Authors: David Lowenstein, Russell Groves, and PJ Liesch UW-Madison Entomology
Revised: 01/30/2026
Item number: XHT1135

Squash bugs (Anasa tristis) are an emerging problem in Wisconsin.  In recent years, these insects have become more prevalent, causing damage to vine crops in home gardens and commercial fields alike.  Squash bugs feed on a wide range of cucurbit crops, but pumpkins and squash are their preferred hosts, followed by gourds and melons.

Appearance

Adult squash bugs, which often congregate in large numbers, are ¹/₂ to ³/₄ inch long, mottled brownish-black and somewhat flattened.  They give off a strong odor when crushed.  Immature squash bugs (nymphs) initially have dark heads and legs with pale green bodies.  Older nymphs have grayish bodies.  Squash bug eggs are ¹/₁₆ inch in diameter and reddish-orange to brown in color.  They are often laid in clusters on the undersides of leaves along the center vein. Both adults and nymphs possess needle-like mouthparts, which they use to suck fluids from plants.

Symptoms and Effects

Adult and immature squash bugs feed on plant juices and release toxins into leaves.  Early symptoms of an infestation include yellow spotting on the leaves.  Leaves may eventually become dry and brown or black along the edges.  Feeding can also cause wilting which can resemble bacterial wilt (see University of Wisconsin Garden Facts Bacterial Wilt of Cucurbits for details).  Young plants are more susceptible to severe damage.  Later in the season, adults will also feed on developing fruits, which may stop developing and begin to rot.

Life Cycle

Adult squash bugs overwinter in Wisconsin in protected areas (e.g., amongst plant debris, firewood piles, in wooded areas or along fence rows).  Adults mate after they emerge in the spring and females lay eggs in late June and early July when vine crops begin to develop.  Eggs hatch after about 10 days.  Nymphs undergo five molts over a period of four to six weeks before reaching maturity.  New adults appear in late July and early August.  There is only one generation of squash bugs per year in Wisconsin, but because females lay eggs over an extended period of time, all life stages may be present on plants simultaneously.

Scouting

The key to managing squash bugs is early detection.  Although it is unusual to find large populations of squash bugs early in the season, be sure to check transplants and new seedlings for adults.  Squash bugs tend to hide on the undersides of leaves where they are sheltered and may be difficult to find and control.  A degree day model (see University of Wisconsin Garden Facts Degree Day Calculation for details) can be used to predict the development of squash bugs.  Using a base temperature of 58°F, eggs will appear at 193 degree days (DD) and nymphs will emerge at 554 DD.  Inspect the undersides of leaves for squash bug eggs beginning in early July and continue with regular scouting into September.

Management of Squash Bugs

Non-chemical management: Many non-chemical approaches can help manage squash bugs:    

• Eliminate overwintering sites: Remove/destroy plant debris from your garden or production field in the fall to reduce the number of overwintering adults. Burn, bury or hot compost these materials. Destroying plant debris from areas adjacent to your garden or production field can also help limit squash bug overwintering.
• Crop rotation: Since squash bugs only feed on cucurbit crops, crop rotation over space and time can be part of an overall management strategy in some situations. (see University of Wisconsin Garden Facts Using Crop Rotation in the Vegetable Garden for details)  
• Harborage traps: Squash bugs are often found on the undersides of leaves during the day, but will go to other sheltered locations. In small-scale plantings (e.g, home gardens) consider placing a board, old shingle, or similar item on the ground to provide a hiding spot for squash bugs. Squash bugs will congregate at night under the boards and can then be collected each morning and killed by dropping them into a bucket of soapy water.
• Trellising: Consider trellising vine crops where possible, as trellised plants are less susceptible to squash bug infestations.
• Delayed planting: Overwintering squash bugs prefer larger, more established plants. Thus, planting later could help deter activity of squash bugs.
• Hand-removal and squishing: In small-scale settings, hand-picking, squishing, or knocking squash bugs into a container of soapy water can be a consideration. Keep in mind that squash bugs prefer to hang out on undersides of leaves, and they can move quickly. While inspecting plants, look for and crush clusters of the reddish-orange eggs.

Chemical management: When plants are in the seedling stage, treat if plants are visibly wilting and squash bugs are present.  In older plants, the treatment threshold for squash bugs is one egg mass per plant during the period when plants are flowering.  Apply foliar applications of registered insecticides when eggs are hatching to target nymphs, which are more easily controlled by insecticides than adults. 

Home gardeners have a number of spray options available, including organic options such as insecticidal soaps, horticultural oils (e.g., neem oil) and pyrethrins. Conventional sprays for homeowners include ingredients from the pyrethroid group (e.g., cypermethrin, permethrin, etc.) and carbaryl.

For commercial production, refer to the UW-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for a list of registered insecticides and management recommendations.

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