Greenhouse Insects to Look out for This Gardening Season

It’s the peak of the gardening season when the green-fingered among us are deeply immersed in the business of tending our plants. One inevitable obstacle that every gardener must overcome, however, is the menace that is greenhouse pests.

Insect invasions are often bad news for crops, as many greenhouse bugs cause significant damage to the plants they feed on. Certain pests may even transfer diseases to your plants, which can completely destroy all the hard work you put into those tomatoes.

Staying vigilant is an important part of greenhouse pest control. If you tackle the problem as soon as it arises, you’re far less likely to end up battling a full-blown infestation!

But what are the most common greenhouse pests, and how can you identify them?


What are they?

Whitefly is a very common greenhouse pest and is widespread throughout the United States. These tiny, moth-like insects are also sap-suckers, and can cause significant damage to your plants if left unchecked!

What do they look like?

There are many different species of whitefly, all of which look very similar to one another. Whiteflies are tiny, winged insects that look very much like little white moths. They are closely related to aphids, mealybugs, and scales and, like these insects, have piercing, sucking mouthparts that they use to feed on plant sap.

How can you spot them?

Like aphids, whiteflies are most commonly found on the underside of plant leaves. By sucking sap from the plant, they can cause stunting, wilting, yellowing, reduced fruit yield, and even plant death. They also secrete honeydew, which creates perfect conditions for the growth of sooty mold fungus.

One easy way to check for whiteflies is the give the stems of your plants a gentle wobble. If there are whitefly present, they will give themselves away by rising up in a little white cloud.

Fungus gnats

What are they?

Fungus gnats are a species of small fly that is most often found living in plant pots, the soil around plants and compost. These chewing bugs feed on the roots of plants which, in the case of severe infestation, can lead to stunted growth.

What do they look like?

Fungus gnats look like tiny flies with long legs and antennae and grey wings. They are dark in color and usually measure 1/16 – 1/8 inch long.

How can you spot them?

Though fungus gnats can fly, they don’t tend to move around that much. These weak flyers are more likely to be found running across the soil surrounding plants, particularly in plant pots. You may also notice eggs or larvae; elongated, whitish grubs with black heads. If these larvae are present in large numbers, they may leave slime-trails (similar to those of snails) on the surface of the soil.


What are aphids?

Aphids are small, soft-bodied insects that feed on plant sap. To do this, they use specially adapted mouthparts to first pierce the leaf and then suck out the sap.

What do they look like?

There are around 30 different species of aphid that are commonly found in greenhouses, and all differ slightly in appearance. However, they are generally less than 1/8-inch-long with long legs and antennae, and two tube-like projections (called cornicles) sticking out the rear end. Aphids vary widely in color and may be brown, black, yellow-green, dark green, gray, yellow or pink.


How can you spot them?

Aphids will often congregate on the underside of leaves, where is it easier for them to access the plant’s sap. The insects themselves may be tiny, but the destruction they cause is easy to spot. Plants with a heavy aphid infestation will often have a mottled, yellow appearance, and the leaves may begin to wilt. Aphids also secrete a sweet, sticky substance called honeydew, which encourages the growth of black, sooty mold.


What are they?

Thrips are tiny, sap-feeding insects that lay their eggs inside the leaves of the plants they infest. They have rasping mouthparts which they use to puncture the leaves of plants and get at eh sap within. These bugs target a wide range of greenhouse plants, and a large infestation can cause significant damage.

What do they look like?

Thrips are small insects, measuring around 1/25 inch in length. They have four wings and are brown or black in color.

How can you spot them?

Thrips usually hang out in the buds, flowers and leaf axils of plants, so they can be difficult to spot before the effects of the infestation have become apparent. The damage thrips cause to plants is often widespread and can include deformed leaves and blossoms, reduced fruit and vegetable yield and white or silver speckled leaves. Thrips also excrete brown droplets on the petals and leaves of plants as they feed, which darken to black as they dry.

Spider mites

What are they?

Another type of sap-sucking insect, spider mites are tiny bugs that target a wide range of greenhouse crops. Their piercing, sucking mouthparts can cause widespread damage to plants as they extract the sap from leaves.

What do they look like?

Spider mites are very small bugs that usually measure no more than 1/50 inch in length. The two-spotted spider mite is one of the most troublesome mite species that can invade your greenhouse this summer. They are green in color and, as the name suggests, they have two distinctive dark spots on their abdomen.

How can you spot them?

Two-spotted spider mites suck sap from the underside of leaves, so this is where they’re most likely to be found. The draining of sap from these leaves can give them a speckled appearance, and heavy infestations can cause the leaves to dry out completely and fall off. Spider mites also leave a distinctive webbing everywhere they go, which can be seen draped over the leaves and flowers of infested plants.


Greenhouse pests can wreak havoc on your plants if left unchecked. This gardening season, be on the lookout for the most common pests that can invade your greenhouse, such as aphids, thrips, whitefly, fungus gnats, and spider mites. Catching these critters early can give you the head start you need to prevent a serious infestation from taking hold!


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We are a team of experts in various fields who have come together to help you get rid of pests quickly and efficiently.

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