Corpsers actually come in two varieties. While their appearence is largely the same, the tactics for fighting against them and their own capabilities are very different because of the sheer difference in size.
The smaller corpers (likely young) are quick and powerful. They have significant shielding on their front legs that prevent almost all damage from the front and can use their legs in powerful smash attacks. They can also use these legs to dig through dirt and rock to burrow under ground and surface in other locations. This makes them a tricky enemy to track and flank. Unfortunately, flanking is almost necessary to defeat these enemies because of their thick front armor.
Larger corpsers share most of the qualities of their smaller counter parts but their sheer size makes them difficult to deal with. They are usually as large as even the largest land vehicles (or larger) and are capable of extensive tunneling. Usually, they are used to dig tunnels to allow other Horde infantry troops access to an area. While they've only been seen tunneling through a wall horizontally, it is possible that they are also responsible for creating Emergence Holes in the ground. While it's not a common practice for them to destroy defenses from underneath, they are capable of causing at least minor seismic activity due to their digging.
Large Corpsers are usually not seen outside of vehicular combat though there have been instances where they have fought, particularly in tunnels. Since they are responsible for creating a large number of the tunnels, they usually can fill most of the tunnel, making it nearly impossible to pass until it's been killed. While it is possible to damage a Corpser extensively with small arms, it takes a large amount of ammunition and may still not kill them. During at least one instance, it was required to blow out a bridge to drop a corpser in liquid immulsion (similar to magma except it is also used as a source of fuel on sera) to kill it.
