1. Healthy competition is not alien even for such animals as snakes. For a place in the terrarium there can be a serious struggle that ends with violent fights and, accordingly, injuries and stress for both opponents.
2. As a rule, the larger snake in the terrarium becomes a leader, harassing others at the same time: she gets most of the food, the place under the lamp and drinking bowl, while the rest of the inhabitants of the terrarium, losing comfort, are subject to severe stress. Snake cann't tell you about it, but one day your pets under the stress refuse food and die.
3. You risk to find one rather than two pets in the terrarium if you ut there 2 snakes of different sizes.. Cannibalism isn't unusual among reptiles. Sometimes it is caused by competition, sometimes by density. Sometimes snakes (especially young) might accidentally eat each other, taking it as food. Often dies not only the victim, but also the "cannibal". A similar situation occurs while feeding both snakes rush to one place (so if you focus on the joint keeping of the reptiles, feed them in separate containers).
4. Snakes are subject to a variety of diseases. If reptiles have been quarantined, eat well and look healthy, any of them can be a carrier of the disease and pass it to relatives. As a result - all in the terrarium are ill (and well, if they don't die).
5. If there's a belch in the terrarium, then you probably will not be able to determine which of the snakes has done it and take appropriate actions.
6. Keeping in the terrarium couples of different sex snakes - the question is not less controversial. Male and female in the same way will be competing with each other, except for the breeding season. If your snakes are young, be aware that males puberty often occurs earlier than females puberty. The male will constantly annoy female, inviting her to coition, interfere her to eat and relax. Despite stress, this situation is fraught with early pairing and, as a consequence, the death of the female.
Of course, all written above isn't the ultimate truth. There are cases of joint content of boas, pythons, corn snakes and other species. Despite this, we strongly recommend not to jeopardize your snakes and buy each of them a separate terrarium (container).