The Tekseers seem to be created by an entire platoon, perhaps army, of A222 scout and recon infantry. Whatever happened remains unknown, but the distinct appearance is uncanny. What is certain is that they are no longer who they once were. Tekseers use sniper weapons not of their own and keep to long distance, and are generally slow. Tekseers, however, are woefully outmatched at close range, and getting up close will assuredly send them into a panic. While they may not attack while panicked, they certainly will pick up the pace. Hitting them at close range, especially with melee, is a triumph all its own. It's wiser to use their fear of close range as a method to keep them from attacking rather than to get an advantage outright.