Spade hackles are the fairly short and wide hackles found on the side of a hackle neck. They have long hackle barbs and the hackle bargs are stripped off and used for dry fly tails because of how long the barbs are.
Spey hackle is entirely different and come from many different birds and feathers. In short, spey hackle has very webby, long hackle barbs so the hackle reaches beyond the hook bend when palmered (wrapped) on the fly. It is typically wrapped from the second or thirds turn of tinsel from the tail and many times has 2 or 3 extra wraps made right in front of the body. Spey hackle is then pulled (stroked) down to the bottom of the hook so there are virtually no hackle barbs above the hook.
Spey hackle (or spey feather as it is often referred to in books or patterns recipes) can be blue-eared pheasant (the best heron substitute), white-eared pheasant (easy to dye any color), brown-eared pheasant, Chinese pheasant (the common ring-neck rump is the feather from this bird) feathers. Other spey feathers are coche (the side tail feathers of a rooster, usually sold strung), schlappen (the long, webby feathers at the top sides of a saddle patch, usually purchased strung), Whiting Spey Hackle (offered in necks, hen necks, saddles, hen saddles-an excellent spey feather), burnt goose (many time sold as spey hackle, a poor choice due to the thickness of the stem), or rhea (useful on the largest spey and dee flies, but can be hard to find). There is some very good peacock on the market that is useful for the largest spey and dee flies and you could also use pheasant tails if you split the stems and use only one side of the tail for the hackle.
I've seen some shops or shop employee selling strung spade hackle or strung extra large neck hackle as "spey hackle" or recommending it for tying spey or dee flies, but is isn't good spey hackle. I can't say this strongly enough: avoid using spade hackle on spey and dee flies! The barbs don't have the web needed and the stems can be brittle, as well as usually being too thick.
The easiest to find, most common spey feather is schlappen. It is cheap, comes in nearly any color you would ever need, and makes a very good spey hackle. The most expensive legal in the US spey feathers are the blue-eared, white-eared, and brown-eared pheasants; but blue-eared is the best substitute for heron currently available legally in the US. The Whiting Spey Hackle is an excellent spey feather, comes in a variety of useful colors (dyed and natural), is reasonably priced (top grade rooster neck is $30.00-$35.00), has a nice, flexible and small diameter stem, and very good barb length and count.
Hope this helps, even though I provided more info than you asked for.
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