Foreshadowing?

Nope. Just bugs put there to make the place look "icky." No foreshadowing whatsoever, especially considering they already named the monsters that will be in the sequels. And at the time of filming, they weren't sure if there would even be any sequels.

I think they hasequels plan. Whw would they waist the money they spent on Rodan and them

the sdcc teaser monster is just an early muto concept, i dougth it will ever be used

The Mothra name on the tank was just an easter-egg, Gareth said that we wasn't planning on making any sequels, but he would leave an open ending just in case they do ask him to make one. 

And just because they named Mothra Rodan and Ghidorah to be in future installments doesn't necessarily mean that they won't add some of their own created Kaiju into the mix, like the OP said, it might just be a minor monster setting up for the bigger ones.

^ As in it might be a monster that will appear just so that Godzilla can show his power by killing it easily.

RANDALLG95 - Welcome to SCIFIED! It is always quite nice toi see new faces! As for the hypothesis you have presented: that is a very interested idea! It may be that the little creatures presented in the first film were simply there to add atmosphere; however, anything is possible! It very well could be that we see a millipede-like monster in the upcoming film! Thank you ever so much for sharing your ideas with us, and, once again, welcome to SCIFIED! :)