Red Octane (the publisher of Guitar Hero) has sued the Ant Commandos for selling wireless guitar controllers for use with the game. Red Octane claims Ant Commandos copied Guitar Hero packaging and advertising materials, in violation of Red Octane's copyrights and trade-marks. They also claim false advertising with respect to Ant Commandos' claims that the guitar controllers work properly with the PS2.
Interestingly, Red Octane is facing IP lawsuits for its own activities. Konami claims that Red Octane's dance game Groove violates Konami's patents relating to Dance Dance Revolution, and KnuckleBonz claims Red Octane's use of GUITAR HERO violates KnuckleBonz's trade-mark rights in that name.
Coverage of the marching ants is here http://www.shorl.com/fadredrufrarine (Gamespot)