Arugula insect infestation
I am unable to identify the insect. I don't have the resolution to zoom in to count the legs, determine body structure. Can you estimate the size? Describe coloration ( appears leaf green or tan). When did it first appear? Does it hop, jump. or fly? Is it causing damage by biting or chewing the leaves either the leaf edge or making holes in the leaves. The most common insects that are found on arugula are: flea beetles, leaf miner (under side of leaves will have left a trail), aphids ( cluster in groups ) thrips and others.
Hazarding a guess what your photo shows is most like thrips. You do not want to use an insecticide on produce. What you can try is an insecticidal soap or neem oil. If, these measures do not solve your problem please e-mail again and ask for bug identification resource and your question will be forwarded to the proper expert.
I hope that I have been of some help.