  We constrain the cosmological density of cosmic string loops using two
observational signatures -- gravitational microlensing and the Kaiser-Stebbins
effect. Photometry from RXTE and CoRoT space missions and pulsar timing from
Parkes Pulsar Timing Array, Arecibo and Green Bank radio telescopes allow us to
probe cosmic strings in a wide range of tensions
$G\mu/c^2=10^{-16}\div10^{-10}$. We find that pulsar timing data provide the
most stringent constraints on the abundance of light strings at the level
$\Omega_s \sim 10^{-3}$. Future observational facilities such as the Square
Kilometer Array will allow one to improve these constraints by orders of
magnitude.
