Carabidae
Ground beetles- Kind
- Wild — attract it
- Best for
- Background predation near the soil
Pest
Squash bug
Anasa tristis
The short answer
A flat, grey-brown sap-feeding bug about 15 mm long that attacks squash and pumpkin above all, and other cucurbits less often. Adults and nymphs feed on the leaves, which become speckled and then turn yellow and brown. Heavy feeding wilts whole runners, and young plants can die. Adults are difficult to kill with sprays, so garden control is about crushing the bronze egg clusters and dealing with the young nymphs.
hero macro · adult and egg cluster on leaf underside
Adult Anasa tristis beside a bronze egg cluster on a squash leaf underside. Photo: pending.
Identification
Adults are 14–16 mm long, flattened, and dark grey-brown to almost black. The reliable tell is the edge of the abdomen, which sticks out beyond the wings and has alternating orange and brown stripes. They hide near the crown and under leaves, and run for cover when disturbed.
The eggs are easier to find than the bugs. They are bronze to brick-red ovals about 1.5 mm long, laid in clusters of around 20 (from a few to more than 40) on leaf undersides, often in the V where two veins meet. Newly hatched nymphs are light green, with a dark or reddish head and legs. As they grow they turn grey, and the older ones often look dusted with white powder.
Easily confused with
- Leaf-footed bugsAlso a pestLeaf-footed bugs have a flattened, leaf-like blade on each hind leg and often a white zigzag band across the wings; squash bugs have plain legs.
- Stink bugsAlso a pestStink bugs are wider and rounder; squash bugs are longer and narrower, about a third as wide as they are long.
- Wheel bug nymphsBeneficial — leave itWheel bug nymphs are red with black legs; squash bug nymphs are pale green when young, later with a blackish thorax and brownish abdomen, often dusted with white powder.
Damage symptoms
Squash bugs suck sap and inject a toxic saliva as they feed. Large, vigorous plants tolerate a good deal of it. Seedlings, and plants under heavy attack at flowering, can lose whole runners or die. In one field study, summer squash invaded at flowering and fruit set and left untreated lost more than half its yield. Overwintered adults can also carry the bacterium that causes cucurbit yellow vine disease.
- Yellow speckles on the leaves that turn brown
- Runners or whole plants that wilt, then blacken and go crisp at the feeding point — Anasa wilt
- Seedlings that collapse after heavy feeding
- Scarred or misshapen young fruit, and rot on the undersides of fruit lying on the ground
- Bronze egg clusters under the leaves, and grey nymphs gathered near the crown
Lifecycle & degree days
Adults spend the winter under debris, boards, rocks and in woodpiles, then fly to cucurbits in spring to feed, mate and lay eggs. In Minnesota the females arrive in early June and keep laying into midsummer. Because egg-laying goes on for weeks, eggs, nymphs and adults are all present at once for most of the season. The number of generations depends on the climate: one in Minnesota and Connecticut, sometimes a partial second, and two to three in California and other warm regions. The degree-day figures below come from a single study (Fargo and Bonjour 1988), cited in a 2016 peer-reviewed review.
- Lower threshold
- 58 °F / 14.4 °C (upper 92 °F / 33.3 °C)
- Per generation
- 747 degree days °F (~415 °C)
- Generations / yr
- 1 in the north, 2–3 in warm regions
- Overwinters
- Adults, under garden debris
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Host crops
A pest of cucurbits. Summer squash and pumpkin are strongly preferred for egg-laying, and bugs survive better on them than on cucumber or melon. That preference is why squash planted as a trap crop can draw them away from melons and cucumbers. Some winter squashes are less attractive or more resistant, including butternut and Royal Acorn.
Monitoring & action thresholds
Action threshold
1 egg mass per plant
This is a commercial summer-squash figure (Doughty et al. 2014); another study uses one adult per plant. UC IPM notes that no threshold has been set for California. In a home garden, what matters is timing: control counts most on seedlings and at flowering, and University of Minnesota advises that late-summer and autumn feeding does not need treatment, however many bugs you see.
From the time plants go in, turn the leaves over and look for bronze egg clusters. UC IPM advises checking young plants daily. Crush any clusters you find. Lay boards or pieces of newspaper on the soil near the plants: the bugs shelter under them overnight and can be collected in the morning. The weeks around flowering matter most, because that is when numbers on the plants are highest.
Beneficial
Biological control
The two natural enemies with published parasitism rates are both wild. The egg parasitoid Gryon pennsylvanicum, a scelionid wasp, parasitised 66% of squash bug eggs collected on two Virginia farms in 2013. The feather-legged fly Trichopoda pennipes, a tachinid, lays its eggs on large nymphs and adults; reported parasitism is about 20% of bugs collected in late summer in Connecticut and 12% in coastal Virginia. Cornell's biocontrol guide says it may reach 80%, but parasitised bugs keep feeding and laying eggs for some time, so the fly does not always prevent crop damage. The fly now has its own page: tachinid flies; the egg wasp does not. Generalist predators — spiders, ground beetles, big-eyed bugs and lady beetles — also eat squash bug eggs, nymphs and adults. Pyrethroid sprays harm these natural enemies as well as pollinators.
Hippodamia convergens and others
Ladybugs- Kind
- Wild — attract it
- Best for
- Background predation on eggs and nymphs
Tachinidae
Tachinid flies- Kind
- Wild — attract it
- Best for
- Parasitises large nymphs and adults; about 12–20% in field surveys
Cultural controls
In a garden, physical control and early timing do more than any spray. UC IPM's verdict is that stronger insecticides are unlikely to beat hand-picking combined with the softer products.
- Cover young plants with row covers and remove them at bloom so the flowers can be pollinated
- Crush egg clusters on leaf undersides and stems as soon as you see them
- Lay boards near the plants and collect the bugs that shelter under them each morning
- Clear crop debris, boards and old fruit after harvest to remove overwintering shelter
- Skip straw or other organic mulch where squash bugs have been a problem — it gives them cover
- Grow less-favoured types such as butternut or Royal Acorn, or plant squash as a trap crop beside melons
Chemical, last resort
Adults shrug off most sprays — aim at young nymphs, and never spray open flowersCheck any product before it goes on. Open the compatibility matrix →
- Insecticidal soapREI 12 h
- PyrethrinsREI 12 h
- EsfenvalerateREI 12 h
- Lambda-cyhalothrinREI 24 h
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
Doughty et al., Squash Bug: Biology and Management in Cucurbitaceous Crops, J. Integr. Pest Mgmt 2016
UC IPM Pest Notes 74144, Squash Bugs (Rijal & Schellman, 2025)
UC IPM Pest Management Guidelines: Cucurbits — Squash Bug (text updated 2016)
UC IPM, Relative Toxicities of Pesticides Used in Cucurbits to Natural Enemies (2016)
University of Minnesota Extension M1208, Squash Bugs in Home Gardens (2007)
University of Georgia IPM, Squash Bug fact sheet (2020)
UConn Home and Garden Education Center, Squash Bug fact sheet (2018)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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