Aphids come in a multitude of colors. In a way, black aphids are great because you can notice them maybe a bit quicker than you would an aphid that is matching the color of your plant!
What are the black bugs on this plants?
I dove into the research and found that Aphids are very much likely to be the culprit today! Other resources showed pictures and videos of the same bug you are experiencing on your chard, and all have matched my hypothesis to be black aphids!
To eradicate the pest:
Since this infestation is larger, I would start by gently rinsing the plant off while avoiding washing the pests back into your soil to prevent reproduction and another infestation.
Mix 1-2 teaspoons of soap per 16 oz spray bottle of water. That also means you will always have hand soap in your garden! (These sprays will not work on chewing insects such as leaf miners or caterpillars)
Simply give the leaves and stems a good coat of whichever spray you choose and let dry in the shade to prevent sunburn. Neither of these sprays is harmful to bees. After a couple of days, you may want to come back and rinse the rest of the dead aphids and live aphids that may have lingered.
If that spray did not work to the extent of your liking, you will want to go in with a stronger organic spray. One of the sprays that would work is Neem Oil. This is an organic spray that is derived from the seeds of a neem tree! You just have to be cautious of the wet product coming in contact with bees.
This means you should spray in the late afternoon, or spray and cover with a shade cloth, or spray and even place in your garage or shed if possible for the first hour of the product drying. This will also prevent sunburn.
Neem Oil only cares for soft-bodied insects and will not kill bugs like caterpillars.
If you would like to have a spray on hand that cares for not only the insects like the aphids you have, but leaf miners, caterpillars, and more… Captain Jacks Dead Bug Brew would be the way to go. This is an organic spray derived from a bacterium found in the soil! The same precaution for protecting bees must be used when spraying with this product.
Before using Neem Oil or Captain Jacks Dead Bug Brew we recommend starting with a spray like Castile Soap or Safer Soap, this helps keep the beneficial insects thriving. Neem Oil and Dead Bug Brew are only recommended to be used up 10 -15 times a year.
All of these sprays can be bought at a local nursery or hardware store.