The bridge originally opened on April 4th, 1910, built only as wide as the main arches underneath. When cars came along (first model T built-in 1912)... The bridge was only wide enough for two lanes. The bridge was expanded from two to six lanes in 1980 The expansion joints underneath the newly expanded bridge proved to be a perfect habitat for bats… this was unintentional. Bats were not initially welcome to the bridge, locals were afraid of disease and getting bit. (Local Headlines read “BATS INVADE AUSTIN” & “DON'T LET YOUR CHILDREN PLAY BY THE CONGRESS BRIDGE AFTER DARK” Locals took it unto themselves to rid the area of its new furry inhabitants by shooting them with shotguns apon there nightly emergence & pouring acid into the cracks atop the bridge. Bat Conservation International caught wind of the bat eradication efforts and moved there international headquarters to Austin to help conserve and protect the unique bat population. Mexican free-tailed bats are very important for keeping crop pests in check as they can eat up to two-thirds of their body weight in insects each night, especially while lactating and feeding young. With the large numbers of agricultural pests they eat, research has demonstrated that these bats can save farmers up to two applications of pesticides per year. They can eat their body weight in bigs nightly, that would be like one of us eating 25 pizzas in one night… When the first cold fronts start pushing through the Texas Hill Country in late October to mid-November, the Mexican free-tailed bats begin their migration back to Mexico. In 1995, the Texas State Legislature named the Mexican free-tailed bat as the "state flying mammal."