It resembles some sort of pirate bug (see http://insects.tamu.edu/fieldguide/aimg50.html) except for the color pattern, but that could be variable. They are predatory on other insects. Normally a good thing to find (except in this case, of course). I don't think you want to get rid of it.
Assassin Bug. One of the best friends you'll ever have in your garden...I do NOT recommend you kill it...
The juvenile nymphs look almost like Stinkbug nymphs. The telltale tail is how you know which is which. The Stinkbug nymphs have a "black bump on their butt." The Assassin Bug nymphs have no such bump.
Also, unlike the Stinkbug(s) and nymphs which travel in herds, the Assassin Bug, true to his/her name, travel alone. Subsequently, you will usually encounter them one at a time -- maybe two, but probably no more than two at once...
Last spring, I didn't have a SINGLE bug on any of my tomato plants in buckets standing around the perimeter of my yard. Upon examination, I encountered the Assassin bugs that were munching on the Mexican Heather? which grew along the same perimeter. The love the stuff! They also kept every single bug off of my plants, the whole season.
[quote="stephanietx"]Thanks! I don't like that it was chowing down on one of the few ladybugs I have in my garden...[/quote]
Unfortunately, the predatory insects don't distinguish between pest species and other predator species. But it's worth keeping them. And you can't buy them (at least, I've never seen them for sale anywhere).
Gymgirl, you say they were "munching" on the Mexican heather. But they don't have any mouthparts for "munching". Were they possibly after the nectar? Or were they actually feeding on the plants by sucking the sap?