Eringi

Eringi are Mushroom-like creatures that travel in groups in search of food. This food is usually in the form of thermally unstable materials, ranging from small devices such as radios and bullets to objects such as nuclear warheads, as shown in episode 12. It is hinted that the Eringi may be an artificial species that was created to neutralize unstable energy sources such as weapons by consuming them. The most notable creature that would be classified as an Eringi is Nuko, who is met by Chito and Yuuri in episode 10. The name "Eringi" comes from a type of mushroom. It is shown that Eringi can "float" by unknown means.
Their existence was hinted at by multiple stone Statues of them existing in some neighborhoods of the City, including a temple complex. It's unknown who built these statues and why.

(Source: Girls' Last Tour Wiki)