Asparagus beetle
Two leaf beetles that feed on asparagus. The common asparagus beetle, about 1/4 inch long and blue-black with cream spots and red edges, chews the spears so they scar, brown and bend into a hook, and glues rows of dark eggs to the tips. Its grey larvae and the adults then strip the ferns, which weakens the crown for next year. The spotted asparagus beetle is orange with 12 black spots; its larvae eat the berries and do little harm. In a garden, hand-picking, harvesting promptly and cutting out the dead ferns in autumn are the main controls, and lady beetles and a tiny wild wasp help keep numbers down.
Adult Crioceris asparagi with eggs on an asparagus spear. Photo: pending.
Identification
The common asparagus beetle is about 1/4 inch (6 mm) long and elongated. It is metallic blue-black with a red thorax and red borders to the wing covers, which carry cream-yellow spots. Minnesota Extension counts six spots; Maryland describes four. Its larvae are soft, slug-like and grey to grey-green with a black head and legs, and reach about 1/3 inch (9 mm). The eggs are the easiest thing to find: tiny, about 1 mm, shiny and dark, stood on end in rows on the spears.
The spotted asparagus beetle is orange-red with 12 black spots, six on each wing cover, Minnesota gives 1/4 inch for both species; Maryland puts the spotted one slightly larger, at about 1/3 inch. It is easily mistaken for a lady beetle, but it has a longer, more elongated oval body. A lady beetle is rounder and more dome-shaped, with the head partly or completely hidden when seen from above, and shorter antennae. The spotted species' larvae are orange and feed on the asparagus berries.
Easily confused with
- Lady beetlesBeneficial — leave itThe orange, 12-spotted asparagus beetle is often taken for one. It has a longer, more elongated oval body; a lady beetle is rounder and dome-shaped, with the head partly or fully hidden from above and shorter antennae.
Damage symptoms
The adults feed on the spear tips as soon as they come up, and the spears turn brown, scarred and bend over into a hook. Eggs on the spears do no harm in themselves, but they put people off eating them. After harvest, adults and larvae of the common species feed on the ferns. Stripped ferns cannot store enough food for next year's spears, and Minnesota Extension notes that a thin canopy also leaves the plants more open to Fusarium. Young beds suffer most. The spotted species' larvae eat only the berries and do not harm the plant.
- Spear tips scarred, browned and bent into a shepherd's-crook hook
- Rows of tiny dark eggs stuck upright on the spears
- Ferns chewed bare, with grey slug-like larvae on them
- A weakened crown and poorer growth the following season after heavy fern feeding
Lifecycle & degree days
Adults overwinter in hollow asparagus stems and plant debris, and come out as the first spears emerge in spring. Females lay eggs on spears, ferns and flower buds. The eggs hatch in about a week, and the larvae feed for about two weeks, then drop to the ground and pupate in the soil. New adults emerge 5–10 days later and start the next generation. There are two generations a year in Maryland. The spotted species arrives later, in mid-May in Minnesota, and is gone by late July.
- Egg hatch
- About 1 week, depending on temperature
- Larval feeding
- About 2 weeks
- Pupa
- 5–10 days, in the soil
- Generations / yr
- 2 in Maryland
- Overwinters
- Adults, in old stems and debris
Host crops
Both species are pests of asparagus, and the extension sources describe no other crop host. The spears are at risk during harvest and the ferns afterwards. Newly planted beds are the most vulnerable, and Maryland Extension suggests treating them more often to help them establish. UC IPM notes that the beetles are found wherever asparagus is grown, but are not normally serious pests in California.
Monitoring & action thresholds
Minnesota Extension's garden thresholds: act if 10% or more of plants carry adults of either species, if 50–75% carry common asparagus beetle larvae, or if 20% or more of spears carry eggs. Commercial spear thresholds during harvest are 5–10% of spears infested or 2% with eggs (Minnesota) and 10% infested or 1–2% with eggs (Maryland). After harvest, Minnesota's fern threshold is 50–75% of ferns infested.
Start looking as soon as the spears come up in spring, and keep checking through the season. The beetles are most active on warm, sunny afternoons, so that is the time to count them. Check spear tips for adults and eggs during harvest, and the ferns for larvae afterwards.
Biological control
The most important natural enemy is wild. Tetrastichus asparagi, a tiny metallic-green wasp, parasitises asparagus beetle eggs, and Minnesota Extension says it can kill up to 70% of them. It is not sold and has no page here yet. Lady beetles, both adults and larvae, and other generalist predators eat the eggs and small larvae. Minnesota's advice is to leave these beneficials alone. Most insecticides labelled for asparagus are broad-spectrum and remove them too.
Cultural controls
In a garden bed, hand work and hygiene are usually enough.
- Hand-pick adults and larvae into a pail of soapy water, and rub the dark eggs off the spears
- Harvest spears promptly and regularly, before beetles have time to lay on them
- Leave a few plants at the edge to grow into ferns early: the beetles gather and lay there, away from the spears you are picking
- Cut out the ferns in autumn once they are completely brown, and clear the debris the adults overwinter in
- If snow comes before the ferns have browned, remove the dead ferns as early as possible in spring
Chemical, last resort
- CarbarylREI 12 h
- PermethrinREI 12 h
Sources
University of Minnesota Extension, Asparagus beetles (Schuh, Hahn & Wold-Burkness, rev. 2026)
University of Maryland Extension, Asparagus Beetles (Yurchak, Vegetable & Fruit News)
UC IPM Pest Management Guidelines: Asparagus — Asparagus Beetles
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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