Aphids are small sap-sucking insects that can appear on plants and can cause damage to leaves, flowers, and stems. There are several factors that can lead to the appearance of aphids, including weather conditions, plant stress, and a lack of natural predators. Warm and dry weather conditions can provide optimal conditions for aphid reproduction. Plant stress caused by drought or other environmental factors weakens the plant's defenses against pests. Additionally, a lack of natural predators, such as ladybugs or lacewings, can allow aphid populations to grow unchecked. Once they appear, it is important to take prompt action to control the infestation before it causes significant damage to your plants.