University of Illinois Extension

Living with Your Houseplants and their Insect Relatives

Everyone has guests over at the house once in a while and some stay a few days. We do all we can to bring our houseplants indoors for the winter without the “insect relations” that so often accompany the plants and never leave, said Richard Hentschel, U of I Extension horticulture educator.

“Sometimes even after our best attempts you wake up some morning a few weeks after your houseplants have been inside and see something that is not quite right on the plants or maybe in the window trying to get out,” said Hentschel. “The insects we find are not always closely associated with our houseplants, but rather happened to be on the plants at the time they were brought in.

“If this is the case, the potential for a problem is really low. These insects do not feed on our plants and without food, and in the wrong environment; we will find them dead on the window sill if we have not already disposed of them with paper toweling or the vacuum cleaner hose and nozzle.”

Box elder bugs are a great example, they will wander around the home, living on the food they have stored and you will find them later not having survived being indoors. Box elder bugs also leave behind little black spots of the food they digested, so keeping up with them is preferred rather than having to do a cleanup later.

“The insects that are troublesome outside are the ones that will cause the problems on the inside as well,” he said. “Outdoors there are natural predators that will keep the populations in check and weather events like rainstorms that also help reduce the number of insects on the houseplants.

“Inside the house we don’t have rain events and without natural predators, the offending insects grow their numbers quickly, living on the houseplants.”

Two of the more common houseplant insects during the winter months are spider mites and scale insects. Spider mites can come in several colors, yet the feeding damage is all the same. Spider mites do not have chewing mouthparts. They feed by scratching the plant tissue and feeding on the plant sap. Mites can also spread digestive juices in the feeding area, destroying more tissue for consumption.

“Mite damage will sneak up on you as insects start out on the underside of the leaves and in low numbers,” Hentschel explained. “Later as their numbers explode you will see them near the vegetative growing points and flower buds by the thousands among very fine webbing. When you find them this way, you know you have a really good outbreak going on that needs immediate attention.

“You can rinse off the nymphs and adults with forceful streams of water, using the sink attachment in the kitchen or give them a shower in the bathroom if the plant is too big for the kitchen sink. Plan on doing this again after a few days as the left over eggs will hatch and start the process all over. The goal is to break the life cycle and not let an adult lay any more eggs. If you do that, you win!”

The second common houseplant insect that can survive indoors and your attempts at getting rid of them before you bring them indoors are scale insects. Scale insects live and feed on the houseplants and as time allows indoors, will increase in numbers too. The best “tell” that you have scales will be a clear sticky material on the leaves or a sticky mess on the floor below the plant on the hardwood or carpet.

“Scale insects insert their feeding tube into plant tissue and begin to remove the plant sap to feed on,” he said. “As they feed on the plant sap, the excess is expelled and drips downward where we see it as that shiny sticky surface. The adult scale is firmly attached and protected on the plant stems. The offspring is a very small fleshy insect resembling an aphid and can be dislodged just like spider mites. The adults take a lot more effort as they are protected by their scale. Getting rid of scale insects is a lot more work than spider mites. You may end up resorting to a safe for use inside, insecticide labeled for use on houseplants.”

These two common insects are above ground insects and you may find something else in the pot itself. Pillbugs, also called roly poly bugs (because they roll up into a ball) love humidity and feed on organic matter and are often found inside your potted plants. You will not see them until you water the houseplant, temporary forcing them out of the pot. Earwigs will be another insect that is common in the potting soil. A thorough watering will force them out of the pot. Be sure to do this in an area that the bugs can be rinsed away and not return to the pot.

On occasion there can be an outbreak of even the common aphid indoors. Aphids give live birth, so using the rinse nozzle on the kitchen sink or the bathroom shower will usually take care of the problem.

“There will be an added benefit of all that plant rinsing- clean plants means more photosynthesis and healthier plants since they will not be covered with household dust,” he said. “One of the better things we can do during any holiday season is to separate the holiday gift plants from the general population of houseplants. This helps guarantee that your houseplants remain insect-free.”