I'm sorry to say so, but I suppose you are not very familiar with ants?
I can't be completely sure since you have no picture, but the way you describe it, very possibly these 2 larger ants were 'soldiers'.
Most ant colonies exist of 3 different types of ants. They are all sisters from each other, and daughters of 1 queen. A queen stays in the colony and her sole purpose is to lay eggs. She does this continuously (while she is fed by worker ants) and thus never leaves the nest. She stays there until she dies. The worker ants are 'workers', gathering food, expanding and repairing the nest when needed, taking care of the eggs and larvae. They are small and probably the type of ants you think of when someone is generally talking about ants.
The last class of ants are the 'soldiers'. Their task is to protect the colony agains intruders (an other ant colony, termites, other insects or animals,...). They differ in size from the worker ants (differences can be small or very big, depending on the ant species). Soldiers are bigger than the worker ants, and have bigger mandibles (used to "bite" intruders) and thus bigger 'cheek muscles' to operate these mandibles. Possibly this is what you described as the 'hunchback'.
Furthermore, ants use chemical signals to communicate with each other. They can lay a 'track' of these chemicals, for example, to show the way to a food source to other worker ants, which can then follow the track and help to bring the food back to the nest. Often the worker ants (gathering food) are accompanied by several soldier ants, to protect them from other insects (or animals,...). These soldier ants also use chemicals to communicate. When attacked, they can release an alarm chemical that attracts other (soldier) ants, to come help them fight an intruder.
Most possibly, by using the poison you killed some ants, which results in the automatic release of the 'alarm signals', attracting even more ants...
I hope this answers your question.