Interesting fire power feat, a Mini Nuke can one shot/blow up the Gigapede
It blows it up so hard there it's body remains travel hundreds of yards
No exact measurements are given for the adult Gigapede but the Hatchlings of it are 3x the length of a horse (8 meters)
It's probably 16-24 meters, pretty impressive feat especially cause the Gigapede is super durable.
Edit: Just consistency with Mini Nukes being in the multi tons of TNT.
(The Abbey is a settlement built in and around a Church so it's like a large building lvling explosion)