Spotting something – or many somethings – creeping across the leaves of a beloved new plant can be alarming. More alarming still is not knowing whether a creepy crawly is harmful to plants – especially if the plant in question is ornamental or expensive. Of course, not all creepy crawlies are harmful – some are beneficial and worth keeping around. This guide should provide some insight into the good, the bad, and the ugly of indoor pests.
Aphids
The sap-sipping plague of the everyday gardener, aphids will attack plants in any setting, given half the chance. They will be familiar, perhaps, to anyone who has ever taken a stroll through the park or sat outside during the summer: tiny pear-shaped bugs with a set of antenna and a smaller set of tubes at their rear ends, these pests display a wide variation of colours, but usually come in green or black. It is a comfort to know that aphids are usually wingless and will therefore have trouble spreading if plants are not overcrowded, but – to spite this comfort – aphids will evolve to grow wings if populations are overcrowded, so it’s important to control aphid infestations as early as possible.
Some aphids will feed on any common plant they can find, whilst others exclusively feed on a specific plant. Those growing food should be especially vigilant, as aphids which feed on specific and commonly grown foods such as citrus and cabbage are quite common. Aphids like fresh produce and will suck sap and other juices from anywhere in the plant but are most commonly found on the undersides of leaves.
The presence of aphids among plants can be spotted upon examination of the leaves, which may begin to turn yellow or exhibit shrivelling while still in season. As aphids are sap-sippers, they produce honeydew, a sticky sap, and this can cause a sooty mold to develop on the surface of leaves.
It is a comfort to know that aphids can be simple to get rid of: a thorough spray of cold water onto the affected plant followed by application of a cold water and dish soap solution onto the affected leaves is often more effective than an insecticide in controlling aphids. However, in the case of aphids which have spread disease, sometimes the only option is to sacrifice the plant.
Those who are outdoors can try to attract certain predators to their gardens in order to control aphid populations: ladybugs and lacewing flies are common predators but controlling a wildlife population out in the open is quite difficult. Indoor gardeners can try to introduce more plant biodiversity to their gardens: catnip is known to repel aphids (and will make any house cats very pleased), and garlic and chives can be grown near plants such as broccoli or cabbage to detract aphids with specific tastes. Often, however, the best prevention is to thoroughly check a plant before purchase, as this is where most infestations begin.
Mites
Mites on plants are nearly invisible to the naked eye. Often, the quickest way to identify an infestation is to shake the plant over a piece of plain paper, which – if infestation is present – will cover the paper in black or red specks. Thankfully, mites can’t fly (but they are notorious jumpers).
Mites suck on plants, which can produce hard galls over leaves and prevent effective growth. Spider mites, which are the most common indoor mite, will cover the tips of leaves with a white net-like substance. Mites are parasites and some species will feed on animals (including humans) as well as plants, which means it is important to remove mites as soon as possible. Mites particularly enjoy feeding on trees and shrubs.
To control an existing mite population, non-toxic oils are quite effective. Doing this is much more beneficial than using an insecticide, which may kill some of the natural controllers of mites and other non-harmful insects. Dousing a plant with cold water may cause some existing populations to drop from leaves.
The best way to prevent infestation of mites is to thoroughly check a plant before purchase. New plants should be quarantined even if no infestation is detected, as eggs are not always visible.
Mealybugs
Another sap-sipper (see aphids for a description of what sap-sippers do), mealybugs also secrete a fluffy white substance onto the undersides of leaves. The mealybugs or their eggs may be found under this substance. Mealybugs are quite small, but just about visible to the naked eye, usually growing to a maximum size of half a centimetre. They are usually oval-shaped. Males are winged and quite mobile, but females have no wings and are slow-moving.
Most mealybug species unfortunately target common household plants including ferns, orchids, and succulents. Some mealybugs also target roots, which can cause plants to wilt quite rapidly as damaged roots cannot take in nutrients as effectively as they should. Mealybugs may also spread plant diseases.
In the first instance, visible colonies should be removed from the plant as soon as possible. After this, a hardy plant which can survive the cold can be placed on a windowsill during winter as mealybugs cannot survive outside of temperate climates. On the plant’s return indoors, common fatty acids and plant oils can be used as organic pesticides. In summer, the plant can be quarantined and treated with the same organic pesticides – but if the infestation is heavy, the best thing to do may be to sacrifice the plant.
