Assassin Bugs: Why They Are Good for the Garden

Red and black insect with spiny black legs on a green leaf

David Alexander / Flickr / CC BY 2.0

Assassin bugs are a group of predatory insects including up to 150 different species, whose habitats range across the continental United States. True to their name, assassin bugs are formidable insects that can spell trouble for many other insects. They're also, in some cases, dangerous for humans. It's good to get acquainted with the different insects that fall under this description, so you can determine which ones may be beneficial in your garden, and which ones should be approached with caution.

What Are Assassin Bugs?

Assassin bugs are not one specific insect but belong to a category made up of a number of different types of predatory insects, in the Reduviidae family. They typically target caterpillars, bees, and flies. The one physical feature these predators have in common is a "weapon": a long proboscis that acts as a sort of dagger or sword. This elongated mouth part injects a paralyzing toxin into the prey insect's body, and then after the insect is immobilized, that same mouth part is used to suck the body fluids of the "victim" like soda being sucked through a straw. This method of attack is also what can lead to the potential spread of dangerous parasites. Assassin bugs tend to breed in autumn, and some varieties of them can live for several years.

How to Identify Assassin Bugs

Assassin bugs are such a varied group that there's no singular identifying feature. The elongated proboscis mentioned is one feature that many of them have. The Zelus genus comprises a number of assassin bug species. One commonly seen in the southern US, in Texas in particular, is the milkweed assassin bug, Zelus longipes, recognizable for its distinctive red and black coloring. Assassin bugs are often brightly colored, denoting their dangerous bite. But some are sneaky. One group of assassin bugs known as "ambush bugs" sits perched on flowers, camouflaged by the colors of flower petals, lying in wait for their unsuspecting victims.

Assassin bugs tend to have long, tubular shaped heads, which makes them look like they have a long "neck." Many of them are winged but they're rather clumsy at flying. They tend to have small protruding eyes and long spindly legs. Their lightweight form means it is relatively easy to "flick" them away if they land on or near you, and makes it less likely they'll bite you for trying to crush them.

Where They Are Found

Assassin bugs are known virtually across the entire continental United States, but are most prevalent in the South and warmer regions that allow them to proliferate for a longer portion of the year. One commonly seen type of assassin bug in the southern US (in Texas in particular) is the aforementioned Zelus longipes, recognizable for its distinctive red and black coloring. Indeed, many assassin bugs have bright colors, possibly nature's warning that that their bites can be dangerous. But many of these bugs are muted shades of brown or grey.

Also found in Texas is the kissing bug or cone nose bug (Triatoma) which has a tiny head and a large flat oval shaped body about the size of a penny with short pale yellow or orange stripes on the side of the lower abdomen. These bugs have piercing, sucking mouth parts and they feed on blood, using a gentle, painless bite in the facial area (hence the name "kissing bug") to extract their meal. These bugs originate in Latin America (including Mexico) but have increasingly been found in Texas, and they can carry a parasite that can cause Chagas' disease in humans and dogs. The concern over this disease is such that public health officials are doing their best to notify citizens in affected areas.

Why Assassin Bugs Are Helpful in the Garden

 Assassin bugs are considered beneficial for the garden because they help to control harmful insects that might devour foliage, such as caterpillars or grasshoppers. They're drawn to vegetable gardens, ornamental flower gardens, and orchards, and can be useful in controlling insects that tend to devour these plants and crops.

Dark grey bug with ridged crest and long legs on leaf

Mike Axelrod / Flickr / CC BY 2.0

What Are the Drawbacks to Assassin Bugs?

Despite their usefulness as predators of common nuisance insects in the garden, assassin bugs have drawbacks too. Some assassin bugs are harmful to humans, due to their tendency to bite and/or the potency of their venom, and some, like the kissing bug, carry harmful parasites.

The wheel bug is one such nasty assassin variety; it's a very large grey bug usually just over an inch long, with a circular crest on its back. These rather daunting looking bugs usually go after grasshoppers and caterpillars in the garden. If handled or accidentally held, they will tend to bite and the bite is immediately painful, though not harmful in the long term. Topical analgesics and bite treatments can be used to alleviate the pain and disinfect the area.

It is very important to contact a physician and/or get emergency medical care if there is any sort of allergic reaction to an insect bite or sting, such as generalized swelling, itching, hives, or difficulty breathing.

Prevention and Control

Despite the somewhat alarming possibility of insect bites, generally speaking, assassin bugs are not found in large numbers in most gardens, and their presence is more likely to be beneficial than harmful. It's not recommended to try and control them with insecticides. By providing a welcoming garden environment, you can help the assassin bugs do their "job" of eliminating destructive insects like aphids and caterpillars. Mulch gives them a place to hide and take cover, and lighting at night attracts them to the garden (assassin bugs usually will not go after light-loving moths, however).