Are you feeding him at an off hour? His internal clock could be confused after being taken from the wild into an indoor environment. Temps could be too low as well, or he could have a nutritional or other health issue. Most wild caught HLs end up being in poor shape by the time they are sold from what I have seen.

Put the ants in the fridge to hibernate them. Then put them a few at a time in the tank with him. As they begin to wake and stir he should get interested. A harvester ant moving about quickly in an enclosed space can spook a HL.
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"A man that should call everything by it's right name, would hardly pass the streets without being knocked down as a common enemy." The Complete Works of George Savile, First Marquess of Halifax 1912,246