Screenshot with abilities showing: It has a special ability called Qiraji Fortitude. The buff in my spellbook says it increases party/raid member stamina by 153. But the buff I actually receive is sta + 403. (EDIT: this was later removed and beetles made tenacity and will have their own family ability)
EDIT: Also, out of interest, the Hazzali workers (that spidery type of silithid) are also now listed as beasts (I don't think they used to be) and have diets, but are untameable.
UPDATE: I'll add colours as I go:
Purple one, Centipaar Tunneler (SilithidScarabSkinPurple): Temple Scarabs in Uldum are tameable, but (i) they're too high level for me yet and (ii) they freaking burrow and disappear often and stay underground for ages, so it's hard to get a decent screenshot of them. They have at least several different skins. I noticed four colours, three of which match the skins that Wowhead lists for the new "UldumScarabSkin" types, namely:
(i) UldumScarabSkinBlue, (ii) UldumScarabSkinPurple (iii) UldumScarabSkinRed (actually green with red back spots) (iv) SilithidScarabSkinRed (shiny red with teal markings, which is an older skin). However Wowhead lists a 4th new Uldum skin I didn't see: UldumScarabSkinTeal, but it could well be out there. WowModelViewer reveals a 5th Uldum skin, UldumScarabSkinYellow, which hasn't been mentioned on Wowhead at all.
Here is a screenshot of the "Blue" one being beast lored: And a distant pic of the purple one: LATER UPDATE: The tan beetle (SilithidScarabSkinTan) was added back to the silithid hive in the Thousand Needles and renamed the Silithid Defender, as detailed in this thread:
http://forums.wow-petopia.com/viewtopic.php?f=28&t=4645
NOT tameable because not yet set as beasts:
- Gorishi Tunnelers (yellow, Un'Goro)
- Hive'Regal Burrower (purple, Silithus)
- Hive'Zora Tunneler (yellow, Silithus)
- Hive'Ashi Worker (blue, Silithus)
- Scarab in ZF
- Probably 1000 other beetles around the game, so I'm gonna stop listing. Try using this list as a guide if you'd like to investigate some more.
UPDATE: Skins that we haven't seen as tameable yet (7):
- SilithidScarabSkinBlack: (steel grey with tan markings) Qiraji Scarab
- SilithidScarabSkinGold: (copper with blue markings) Gold Beetle
- SilithidScarabSkinTan: (tan with brown markings) Silithid Searcher from Thousand Needles (possibly extinct)
- SilithidScarabSkinWhite: (white with black markings) Spitting Scarab
- SilithidScarabSkinYellow: (gold with blue markings) Gorishi Tunneler
- SilithidScarabSkinGreen: (green with purple markings). Not seen in game, but found on wowmodelviewer
- UldumScarabSkinTeal: (blue/teal with green spots) Turquoise Scarab (new skin in Cataclysm)
- UldumScarabSkinGreen: (ochre/purple with green spots) Venomous Skitterer (new skin in Cataclysm)
- UldumScarabSkinYellow (only found on WowModelViewer)
If you see any, please report in

EDIT: just found UldumScarabSkinGreen on cata.wowhead. Anyone seen this beast or this skin?