I would like to point out that the main balance issue with the wood ant melee soldier is not that it's weak compared to other species, but that it's not very effective compared to wood ant workers. Melee wood ants need an edge to ensure that they are the most viable tank within their own nests, rather than being overshadowed by a non-combatant unit that happens to serve its role just as well.
The main advantage that wood ant melees have right now is their high tolerance to AoE, since they can eat moderate AoE attacks without dying while workers tend to get obliterated immediately. This is worth considering, but I'm inclined to think it's such a minor edge that it can't justify their use in the majority of cases. That said, the melee soldier needs only a mild buff for odds to be tipped in its favor. Since it's a better option for AoE, it only needs to be just as efficient against most other opponents. This would give it a clear combat advantage, while the workers would remain a viable option preferred mainly for numbers (helpful for tasks like harvesting, but not for combat anymore).