Plant Problem Diagnostic
Asparagus Beetle: Identification and Control
The short answer
The common asparagus beetle is metallic blue-black with about six cream to yellowish spots, while the spotted asparagus beetle is reddish-orange with twelve black dots.
The common beetle lays small dark eggs on the spears and its gray, black-headed larvae plus the adults chew spears and later the ferns, and severe fern damage can reduce next year's spear production.
In home gardens, handpick adults and larvae into soapy water and destroy eggs, and harvest spears promptly and completely to keep larvae from establishing.
In fall, clean up plant debris and weeds around the planting to remove the sites where adults overwinter.
Telling the two species apart
The common asparagus beetle is a metallic blue-black beetle with six cream-colored to yellowish spots on its back, about a quarter inch long.
The spotted asparagus beetle is reddish-orange with twelve small black dots. Its orange larvae bore into and feed on the berries, so the spotted species is generally less damaging to the edible spears than the common species.
Eggs, larvae and the damage they do
The common asparagus beetle lays small dark eggs attached to the spears and ferns; the University of Maryland describes them as very small black eggs inserted into the spears.
The gray, black-headed, somewhat slug-like larvae and the adults both feed, disfiguring and scarring spears and browning them, and both feed on the ferns. Illinois Extension notes that severe fern damage can reduce spear production the following year.
Cultural control and sanitation
- 1Handpick — In small plantings, handpick the beetles and larvae into a pail of soapy water and destroy eggs before they hatch.
- 2Harvest clean — Harvest spears promptly and completely, which helps prevent larvae from establishing, and cut spears quickly after they reach eating size.
- 3Fall cleanup — Keep weeds and debris out of the planting and clean up all plant debris at the end of the season to remove overwintering sites for adults.
If a product is needed
When populations are high on a larger planting, Extension sources list options such as neem, pyrethrum or pyrethroid insecticides applied according to the label.
Reserve any spray for spears and ferns with heavy larval pressure rather than routine treatment, and rely first on handpicking and sanitation in a home garden.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Illinois Extension — Asparagus Beetle — Verifies the common beetle is bluish-black with six cream-colored elongate spots and the spotted beetle is reddish-orange with twelve black dots; that the common beetle lays eggs on spears and ferns; that larvae are gray with a black head and slug-like; and that both larvae and adults feed on ferns, with severe fern damage reducing spear production the following year, plus handpicking and destroying eggs.
- Iowa State University Extension — How do I manage asparagus beetles? — Verifies the metallic blue-black common beetle with six yellowish spots and reddish-orange spotted beetle with 12 spots; dark green to gray black-headed grub-like larvae feeding on shoot tips and foliage; disfigured, scarred, brown shoots; that keeping weeds and debris out reduces overwintering sites; that prompt and complete harvest prevents larval establishment; and that handpicking suits small plantings.
- University of Maryland Extension — Asparagus Beetles (Vegetables) — Verifies very small black eggs inserted into the spears, gray larvae feeding on spears, handpicking adults and larvae or controlling with a botanical insecticide (neem, pyrethrum), cutting spears quickly after they reach eating size, and cleaning up all plant debris and weeds at the end of the season to remove overwintering sites.