Quick facts
- The squash bug is a common pest of squash and pumpkins.
- Young seedlings and plants that are flowering are most vulnerable to squash bug feeding.
- They can cause young plants to wilt and die.
- Squash bugs cause little damage to plants in late summer and fall.
- Squash bugs can be managed through a combination of nonchemical steps and pesticides.
How to identify squash bugs
Adult squash bugs (Anasa tristis) are flattened, large insects.
- They measure 5/8 inch long.
- They are usually dark gray to dark brown.
- Their abdomens have alternating orange and brown stripes.
- The eggs are oval-shaped, 1/16 inch long, and yellowish to bronze.
- The nymphs hatching from the eggs range in size from 1/10 to 1/2 inch long as they progress through five stages called instars.
At first, the young nymphs have a light green abdomen and black heads and legs. As the nymphs grow larger, they first turn light gray and then brownish-gray, with black legs and antennae.
Biology of squash bugs
Squash bugs can live through the winter as adults in sheltered places, such as under plant debris, around buildings, or under rocks. When adults come out in the spring, they fly to growing cucurbit plants to feed and mate.
Female squash bugs lay small clusters of eggs (about 20) on the undersides of the leaves, especially between the veins where they form a V. Eggs may also be seen on stems. The females usually start appearing in gardens in early June and continue to lay eggs through mid-summer.
Eggs hatch in about 10 days, and nymphs mature in about four to six weeks. Both adults and nymphs hide under leaves when disturbed.
One generation develops each year, although in some summers there may be a partial second generation.
The life stages overlap and all stages can be seen at any given time during the growing season. In the fall, especially after the vines have died, the adults and nymphs group together on squash fruits.
The adults fly or crawl to sheltered places for the winter. The nymphs die when temperatures drop to freezing.
Damage caused by squash bugs
Squash bugs primarily attack squash and pumpkins, although they can also attack other plants in the cucurbit family, such as cucumbers.
- They suck the sap out of leaves with their piercing-sucking mouthparts. Their feeding causes yellow spots that eventually turn brown.
- The feeding also affects the flow of water and nutrients, and, when severe, can cause wilting.
- Unlike cucumber beetles, squash bugs do not carry diseases.
- Larger, sturdier plants are more tolerant of feeding damage, while young plants may die because of feeding.
Managing squash bugs in home gardens
Cultural controls
- Maintain healthy, sturdy plants through proper fertilization and watering to help limit squash bug damage.
- Remove plant debris during the growing season to reduce sites where squash bugs can hide.
- Clean up cucurbits and other plant matter in the fall to reduce the number of overwintering sites.
Physical controls
- Crush eggs that are attached to the undersides and stems of leaves.
- Remove and kill nymphs and adults by dropping them into a pail of soapy water. This is practical only if a few plants are affected.
- Removing squash bugs can be challenging because squash bugs hide under leaves and move quickly when disturbed.
- Trap squash bugs by laying out boards or pieces of newspaper. Squash bugs will group under the boards at night; you can then collect and destroy them in the morning.
Using pesticides
Insecticides are normally not required to manage squash bugs.
Managing squash bugs on farms
Monitoring
- Start scouting for egg masses in July.
- Treatment is most effective on freshly hatched nymphs, so monitoring egg numbers helps in timing effective controls.
- Consider treatment if you find an average of one egg mass per plant.
- Eggs hatch 7-10 days after being laid.
Cultural controls
- Squash bug adults spend the winter in plant debris. Remove crop residues and keep field borders mowed and free of debris.
- If squash bugs are a consistent and severe problem, avoid straw mulches, which give squash bugs the extra shelter they seek at night.
- Some varieties of squash are more tolerant of squash bug damage. Studies have shown that butternut and buttercup squash, and sweet cheese pumpkins tolerate squash bug feeding more than other varieties.
Trap cropping can be used to draw squash bugs outside of the planting. Studies have shown perimeter plantings of blue hubbard squash can draw squash bugs out of crops. The trap crop should still be managed to reduce squash bug populations through thorough egg squashing or insecticide application.
Physical controls
Eggs can be scraped off leaves and squashed during scouting.
Chemical controls
- Chemical controls are most effective on nymphs. Scouting helps time insecticide applications for shortly after nymphs hatch.
- Nymphs often hide on the underside of leaves, so good spray coverage is important
- This pest is active when vine crops are flowering, so remember to protect pollinators when selecting products and making applications. Apply later in the day when flowers are closed.
For insecticide control options, see the Midwest Vegetable Production Guide.
Reviewed in 2024