Aldona Bird, Contributors, Latest News

Scale insects can do some damage to house plants

Unfortunately, my love of plants does not always result in good gardening.

Last year as the weather got cold, I brought my plants in from the porch — where they had thrived through the summer without much care from me. For the first couple of winter months I took pretty good care of them.

Then I started watering them less frequently. There were only a few casualties of the consequent drought and the low light conditions of my house.

Worse than those hardships was the scale. It attacked one spider plant a few years ago, and spread to neighboring spider plants.

Scale are insects that feed on plant sap. Their numbers can rapidly increase and cause significant damage to plants. The name scale can refer to any of over 8,000 species of these insects.

True to their name, scale often look like blemishes or ahem scales on a plant. A protective waxy substance covers them. Although I’ve seen them often, I’ve never noticed any distinguishable body parts.

I haven’t yet identified the scale species on my house plants, but they are oval and rounded, smooth, beige and the larger ones not much more than an eighth inch long. The smaller ones are flatter and almost translucent.

They leave a sticky substance on my plants when infestation gets bad. They appear to belong to the hard shell scale category (mealy bugs are an example of soft shelled scales), but I read that hard shelled scales usually don’t leave sticky residue, called honeydew. Perhaps mine are an exception, or perhaps they only leave noticeable stickiness when they have increased to particularly large numbers.

Female scales lay eggs underneath their bodies, providing protection. The eggs hatch into nymphs or crawlers. These move away from the mother, finding a new spot to feed. Once they lock onto a spot on the plant with their mouth parts, they transform into their immobile adult forms.

The males however, turn into gnat-like flying insects. It amazes me that scale has two such different adult forms.

Occasionally I cleaned off all the scale I could find using a Q-tip dipped in rubbing alcohol, but of course I’d miss some. My neglectful behavior resulted in only episodic cleaning so I could never quite get rid of them.

Last winter the scale multiplied more rapidly, spreading to a couple other plants, including an aloe. They killed some branches of the spider plants and some aloe leaves.

When I moved them outside this spring, I swore I would work harder to get ride of the scale. My plan was to spray all affected plants with Safer’s soap. But I dallied — and then noticed that the scale seemed to be receding.

I noticed ants on the plants with scale, and wondered if they were helping. I learned that they are, but not by eating or removing the scale — they are eating the honeydew (the excrement insects leave behind). This is helpful because honeydew causes mildew growth on the plants.

Natural controls including inclement weather (I’ve wondered if heavy rains have knocked off the scale) and predators such as ladybugs and parasitic wasps may help reduce scale on plants kept outdoors.

Whatever the reason, I’m glad of it as it buys me a little break from feeling guilt for not cleaning off the critters manually. I hope this year to take better care when I bring my plants back indoors, and not allow the scale to build up in numbers again. I also hope to water my plants consistently.

ALDONA BIRD is a journalist, previously writing for The Dominion Post. She uses experience gained working on organic farms in Europe to help her explore possibilities of local productivity and sustainable living in Preston County. Email