There are probably versions of these ideas already out there, but I have never seen them. The spark of this concept was The Apparatus Of Kwalish from 1st ed AD&D.

In my setting an elven wizard set about creating vehicles using the carcases of giant insects as a base. However, these are not undead giant insects, but constructs which are not autonomous. They require a driver to control them and are animated by magic.

Dragonfly

This two-seat helicopter is capable of high speed flight and is also extremely nimble for its size. It can hover, its claws can rake or grasp, and it is capable of lifting up to 500 pounds total weight, including pilot, passengers, and items both inside the 'head', (cockpit,) or grasped in the dragonfly's claws.

The mouth of the dead insect has been converted into a hatch which allows access to the cockpit, which is located behind the multi-faceted eyes. Each hexagonal panel in the compound eye focuses its view on the person seated behind the eye, with some panels giving detailed long range telescopic views, while others provide wide angle views in various directions. The pilot and passenger each have a full 120 degree view both horizontally and vertically, which overlaps to generate a 120 degree view vertically, from straight down to above and behind the seated person, and 200 degrees horizontally with the view to the rear blocked by the body of the dragonfly.

The pilot position is located behind the left eye, and has two controls. On the right side of the pilot seat is a lever which controls the speed of the wings by pushing forward to increase or pulling back to slow the wingbeat. A second larger lever on the left side of the pilot's seat controls the direction and flex of the tail, which allows steering while in flight from reverse, to hover, to forward, and allows turns to either side.

Between the pilot and passenger seat is a central console upon which are mounted six articulated levers which control the legs. When all of the levers are locked back into the reversed position the legs are retracted against the body to reduce drag. When all of the levers are locked forward into the forward position the legs are deployed in walking mode, and speed and direction are controlled by the pilot. When the levers are all or individually in the central neutral position the legs can be manipulated to strike or to grasp.

A successful strike can inflict 1d6 damage per leg which hits, while a grasp inflicts no damage, but grapples as if a huge creature with 30 Str were making the attack. If a grasp is intended to lift an object or being, each leg that successfully grasps the target adds 5 Str for the purposes of determining how much weight can be lifted. (For example, if three legs grasp for a total 15 Str, then an object or creature of up to 200 pounds can be lifted off the ground, treated as a heavy load for purposes of maneuverability.)

A grasp can also allow the Dragonfly to 'perch' on an otherwise unstable structure such as a rooftop or tree. Of course, the perch must be capable of holding the 300 pound Dragonfly plus its load, including the pilot, passenger, and their gear, while the legs must be free to maintain the grasp. While all six legs are required to make the initial grasp in this case, once perched the forward two can be released for other activities, such as cleaning the exterior of the eyes or manipulating something.

A Pilot feat is required to operate this vehicle without penalties. Without this feat any operations receive a -10 to any checks. This includes attacks, grasps, or maneuvers, but does not include savings throws. To qualify for the Pilot feat one must have access to such a vehicle or to a pilot with the feat who is willing to train him.


Beetle

Up to eight persons can occupy this vehicle, which is capable of rapid overland travel or limited underwater travel. While its exterior is not suited to carrying anything, its interior can hold a virtually unlimited weight of items, but there is a limited volume of eight cubic yards, (or meters.) Each rider and his carried equipment uses up one cubic meter. Encumbered riders use up one and a half cubic yards, (or meters.) For purposes of interior dimensions, assume 4.5 feet width by 4.5 feet height by 10.5 feet length. (8 persons is cramped accommodations!) access to the interior is accomplished via a 2 foot, (.6m) round hatch in the belly in the center between the first and second pair of legs. The driver can lock or unlock this hatch from his control position. It cannot be locked or unlocked from outside the vehicle.

The driver sits in the head of the Beetle and controls speed and direction of travel with a joystick type lever. It can move forward, back, or turn in place. He also controls the mandibles which can crush for 1d8 damage or grapple as a huge opponent with a Str of 40. A successful grapple allows automatic damage for 1d8 damage for each round so held after the first. The mandibles can either lift an object or creature weighing 1 ton, or push an object weighing up to 4 tons, (assuming an object with a flat bottom; heavier round or spherical objects can be moved.)

The driver also controls the first pair of wings which form two half-carapaces over the passenger section of the vehicle. The flight wings have been removed, (serving no purpose since a laden beetle would be too heavy for flight anyway,) and six crossbow/arrow slits have been cut into the sides, allowing archers to use crossbows or shortbows to fire through these slits. Slings, thrown weapons, or longbows are not useful due to space restrictions.

While the wings are up, entering water will allow the interior of the Beetle to flood. However, with the wings in the down position the vehicle can travel under water at 1/5 overland movement speed. It has no capacity to generate or refresh air while submerged, and there are only 8 man-hours worth of air inside the vehicle. Thus one person could remain submerged for eight hours, while four would be limited to two hours of underwater travel and eight riders would be limited to one hour of underwater travel. the Beetle always travels by walking along the bottom of the body of water, it has no capability to swim or even float.

The Beetle can also burrow in sand or fine sediments at 1/10 overland movement speed, but may not burrow through stony soil or rocks. Tree roots will also inhibit travel, and when burrowing the same rules for the air supply are used as for underwater travel.

Variations on a theme

Giant Ants
High speed single passenger vehicles

Giant Scorpions
Powerful combat vehicles with one or two controllers

Giant Crabs
Underwater combat vehicles with limited amphibious capabilities