weeks ago I split up my worms (that were located in the warm basement) and started two new bins which I put in the much cooler garage. Though they slowed down a little, they are still healthy and converting scraps into gold, albeit slower than the guys in the basement bins. I find that they tend to congregate in the warmer parts of the bins... these are where the often "greener" and higher nitrogen scraps are actively decomposing, however there are always some in every location in the bins.... I can't say for sure how active they are but all look fat and healthy so yeah, I'm not really surprised that your worms are fat and happy in the 40Fs, I'll bet they are a little slower moving though.

They could also be there just because, temperature notwithstanding, the compost pile is more hospitable than surrounding spots. It doesn't necessarily mean that they wouldn't prefer it warmer--just that they're perfectly capable of making do with what they have.

My guess is the worms were at the warmest part of the pile. Keep in mind this is a cold pile from last year.

I do have an IR thermometer but wouldn't use that unless I was looking for surface temp. I have a 30" compost thermometer but would only use that on an active HOT pile.

What I used was a 6in. digital kitchen thermometer that I have used for many years now to check the soil temp in the garden which was also 46.

6in. down gives me a good idea when I can start planting seedlings out.

fwiw - the ambient air temp was 64 at the time of measurement.

I find red worms in piles and random places in the yard all the time, including when well below 'room temperature'. They live through frozen winters (albeit dormant) just fine outdoors. In short, they are much hardier than most think.

that said, an indoor bin is a different set of challenges and they won't be as productive (shouldn't that be consumptive?) in an outdoor pile year round as an indoor bin might achieve.