As usual, the best prevention is to check the plant thoroughly before purchase and quarantine it upon introduction into the home.
Whitefly
Whiteflies are usually no bigger than three millimetres, meaning it is difficult to identify them by their signature patterned wings or long legs. However, they usually present in clusters on the undersides of leaves, which makes them a great deal easier to spot.
Another sap-sipper, whiteflies may not be visible until they fly off a leaf. As such, it is important to regularly check leaves for honeydew even if whiteflies are not immediately visible. Whitefly infestation should be caught early as whitefly larvae feed as soon as they hatch and – as a female whitefly can lay up to 400 eggs – this can be devastating to a plant.
Spraying a plant with cold water will remove live insects from the plant. Whilst they are gone, coat the plant’s leaves in a mixture of washing-up liquid and water, which should repel the whitefly population. This should only be done when it is cool outside. For tenacious populations, the Farmer’s Almanac recommends using a handheld vacuum to forcibly remove populations.
Natural predators for whiteflies are common in the household – a house spider is an excellent first defence and often really quite friendly, so it’s worth not killing them. Ladybugs and dragonflies are also natural predators, but are not as easy as a house spider to keep in an indoor garden.
Scale Insects
Scale insects vary from being nearly invisible to measuring at over a centimetre in size. Adult scale insects don’t move much, but nymphs are quite active. Adult scale insects can be identified by their waxy shells.
As sap-sippers, all of the above applies for scale insects. Owners might also notice shells appearing on the undersides of plants – these are the scale insects themselves.
The kindest way to deal with scale insects is simply to scrape them off, as this will deal with a normal infestation and will prevent killing any harmless scale insects. For larger scale insect infestations, persistent application of plant oils and fatty acids should solve the problem.
The best way to prevent the spread of scale insects (aside from parasitoid wasps, which are almost certainly unwelcome houseguests in themselves) is to quarantine the affected plant. Carefully remove infested leaves, and new growths should be infestation-free.
Thrips
Thrips are less than a millimetre in size and are as such almost invisible to the naked eye. They are difficult to identify, especially to non-entomologists, and can devastate not only houseplants, but furniture and carpets. Some thrips are capable of flight.
Thrip presence on a plant can be observed in patches of scarring on leaves, which can be bronze or silver. This is due to the thrip’s feeding on the plant’s undigested food, which causes plant cells to collapse. Some species of thrip will also lay eggs inside the plant itself. Some thrips will also create galls in leaves.
Thrips are incredibly difficult to control. The solution offered for the whitefly is known to be effective in some cases but – for the most part – knowledge of how to control thrip populations is full of gaps. If a thrip infestation is identified, it is usually best to get rid of the infested plant before the infestation can spread to other plants or – in the worst case scenario – furniture.
To Conclude
Most infestations in indoor plants begin before money has even exchanged hands between the buyer and the vendor. It can be difficult to identify mild infestations in store, especially if the pests aren’t yet hatched or are in the larval stage, which is why quarantining new plants for a month is so important. A house spider (or a few house spiders!) can be a first line of defence against some of these pests, so it’s worth keeping them around. Plant owners should stay vigilant, particularly in the summer months, and keep some plant oils or fatty acids tucked away. Keeping plants can be rewarding, but plants are as vulnerable as animals to infestations and illnesses, so prevention and treatment are key to keeping a healthy garden.
More Information
The Farmer’s Almanac – https://www.almanac.com/gardening/pests-and-diseases
The Farmer’s Almanac provides comprehensive information on a variety of pests and diseases, and also offers plenty of advice for optimising a harvest. Whilst it is geared towards outdoor gardens, its advice is nonetheless sound.
Royal Horticultural Society – https://www.rhs.org.uk/advice/advice-search?sortReverse=false&sort=_score&facets=2;12
The Royal Horticultural Society is a UK charity whose advice on gardening is widely accessible. It comes in the form of fact files and advice sheets which makes information easy to take in. Like the Almanac, it is geared towards outdoor gardens but is nonetheless helpful.
