Aphids
Aphids are small insects that feed on foliage.
They’re very small, often only a millimeter long. They suck the juices out of infested plants.
Their feeding will often distort the leaves. While feeding, they leave a sweet substance, known as honeydew. Honeydew often gets moldy and turns black. This often makes leaves and branches look like they’re covered in soot. Therefore, this “sooty mold” is a very noticeable symptom of aphid infestations. Also, since the honeydew contains sugars, ants will often be attracted to heavily infested plants.