Does anyone know what causes the spider cracks to develop, what can be done to prevent it, and/or is it something that can or should be fixed. Thanks.

Its normal unless it leaks then send it in to get fixed.

Not 100% sure what causes it but ive heard it happens with the liquid inside expands and contracts. I dont think it is preventable.

While I have no direct experience with ACOGs, my experience with parts made of what I believe to be similar materials suggest that hardening from age and sunlight, and then cracking due to vibration or shock once it's hardened could be the answer.  

If so then preventing it completely might be impossible, but delaying the inevitable may be possible with anti UV treatments and chemicals designed to keep the material from hardening.  While I highly doubt a good anti UV treatment like 303 (I use 303 on almost everything that gets prolonged sun exposure and have never seen it hurt any material and it really does work well) or a wax with UV protection built in would hurt the material it's made of, only Trijicon, or someone else with experience in that particular material, could tell us what chemicals would be safe and effective to prevent age hardening.

It doesn't cause any issues.

My understanding is that the cracks are a consequence of using a material with such a high level of light transmission.

what part is cracked?

CLICK HERE for a thread on the subject

Thanks for all the responses, insight and link to the previous thread. If mine develops a leak I'm sending it in. Seems to me the fuild in the tube is as important to light transmission as the material they make the tube (that cracks) from. I love my TA31F and I know this condition doesn't effect the performance, but those cracks really bug me..