When Do Jack Russell Terriers Go Into Heat?

First season is usually around 5 to 7 months. After that about the same, about every six months or so. Yes they usually bleed when in heat. There is also the nerve wracking experience of trying to keep them away from all other dogs. They are more likely to fight (any dog but we're talking jack here as well) and should be kept away from intact males (if there is one in the house they can both drive you up a wall and even cause damage trying to get to the female on the males part), no public places or walks or anything and shouldn't even be in their own fenced back yard alone as those males can be crafty and can and have made it over fences. This is until 7 to 10 days after the bleeding stops and the swelling goes down (they are often very receptive when the unaware thinks they aren't anymore).
You can avoid all this and other problems by having your pup spayed. No more seasons, no more bleeding, no more crazy males ect. In addition to all that nerve wracking stuff there are many health issues that eventually occur when they are entire (as in many human females). An unspayed female has approximately 40 to 50 percent the life span of an unspayed female as a direct result of not being spayed and breeding. Even Breeders retire and spay after a few litters. Most females at some point end up having to be spayed due to some health issue that has arisen so it is safer and a better result to do so earlier when surgery may be less of a risk and all the hormones haven't already caused major issues (mammary cancer, uterine infection ect.) and things.
www.therealjackrussell.com  - breed parent club
www.irvinevetservices.com  - basic spay information
www.bullmastiffsonline.com  - detailed information on a couple of things that can occur in unspayed females
www.learntobreed.com  
www.dogfoodanalysis.com

Probably quite soon - maturity is around 6 months with Jack Russells, and then she should be on heat every 6 months or so unless she is spayed. You might find it useful to look at the Jack Russell Club of America if you haven't already - a very big, informative site.

Jack Russell can get their first heat cycle at the average age of 6-9 months. There can be 2 heat cycles in a year 6-7 months apart. Vaginal bleeding is one of the feature events of the heat periods in dogs. This bleeding occurs during first stage of heat periods and can last for 7-10 days. When this bleeding is reduced or ceased then mating takes place . So, bleeding occurs when dogs come in to heat.

Can a jack bleed whilst pregnant

Check to see if she has any problems with her heat cycle... Its only one doctor visit...