Billbugs
Billbugs are small weevils, 1/4 to 1/2 inch long, with a curved snout. In the northern US the bluegrass billbug attacks Kentucky bluegrass, ryegrass and fescues. In the South the hunting billbug attacks zoysia and Bermuda grass. The adults do little harm; their legless larvae hollow out grass stems, then chew the crowns and roots, and the turf dies in patches from late June. The test is simple: pull the dead stems. If they snap at the soil and are full of sawdust-like frass, it is billbug. Purdue puts them in about half of Indiana's home lawns, and healthy turf carries modest numbers without damage.
A legless billbug larva and frass in a split grass stem. Photo: pending.
Identification
Adults are hard, grey to black or reddish-brown weevils with a long curved snout and elbowed antennae, often coated in soil. They are easiest to find walking on driveways, pavements and kerbs in spring. The bluegrass billbug (Sphenophorus parvulus) is about 1/4 inch (7–8 mm) with evenly spaced pits on the thorax. The hunting billbug (S. venatus) is 8–11 mm, dark reddish-brown, with a raised, smooth Y-shaped mark on the thorax. Purdue also lists the lesser and unequal billbugs, and Utah the larger Rocky Mountain billbug.
Larvae are cream-white and legless, with a brown head, and grow to about 1/4 to 1/2 inch (6–12 mm). Having no legs separates them from white grubs, which have three pairs of clearly visible legs and grow larger, up to 1½–2 inches. Young larvae are found inside the stems; older ones lie in the crowns and among the roots, and Purdue finds overwintering hunting billbug larvae in the top 2–3 inches (5–7.5 cm) of soil.
Easily confused with
- White grubsAlso a pestBillbug damage is often blamed on grubs. White grubs have three pairs of legs and grow larger, up to 1½–2 inches; billbug larvae are legless, 1/4–1/2 inch, and start out inside the grass stems.
Damage symptoms
Adults chew small notches and holes in stems and lay their eggs in them, which does little harm. The damage is from the larvae, and it shows from late June into August in the North. It is easily taken for drought, dormancy, disease, compacted soil or grubs. The difference is that billbug-damaged stems break off at the soil line, while grub-damaged turf lifts off in a mat because the roots below have gone.
- Small dead spots about 2–3 inches (5–8 cm) across from mid-June, joining into large irregular patches
- Straw-coloured turf that does not green up when watered
- Stems that snap off at the soil when tugged, hollow and packed with sawdust-like frass
- Warm-season lawns: zoysia or Bermuda grass slow to green up in spring after last year's damage
- Small snouted weevils walking on paths and driveways in spring
Lifecycle & degree days
The bluegrass billbug has one generation a year, with a partial second generation in some years that does not survive the winter. Adults spend the winter in thatch, leaf litter and soil cracks, become active in April and May once the soil reaches about 65 °F (18 °C), and lay eggs in holes they chew in the stems. Larvae feed inside the stem, then drop to the crowns and roots; they complete development in five to eight weeks, and new adults appear from late July to September. The hunting billbug overwinters as adults and larvae, and in south Georgia every stage can be found all year.
- Generations
- 1 a year, sometimes a partial 2nd (bluegrass billbug); hunting billbug 2–3 overlapping in Texas and Florida (Texas A&M), up to 6 reported from Florida (UGA)
- Adults active
- Late April to mid-May, soil above about 60–65 °F (Ohio, Pennsylvania)
- Egg hatch
- About 6 days (Ohio)
- Larval feeding
- 35–55 days (Ohio); 5–8 weeks (Pennsylvania)
- Damage shows
- Late June to August
- New adults
- Late July to September
Host crops
The bluegrass billbug prefers Kentucky bluegrass and also takes perennial ryegrass, fescues and grain crops. The hunting billbug is the southern species and does most harm in zoysia and Bermuda grass; Texas A&M adds St. Augustine, centipede and bahia grass. Zoysia cultivars differ: in Texas trials Zoysia matrella types such as 'Diamond' and 'Zorro' resisted it, and Z. japonica types such as 'Meyer' and 'Palisades' did not.
Monitoring & action thresholds
Ohio State and Utah State both treat one larva per cup-cutter sample as the point to act. Penn State gives an economic threshold of 6–8 larvae per square foot. Purdue is more relaxed: larval counts of 10 per ft² are common, and healthy turf tolerates them without obvious damage. Sources disagree, so judge by the tug test in patches that are actually failing.
In spring, watch pavements, driveways and kerbs on warm days for adults, or sink a plastic cup into the turf with its lip level with the soil as a pitfall trap and check it weekly. From mid-June, tug stems at the edges of any yellowing patches and cut cores 3 inches (7.5 cm) deep to look for larvae. Growing degree-day models time the stages well: Purdue puts first adult activity at about 280 degree-days (base 50 °F), Ohio State at 280–352.
Biological control
Insect-parasitic nematodes are the biological control with the best evidence against billbugs. Grewal's turf review rates Steinernema carpocapsae and Heterorhabditis bacteriophora equally and says treating larvae works better than treating adults. Purdue matches them to the stage: S. carpocapsae for adults at the surface, H. bacteriophora for larvae in the root zone. Georgia's 2025 circular is more cautious and calls their reliability questionable. Ground beetles, rove beetles, ants and spiders eat billbugs, and in the East a tiny wasp, Anaphes calendrae, parasitises many of the eggs. Commercial Beauveria fungus preparations exist, but Ohio State says the fungus rarely kills enough billbugs to affect the population.
Cultural controls
The most reliable long-term answer is grass that billbugs do not like. Endophytes, fungi living inside some ryegrass and fescue plants, make the grass distasteful, and several Kentucky bluegrass cultivars resist billbugs.
- Overseed with endophyte-enhanced perennial ryegrass, tall fescue or fine fescue; Purdue suggests at least 40% endophyte-infected plants
- Choose resistant Kentucky bluegrass cultivars, such as 'Park', 'Arista', 'Kenblue', 'Delta' or 'NuDwarf'
- In the South, prefer resistant zoysia types such as 'Zeon', 'Diamond' or 'Zorro'
- Water and feed properly so turf hides mild to moderate damage
- Do not bring in sod from an infested Bermuda or zoysia lawn
Chemical, last resort
Sources
Purdue Extension E-266, Managing Billbugs in Turfgrass (Richmond, 2022)
Ohio State Ohioline HYG-2502-12, Billbugs in Turfgrass
Penn State Extension, Billbugs in Home Lawns
Utah State Univ. Extension, Billbugs in Turfgrass (Wickwar & Ramirez, 2022)
UGA Extension Circular 1173, Hunting Billbug: Biology and Management in Turfgrass (2025)
Texas A&M AgriLife, Landscape IPM: Hunting Billbug
Grewal, Using entomopathogenic nematodes for turfgrass pest management, Turfgrass Trends (2001)
Pacific NW Extension PNW 544, Using Entomopathogenic Nematodes for Crop Insect Pest Control
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Billbugs by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.