Melburnians complaining about swarms of mosquitoes this spring need to take a good hard look at themselves. Or more specifically, at their back gardens.

Results of a CSIRO survey of almost 500 backyard rainwater tanks across Melbourne has found one in five were infested with mosquitoes - much higher than anticipated.

A DIY rainwater storage unit discovered in a Melbourne backyard. It also stores mosquito larvae. Credit:CSIRO

The biggest culprit was unmeshed overflows. Of the mosquito-infested systems identified, 60 per cent were without mesh, allowing mosquitoes to use the stagnant water as a breeding ground.

The survey conducted between February 2014 and August 2014 pre-dates the current boom in mosquito and other insects, due to a wet spring.