First, the important stuff. Rather than Curious George, the shovel that spends the rest of her life as a power plant is found in Virginia Lee Burton’s Mike Mulligan and His Steam Shovel, first published in 1939. Interestingly, a major plot point in that book was that Mike and Mary Ann (his shovel) could not find work because the steam shovels had already been rendered obsolete by the introduction of gasoline shovels, electric shovels, and diesel shovels. Yet, here we are, 65 years later with the “steam” descriptor persisting in the language. (Of course, that may be due to Ms. Burton’s work, itself, since the overwhelming majority of U.S. kids have that book read to them some time in their pre-school days.)
The term I have encountered for these devices has nearly universally been hoe, (track hoe, rubber wheel hoe, etc.). This is probably due to the nature of the digging action. In the Mike Mulligan story, the bucket was pushed into the ground by a winch pulling on the top of a lever that caused the bucket to dig away from the machine, much as a shovel or spade is pushed away from the digger. Modern devices use hydraulics to pull the bucket toward the machine in a hoe-like action. (Many of the machines have a coupling that allows the operator to drop the bucket, use the end of the digging arm to spin it around, then reconnect it facing away from the machine to be used with a shovel motion instead of a hoe motion–all without getting out of his seat–but the common digging motion is hoe-like.)
The Caterpillar site called all their digging equipment excavators, but in the field, I have generally found only the ditch grading equipment called excavators. They tend to have a digging arm that is pivoted at a single point, extending or retracting with a telescoping motion, with a bucket that is able to rotate at the end of the arm. Gradall makes a lot of them. The hoes generally have a jointed arm, pivoting at the cab (or “shoulder”), at the “elbow” and at the “wrist” that provides a lot of flexibility in directing the bucket to dig down or scrape a straight line at the bottom of the pit.
I am pretty sure that some of my terminology will be “wrong” in different parts of the country. One device with multiple names is the machine I grew up calling a fork-lift truck, that was called a high-low when I went to work in a shop, and was called (for no discernible reason) a towmotor at a plant where they were built in Mentor, OH.
A backhoe is simply a hoe mounted on the back of a general purpose tractor, where the mount allows the hoe to be turned while the tractor remains still, unlike the general hoe where the entire cab rotates with the bucket arm.
A loader is the wide-bucket device used for scraping dirt up or for digging into existing piles of dirt to move them from one place to another. They can be mounted on articulated (bend-in-the-middle) four wheel machines, rear-steering-wheel machines, or tracked bulldozer-like chassis. If they are mounted on the front of a general purpose tractor, they are called front-end loaders.
A tractor with a front-end loader and a backhoe is called a monkey, for reasons I have not yet discovered.
Rollers tend to be presumed to be diesel, these days, although there are a few gasoline powered rollers in use. Since they now have many variations of specific function, they tend to be known by their other features: three-wheel vs two-wheel vs single wheel with rubber tire propulsion. Vibrating tamping wheels, compaction wheels (with big cleats), mutiple rubber wheels, or other features.