While houseplants are generally easy to care for, there are some common pests that you may run across. Here's a quick look at them:
Mealy Bugs-these pests look like tufts of cotton and attack a wide variety of plants. They particularly seem to like Dieffenbachia and Coleus. They are usually found where the leaves join the stem, and sometimes can be found in the roots as well. They suck juices out of the stems, weakening the plant and eventually killing it. To treat, moisten a cotton swab with rubbing alcohol and wipe them off. Repeat a week or so later in case any eggs were left behind. If you have a severe infestation you can spray the plant with an insecticide made for houseplants (check labels carefully!). If you have root mealies, wash all the soil off of the roots and repot in fresh soil.
Aphids- these are the scourge of many a houseplant lover. They come in many different colors, black, gray, orange, and green. You'll find them clustered on the undersides of leaves, on flower buds and growing tips, and where the leaves meet the stem. Like Mealy Bugs, Aphids suck the juices out of plant stems and deposit a sticky substance known as honeydew. When a plant is severely infested it's not unusual to find the surfaces around it coated in it, and honeydew attracts another common pest-ants! If you find ants around where you have houseplants, it's likely you have an aphid problem. Luckily they are easily treated. Simply take the affected plant and give it a shower under the tap, or if it's a large plant, in the tub, and let the water knock them off and drown them. If the infestation is particularly bad, you can spray with an insecticide made for houseplants.
Scale-this is a more problematic pest. Scale insects attach themselves to the undersides of leaves and are protected by a hard outer shell, making insecticidal sprays useless. Like aphids, they secret honeydew. For light infestations you can wipe them off with a cotton swab or damp cloth. For more involved infestations, try spraying with Neem oil. If an infestation is heavy and the plant has begun to turn yellow, disposal is the only option.
Fungus Gnats- these are more of a nuisance than a pest. They are tiny black flies often found flying around plants. Getting rid of them is easy as they live only in overly moist soil. Simply water less often and they will disappear. If you have fungus gnats it's a sign you're over watering your plants. If they are particularly troublesome, unpot the plant, wash the soil from the roots and repot in fresh soil.
Whitefly- these tiny, moth-like insects are quite troublesome. If you have them, you know it-every time the affected plant is moved, they rise above it in a great cloud before resettling on the plant. Whitefly usually occurs in large numbers and spread quickly from plant to plant. Like aphids and scale they suck juices out of the plant and deposit honeydew. Getting rid of them is difficult, if spraying every three days with an insecticide meant for houseplants doesn't work, the plant should be disposed of.
Spider Mites- these are tiny spider-like insects that are hard to see with the naked eye. The first sign of infestation are white webs that appear between leaves and stems. They thrive in hot dry conditions so it's important to keep your plants well humidified. Mist leaves regularly, especially in winter when central heating dries out the air. To treat an existing infestation, give the plant a shower under the tap or in the tub, and repeat in a week or so. If infestation is advanced to where the plant is losing leaves, spray with an insecticide meant for houseplants.
Despite the pests discussed above, many houseplant owners will never have to deal with any of them. To prevent infestations, choose new houseplants carefully. Look under the leaves and at the stems for signs of insects. Isolate new plant purchases until you're sure they are insect free-and isolate any houseplants you already have that may be infested until treatment is complete. Most pests attack weak plants, so keeping your plants healthy and happy is the best thing you can do to prevent insect attacks!