Ok, as most of your might have read in my logs here that I recently managed to get the twin ants on my Morino Tamagotch. Well I'm going to help other to get them too!
First off my method might not be 100% sure since I've only done it once so far but here goes nothing, start off by hatching the white egg (why I said this I have no clue why) and care for your babymotchi till it changes into imotchi. From here only feed it the second food option till it goes into the cocoon. Also don't let it beep for games, I only let mine drop to 1 full leaf for happiness and to make it gain weight faster only played 1 game at a time when this happened (predator attacks helped fill the rest of the empty leaves though).
You want to get your imotchi to 50mg before it reaches the age of 3 and goes into it's cocoon, at this point set the temp to the hot side and let it go all the way over before setting it to cold and letting it drop back to the middle. Once it drops back to the middle set it back on the hot side and TA-DA!
This is the exact method I used in getting FutagoAritchi and once my twin ants leave I will try it again to make sure it works every single time.