Non-dependent on sunlight, UVA & UVB doesn't mean snakes can't benefit from some. . .
Corns have been observed to be *non-dependent* on full spectrum sunlight, UVA only or UVB only. But the fact that they don't absolutely need these light wavelengths for survival does not mean that they might not benefit from a little exposure.
Some lizards and turtles can't even survive without these wavelengths, developing the equivalent diseases of rickets [juvenile] or osteomalacia [adults] without the Vitamin D3 produced by such exposure. These animals don't get Vit D3 in their diet. Snakes have not been observed to develop these outright Vit D3 deficiency states without this light because of their consumption of whole mice.
However, mere survival of an animal is quite different from optimum health for that animal.
Here's what we know about the action of sunlight and its component wavelengths on amphibians and upwards through the phylogenetic tree, all the way to humans [if you consider humans to be at the top, LOL]:
[1] UVA light catalyzes the conversion of precursor chemicals in the skin, starting with 7-dehydrocholesterol which UVA makes into "previtamin D3", and then into Vit D3, the biologically active form of Vit D. Of course, if Vit D3 is in the diet in a whole organism like a mouse, deficiency without sunlight exposure is unlikely. [Doctors use prescription Vit D3 to treat certain metabolic and neoplastic diseases in humans when they are unable to make Vit D3 themselves.]
But. . .
[2] Visible light along with UVA and UVB inhibits the release of the hormone melatonin from the pineal gland. [Melatonin is sold over the counter as a sleep aid, and if you try it, get some low dose 2.5 mg sublingual tablets to start, as the normal swallowed form takes too long to work.] The varying length of daylight throughout the year is one of the factors which synchronizes animal reproductive behavior to the seasons, through this pineal gland and melatonin. Also, the dawn, day, dusk and night acting throughout a 24 hour period further synchronizes biorhythms, again through the pineal and melatonin.
[3] Through mechanisms in [2] and other as yet unknown mechanisms, sunlight can have profound effects on mood and behavior in ways more general than mating. Ever hear of Seasonal Affective Disorder in humans, otherwise known as the Wintertime Blues? It can sometimes be treated by inhibiting excess melatonin release, by exposing humans to bright full spectrum lights at a certain time for a few hours a day. Ever wonder why hibernation or brumation synchronizes to winter--the reasons involve BOTH temperature drops and dimmer sunlight for a shorter time each day.
[4] Also through [2], [3] and other as yet unknown mechanisms, visible light, UVA and UVB affect the production of growth hormone and other pituitary hormones, along with levels of thyroid hormone, cortisol and the sex hormones testosterone and estrogens [there are actually 3 different estrogens]. Essentially, all of these levels increase with sunlight, except for levels of cortisol which fall [unless there is a severe sunburn]. All of these hormones have *profound* effects on the physiology of all animals [endocrinology is the medical field that focuses on hormones and their effects, and is about 50% of my medical practice]. You may remember another post of mine that spoke of how physiological [bad temps, starvation] and psychological stress can elevate levels of cortisol, which can suppress an animals immune system leaving it susceptible to infections. Because sunlight exposure in moderation can lower cortisol levels and raise levels of the other beneficial hormones, it can contribute mightily to overall health and well being.
And that's just the beginning of what we know! Then there's what we don't know but suspect! So even if Vitamin D3 is completely provided from diet and supplements, there are a lot of other effects from sunlight that can't be easily duplicated without it.
My vet and reptile ethologist friend and I have had many discussions about this. Recognizing that snakes are nocturnal and tend to hide in the wild, it's clear that they don't need a lot of sunlight for optimum health, and in fact amelanistic or snow corns would be poorly adapted to a lot of sunlight [sort of like redhead or albino humans sunburning very easily]. But we do recommend holding your snakes in direct sunlight for about 5 to 10 minutes ONCE A WEEK, for optimum health. Late afternoon in the summer because the sunlight is so strong, 1-2PM in the winter, and adjust in between [I live in Dallas, adjust accordingly by common sense at much higher or lower latitudes]. Be very cautious and limit time to 3-5 minutes for the first few times, and then slowly increase to a full 5 to 10 minutes--it's just like building up gradually when tanning. ONCE A WEEK.
We also prefer having a tank exposed to natural sunlight in the day, even though the glass in the tank and windows will block nearly all UVA and UVB rays. But the visible light and the timing of sunrise, day length and sunset will still do their magic. If this can't be arranged because your snakes are in a windowless room, an adequate substitute can be had by using a plant grow light which is closer to full spectrum in wavelength components. This can be operated on a timer adjusted periodically to sync with sunrise and sunset. I know of one snake owner who has a remote photocell in a window to synchronize his lamps to actual sunrise and sunset, since his snakes are kept in his basement.
When I started doing all this, I noticed a dramatic increase in the physical activity and apparent "awareness" of my snakes within the first week. This was not a scientifically controlled experiment, but I think it's a reasonable and safe conclusion to draw. On X-rays the bony skeletons of my corns appear extremely dense compared to X-rays I've seen of other corns.
Recapping, it is correct that sunlight, UVA or UVB aren't *required* for your corns. But corns can benefit from many things that aren't required, but are still health promoting, just like humans and other animals can.
Get a tan AND get a life,
Doctor Mike
