Generally the main role of the Bug Biter is to sneak damage in, either to fly between enemy units packing a mortar and / or rigged explosives or to get close to the enemy summoner to put assassination pressure on by threatening triggering the explosives with a mortar attack or with Detonate.
Also a great unit to Detonate as it costs 0, so you can play it, send it into enemy lines with the rigged explosives and a Turret Upgrade, do a bunch of damage, Detonate and get everything back leaving no magic for the opponent to make.