By James A. Bethke.
In the fall, a common call I receive from friends and neighbors concerns masses of bright red bugs on trees, shed walls or front porches. I’ve experienced the same thing at my house, masses of red bugs on the faces of our concrete steps and hiding in mass under boards or between piled bags of soil amendment. While investigating the occurrence, I found that one of these red bugs was an invasive bug (Scantius aegyptius), one that does not belong here and invaded from another country, and that there are many common local species that can be mistaken for the invasive.
Seed bugs or red bugs are true bugs in the insect Order Hemiptera (Heteroptera). When an entomologist says ‘bug’, they mean species in the Order Hemiptera, and everything else is an insect and not necessarily a bug. True bugs have piercing sucking mouthparts, so some of them are predators, some feed on plants, and some can do both. Seed bugs can be found feeding on seeds and seed pods from different plants, and sometimes they are host specific.
One common seed bug is the small milkweed bug, which feeds on seed pods of milkweed like this one in our butterfly garden (Figure 1). Other red bugs that can be mistaken for each other include large milkweed bug, red shouldered bug, box-elder bug, red bug, white-crossed seed bug, painted bug, harlequin bug, some assassin bugs, and some others without common names.
The invasive species is called the red bug, Scantius aegyptius, which originated in the Mediterranean region and invaded Southern California back in 2009. Once established, they proliferated in our environment, which resembles the Mediterranean climate. The most common host plant they have been associated with in our area is cheese weed or malva. In my backyard, I witnessed small immature red bugs holding malva seeds straight out in front of them on their beaks. The seed was almost as big as the nymph, and they would carry them, stumbling, as they tried to run away. They weren’t holding the seed with their legs. They had pierced the seed with their proboscis and raised the seed out in front of them.
Red bugs aggregate most likely due to a pheromone. They will overwinter as a group then disperse when new plant growth occurs, and seeds are produced. For those of you that are concerned about the masses of red bugs and what to do about them, I need to remind you that they are not a plant pest, they are more likely a nuisance pest simply because of their presence and numbers. So, if they are a nuisance and you want to get rid of them, I do not suggest spraying them with insecticides. I recommend getting out your vacuum cleaner and sucking them all up, bagging them, and getting rid of them in the trash. If you have milkweed bugs, your plants are suffering, and you love monarchs, then spraying them with a low rate of insecticidal soap will be the best you can do, and it will have minimal effect on the monarch larvae.
James A. Bethke is the Floriculture and Nursery Farm Advisor Emeritus for San Diego and Riverside Counties.
The Floriculture and Nursery Farm Advisor Emeritus conducts applied research, education and outreach programs to improve production and viability of the floriculture and nursery industries in San Diego and Riverside Counties.
Jim's program emphasizes the integrated pest management of major pests of floriculture and nursery production. He collaborates with regulators, growers, and other scientists on advisory committees that set policy based on science.