  We present a microscopic investigation of frequently observed
impurity-induced states in stoichiometric LiFeAs using low temperature scanning
tunneling microscopy and spectroscopy (STM/STS). Our data reveal seven distinct
well defined defects which are discernible in topographic measurements.
Depending on their local topographic symmetry, we are able to assign five
defect types to specific lattice sites at the Li, Fe and As positions. The most
prominent result is that two different defect types have a remarkably different
impact on the superconducting state. A specific and quite abundant Fe-defect
with $D_2$-symmetry generates significant impurity-induced additional states
primarily at positive bias voltage with pronounced peaks in the on-site local
density of states (LDOS) at about 4~mV and 12~mV. On the other hand, a
$D_4$-symmetric As-defect causes a significantly enhanced LDOS at both positive
and negative bias voltages. We expect that these findings provide fresh input
for further experimental and theoretical studies on elucidating the nature of
superconductivity in LiFeAs.
