The insect is a harlequin bug, found commonly on plants in the cabbage family (among others).

Are you fighting oleander aphids on milkweed that you've been growing for the monarchs? If so, squishing is about your only recourse, since I'll bet that your plants are covered up with caterpillars and/or monarch eggs.

No, the aphids came along with (I think, unless they arrived shortly after) a plant that was planted with the cleome. They are so plentiful that I didn't even notice them before. I don't see any caterpillars or monarch eggs on them, just tons and tons of these guys.

Any aphids you have came from your soil and they are easy to control with a sharp water spray that knocks them off the plant.

If you have properly identified oleander aphids, then you will find them on milkweed plants in your location and not anything else. Click on the attached image for comparison.

I've found that these particular aphids are quite resistant to sprays of water from the hose unless you REALLY spray the heck out of the plants. Most people cultivate milkweed cultivars to provide the important host plant for Monarch butterfly caterpillars (seen in the image) so attacking those durn aphids that way can't be done if the plants are loaded up with monarch eggs or caterpillars. That's why squishing can be helpful.

Here is a link that might be useful:

I am surprised that no one suggested aphid parasites Aphidius sp. or ladybug larva (they look like tiny Gila monsters) for your aphids. Here in Florida a person can look for other plants with aphid infestations and collect leaves that have large numbers of aphid mummys or ladybug larva. If done in the evening, either or both beneficial insects will quickly (a week or so) take care of problems like the one you are having without harming the butterflys.
You can check out this link. If it works (I'm not very good at links) or just Google or Yahoo Aphid parasites. They are expensive to buy, but free to collect.

www.cdpr.ca.gov/docs/pestmgt/ipminov/ben_supp/aphidp&p

This would not be the time of year in zone 7 to introduce parasitic or predatory control measures. It hardly seems appropriate for one plant, anyway, when squishing can take of them at zero cost and about 10 seconds' time. ;-) Also, the cardinolides found in milkweed and other Asclepiads protect the aphids against predators. These pesky critters have quite a little niche for themselves!

Kimmsr, these aphids aren't found in the soil.