It is unknown how long they have existed. Some sightings date back to 2017. But in the year 2031 Humankind was replaced as the dominant species on Earth.

They are known only as The Blue. Many believed that the Blue were created by a rogue nation as a weapon of mass destruction. But it soon became all too evident that this was not the case. These monstrous insect-like creatures now exert their terrible will upon the planet. As a result, the remains of the human race have fled into outer space to escape the infestation of the Blue.

Suddenly awakened after 22 years in suspended animation, Yuji Kaido finds himself thrust into a nightmarish reality. Yuji soon learns that the very survival of the entire human race rests in his hands.

Quotes:

“Blue Gender is best described as an addiction, one that is candy-coated with excellent character development and brushed with the venomous tang of suspense. ” --Play Magazine

"Blue Gender in both aspects are very much Western oriented in their style and emphasis on "Aliens"-like action sequences with a military bent to them and it's a strong aspect that's played out well. It's been good to be able to revisit this property since it has been quite awhile but in the end it's made me want to haul the box set out and watch that all over again." - ANIME ON DVD