Natural Enemies Gallery

Assassin Bugs

Hosts or Prey

Mostly small to medium-sized insects and other small invertebrates

Identification

Assassin bug adults and nymphs (immatures) have an elongate head and body and long legs. The narrow head has rounded, beady eyes and long, hinged, needlelike mouthparts. Adults and nymphs can walk rapidly when disturbed or capturing prey. Adults tend not to fly.

Coloration varies greatly by species. Adults can be blackish, black and orange, a mix of colors (e.g., black, brown, green, and reddish), or brownish, grayish, or pale overall. Adults range from about 1/5 to 1-1/4 inches (5–30 mm) long, varying by species. In comparison with the relatively parallel-sided abdomen of Zelus spp., the abdomen of Sinea spp. is wider near the rear.

Nymphs can be pale or dark colored overall or have coloration resembling adults of the species. They are wingless, but developing wings (wing pads) of older instars are oblong and partially cover the abdomen.

Eggs of the leafhopper assassin bug, Zelus renardii, are oblong and dark brown. They have a white cap and occur in groups glued to plant surfaces. Eggs of the spined assassin bug, Sinea diadema, are also oblong and brown with a pale top, but after deposition each egg cap unfolds to form a fringed corolla or umbrellalike cover.

Lookalikes

Zelus nymphs can be confused with young instars of leaffooted bugs, Leptoglossus spp. (Coreidae). These bugs can occur together because assassin bugs prey on the plant-feeding leaffooted bugs. Zelus nymphs have pale-colored legs and antennae. Nymphs of leaffooted bugs have dark-colored antennae and legs. As they grow, leaffooted bugs become easily recognized by the expanded, flat (leaflike) area on the hind legs.

Thread-legged bugs (Reduviidae: Emesinae) and certain other groups have a distinctly different appearance. Thread-legged bugs are long and thin overall and can be confused with stilt bugs (Berytidae), such as the predatory spined stilt bug.

Life Cycle

True bugs develop through three life stages. Eggs hatch into wingless nymphs, which develop through five, increasingly larger instars (immature stages). The last instar develops into a winged adult without any pupal stage.

Assassin bugs typically have one or two generations per year. Overwintering varies by location and species. Assassin bugs in the Zelus genus commonly overwinter as adults, which may be observed on walls and windows during fall when they seek shelter.

Habitat

Assassin bugs can occur on almost any terrestrial plant including row and tree crops and gardens and landscapes. All species are predators of invertebrates or true parasites of vertebrates. Most assassin bugs feed on insects including caterpillars, larvae of leaf beetles and sawflies, and adults and nymphs of other true bugs. Nymphs and adults ambush or stalk prey, impale them with their tubular mouthparts, inject venom, and suck the body contents. Zelus renardii produces a sticky material that helps it adhere to plant surfaces and ensnare prey.

Assassin bugs are not considered to be important in the biological control of pests, unlike predatory groups such as bigeyed bugs and minute pirate bugs. Assassin bugs are general predators and also feed on bees, lacewings, lady beetles, and other beneficial species. Certain species feed on the blood of birds, mammals, or reptiles, including conenose bugs and kissing bugs (Reduviidae: Triatominae).

Species

About 7,000 species of assassin bugs are known in the world. There are at least 13 genera of assassin bugs in California, including 4 or more species of Zelus. Zelus renardii is common throughout California and the Western Hemisphere; it closely resembles Z. tetracanthus, which in California is found mostly in natural areas. At least 6 species of Sinea occur in California, including the similar-looking Sinea confusa and S. diadema.

More Information

Scientific classification:

  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Hemiptera
  • Suborder: Heteroptera
  • Family: Reduviidae
Adult spined assassin bug, Sinea diadema.
Adult spined assassin bug, Sinea diadema. Credit: Jack Kelly Clark, UC IPM Program
Appearance and relative size of adult assassin bug, Zelus sp.
Appearance and relative size of adult assassin bug, Zelus sp. Credit: David Kidd
Adult assassin bug, Zelus sp.
Adult assassin bug, Zelus sp. Credit: Jack Kelly Clark, UC IPM Program
Eggs of the leafhopper assassin bug, Zelus renardii.
Eggs of the leafhopper assassin bug, Zelus renardii. Credit: Jack Kelly Clark, UC IPM Program
Assassin bug, Zelus sp., nymph.
Assassin bug, Zelus sp., nymph. Credit: Jack Kelly Clark, UC IPM Program