Rove beetles
Rove beetles are the largest beetle family in California, with over 1,200 species there. They are slender, with wing cases so short that most of the abdomen is exposed, and some hold the tail curled up. They range from 1 mm specks to the devil's coach horse at over an inch. Most hunt tiny prey in compost, leaf litter and topsoil: fungus gnat and root maggot larvae, mites and fly eggs. One, Aleochara bilineata, also parasitises root maggot pupae. You keep them with mulch, compost and no broadcast soil insecticides, and Dalotia coriaria is sold for greenhouses.
At a glance
- Kind
- Wild — attracted, not bought
- Size
- 1 mm to over 1 in (25 mm)
- Tell
- Short wing cases; bare abdomen, sometimes upturned
- Lives in
- Compost, leaf litter, topsoil, damp debris
- Eats
- Fly larvae, mites, eggs; some eat fungi or decay
- Species
- Over 1,200 in California alone
How it works
Rove beetles are built for moving through litter and soil. The wing cases are short, so most of the abdomen shows, and some, such as Oligota, have a pointed abdomen that curves upward at the rear and a head bent down under the body. Most are predators or parasites of tiny arthropods in organic debris and topsoil, and prey depends on species: ants, aphids, bark beetles, immature flies, mites or termites. Some feed on decaying matter, fungi or pollen instead. In turf, rove beetles, ground beetles and ants cause substantial mortality of Japanese beetle eggs and young grubs.
A few are specialists worth naming. Aleochara bilineata is an important enemy of cabbage and seedcorn maggots: adults eat the eggs and larvae, and the larvae parasitise the pupae. Oligota oviformis, about 1 mm long, eats spider mites in coastal California orchards; each larva takes about 20 mites a day and each adult about 10. At the other end of the scale, the devil's coach horse (Ocypus olens) is over an inch long and is a snail and slug predator in some California gardens, although UC IPM notes it also feeds on ripening and decaying fruit and vegetables. The greenhouse species Dalotia coriaria is reared and sold for fungus gnats.
What it is confused with
Rove beetles are easily taken for earwigs. One small group, Paederus, can burn the skin, so brush rove beetles off rather than crushing them.
- PestEarwigs — Earwigs carry a pair of forceps-like pincers at the tail. A rove beetle has none, although it may curl its tail up.
- Also goodPaederus rove beetles — A rove beetle genus. Crushing one on the skin releases a toxin, pederin, that causes burning, line-shaped lesions. Wash the skin at once.
- Also goodGround beetles — Usually shiny black, with ridged wing cases. Also a predator, and hides under rocks by day.
How to keep it around
Rove beetles live where organic matter is damp and decaying, because that is where their prey breeds. In a South Carolina trial, plots mulched with cover-crop residue caught more rove and ground beetles than bare, tilled plots in at least one year.
- Mulch beds with straw, leaves or cover-crop residue rather than leaving the soil bare
- Keep a compost heap and some leaf litter under shrubs
- Leave stones, boards and pots at bed edges for shelter
- Avoid broadcast soil insecticides; UMass warns that soil-dwelling beetles are susceptible to them
Pesticide sensitivity
UMass warns that soil-dwelling ground and rove beetles are susceptible to insecticides, and advises against broadcast soil treatments where they are controlling root maggots. Open the compatibility matrix →
When to choose something else
Wild rove beetles are a background check in soil and compost. Look elsewhere when:
- Fungus gnats are swarming houseplants or seedlings — use a drench of Bti or Steinernema feltiae, and let the compost dry between waterings
- You want rove beetles in a greenhouse on purpose — buy Dalotia coriaria
- Root maggots hit your brassicas or onions every year — a row cover at planting keeps the flies off
- Slugs are the problem — UC IPM finds most slug predators rarely effective enough for garden control, and the rove beetles recorded eating slugs mostly take eggs and hatchlings
Rove beetles by target
What it eats and when it turns up differ by pest. Each page below is the picture for one target.