Actually, it wouldn't have worked even if it WAS a 3.5" floppy, because the old Apple floppy drives (even the pre-1.4MB Mac ones) used variable speed mechanisms, which no currently available drive can read, and no USB floppy drive has ever been able to read.
The situation with 5.25" drives in Apple machines was similar--they used some seriously funky hardware tricks that made the disks unreadable with a normal PC 5.25" drive. I ran into this recently because I actually managed to find a 5.25" drive and get it functioning in a Windows (XP!) box to extract data, but it won't read Apple disks.
However:
http://www.oldskool.org/disk2fdi
..this page claims to have a DOS-based driver that is able to read data off an Apple // disk. You can probably find an archaic DOS machine with a 5.25" drive at a junk shop somewhere, and if this software actually works you can then get data off the Apple disks and onto either a standard 3.5" disk, which can be read easily with any USB-based drive on a Mac, or onto a hard drive which you then extract data from one way or another.
There are three alternate methods:
1) Find an Apple // with a working 5.25" and 3.5" drive. Copy the 5.25" disks onto Apple 3.5" disks. THEN find an old Mac with a built-in 1.44MB 3.5" drive--these can read old variable speed Apple // disks (and in the case of newer ones, also write standard 1.44MB disks). From there, either put the data on a drive, a USB key if the Mac has a card, copy it to standard 1.44MB floppies and read those with a USB drive, or use some other means of extracting the data.
2) Find an LC with the Apple // personality card. My dad had one of these, and you should be able to plug an external 5.25" drive into the card, fire up Apple mode, and copy the data either onto the hard disk or some other useable format. I've never actually tried this, though if I had enough free time I would.
3) I've read tutorials on Apple // emulator sites on how to basically rig a serial connection between an Apple // and a Mac, and use a special piece of software on the Apple to feed data from the floppy drive onto the Mac. This looks hairy, to put it mildly, but might also be an option. Hunt down some Apple // emulator software if you're interested in this.
Incidentally, I just went through a similar thing trying to clean data off of nearly 1000 ancient 3.5" disks, which were a combination of old PC ones and REALLY old Mac ones that were only readable with one of the variable speed built-in drives in an old Mac. Took me weeks just to get a working Mac floppy drive, despite having piles of ancient Macs around. Those things are not durable, and PC drives are worse.