The "Pre-ovulation Swell" is a phenomena I first noticed about fifteen years ago. This characteristic is normally observable as the female Boa begins to develop larger egg follicles. This is a prelude to ovulation. Egg follicles are typically present but in a size so small as to not be obvious in any way externally. As those egg follicles develop and enlarge, they create a thickening in the vicinity of the ovaries. This area is centered at a point approximately 2/3 rds of the way down the female Boas length. The "Pre-ovulation Swell" can be seen and identified, by the careful observer, if the enlargement from the normal size and shape of the female is noticed. It is most obvious just shortly before the first actual ovulation. In most cases the female will not get to this thickened state without the stimulation of male courtship. At least that has been my personal observation. I have seen some females show this thickening without courtship but not very often.
Lots of actual breeding will normally occur when the female is in the "Pre-ovulation Swell" condition. She is not gravid at this point as no fertilization has yet occurred.
Click here to view a video illustrating the Pre-ovulation swell:
The "Pre-ovulation Swell" is caused by the enlarging of the egg follicles. The enlargement appears soft or flaccid in comparison to the normal linier tightness one might see in a female Boa. The striations caused by the muscularity of the Boa running laterally normally create a distinctly different looking body shape compared to the body condition when the egg follicles are very nearly ready for ovulation. I think the mass of the egg follicles causes the female to appear larger. However, the female is noticeably more relaxed looking in this vicinity for some reason. Perhaps the development of the egg follicles requires that the females muscles surrounding the area of the ovaries be more relaxed than they normally might be. I don't know of a specific reason why this would be required. I just have observed that this softer appearance is there. Here is a female in the "Pre-ovulation Swell".
Above are pictures of a female Monster Tail Hypo that is very thick in the latter stages of the "Pre-ovulation Swell". Note how her body up toward the front on the left is quite tight, while the area right behind that tightness more toward the front of the image, is actually very rounded and soft looking. She is actually very squishy right now. If I gently touch her, I can feel how mushy she is due to the relaxed status of the muscles in the area where the egg follicles are located. The male Motley is doing his duty breeding her all he can to make as many of her babies as he possibly can.
I am pretty sure this little fellow was actually copulating when I took these pictures:
I suspect this female will ovulate soon. Likely within the next two weeks. Most of the time the female will darken noticeably just before ovulating. She has already turned quite dark and her mass is gigantic. I am hoping for a better litter than we had last time from her with quite a pile of little munchkins to enjoy!
This same female ovulated on January 22, of 2005 after breeding with a Jungle Boa. Here are a few pictures of her ovulating at that time:
Here is one of the babies she had in that litter:
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