The monsoon season that lasts from early July to September brings desperately needed and much appreciated bouts of heavy rainfall to the excessively hot and arid Sonoran Desert. During the summer months in Arizona, daytime temperatures regularly exceed 100 degrees Fahrenheit, and the relative humidity rarely rises above 25 percent in desert cities like Tucson and Phoenix. Unsurprisingly, it is not uncommon for arthropod pests to seek refuge in air-conditioned homes during the hottest and driest days in Arizona. The arthropod pests that invade Arizona homes most frequently in response to unfavorable climatic conditions include Arizona bark scorpions, cockroaches, millipedes, ants, and ground beetles.
Once indoors, these insect pests, and many others, gravitate toward the nearest dark and well concealed spaces that are moist enough to provide immediate relief from disagreeable outdoor weather. Many arthropod pests that invade homes to escape summer heat and drought are strictly outdoor-dwelling herbivorous species that have not adapted to survive within human dwellings. These less common pests are frequently referred to as “occasional invaders,” and they rarely manage to secure the resources and conditions they need to survive and reproduce within homes. The most common occasional home-invaders in Arizona include millipedes, ground beetles, springtails, root weevils, elm-leaf beetles, and sowbugs.
The insects commonly known as “Palo Verde root borers,”, or simply “Palo Verde beetles,” (Derobrachus geminatus) emerge from backyard lawn soil in massive numbers at the start of the monsoon season, and they remain major nuisance pests that bite humans on residential properties until the arrival of fall. These beetles are among the most hated landscape pests, as the soil dwelling larvae or grubs of this species damage and kill trees and shrubs by feeding on woody roots and internal plant fluids for a period of three to four years. Larval specimens are almost never encountered since they remain hidden within moist soil surrounding the base of woody plants, but adults are easy to recognize because they look like unusually large cockroaches. Brown to jet black adult Palo Verde beetles are massive in size, as they range from 3 to slightly more than 3 ½ inches in body length. Their midsection is outfitted with conspicuous spines and they also possess noticeably long antennae and prominent pincer-like mouthparts that deal out frequent, painful, but harmless bites on human skin.
Have you ever sustained a bite from a Palo Verde beetle?