Wetapunga are heavy, wingless and nocturnal. They shelter in vegetation by day, emerge at night to feed on leaves, and are preyed on by the birds and reptiles that occupied New Zealand's predator roles. Large gravid females have been weighed at over 30 grams, heavier than a house mouse, which is what gives the comparison its force.
The comparison should be held loosely. Weta are not warm-blooded, grow by moulting, breed once and take a year or more to mature, and their metabolism and behaviour differ from any rodent's. What the parallel captures is a functional point: on an island without terrestrial mammals, the ground-dwelling nocturnal browser niche was available, and insects filled it at a size that insects rarely reach elsewhere.
That body plan became a liability. Slow, flightless, ground-active and edible, wetapunga were removed from the mainland by rats within a short period, surviving only on Little Barrier Island. Conservation now consists of captive rearing and translocation to islands and fenced sanctuaries where mammalian predators have been eradicated.