Colorado experiences a noticeable abundance of moths, particularly during certain times of the year. The presence of these numerous insects is a natural occurrence, influenced by specific species, the region’s diverse environmental conditions, and their biological life cycles.
Understanding Colorado’s Abundant Moths
The perception of a large number of moths in Colorado is primarily due to a specific species: the Miller Moth, scientifically known as Euxoa auxiliaris. These moths are the adult stage of the army cutworm. Miller Moths are typically gray or light brown, with a wingspan ranging from 1.5 to 2 inches, and they often display wavy dark and light markings on their wings, including a distinctive kidney-shaped spot on the forewing.
While Colorado is home to approximately 1,000 known moth species, the Miller Moth accounts for the vast majority of the “swarms” noticed by people. They are most prevalent in late spring and early summer, though the exact timing and duration of their presence can vary each year.
Environmental Conditions Supporting Moth Populations
Colorado’s varied landscape and climate create a suitable environment for large moth populations. Moths originate from the plains, including eastern Colorado and neighboring states like Wyoming, Nebraska, and Kansas.
The presence of diverse vegetation across different elevations in Colorado offers abundant food sources. Adult Miller Moths primarily feed on nectar from flowers, and they seek out these floral resources during their migrations. Conditions such as mild winters and adequate spring moisture can lead to a healthy bloom of flowering plants, supporting larger moth populations by providing necessary sustenance.
The Moth Life Cycle and Seasonal Swarms
The life cycle of the Miller Moth, a type of army cutworm, plays a significant role in the seasonal swarms observed in Colorado. Their life cycle includes four stages: egg, larva (caterpillar), pupa, and adult moth. Eggs are laid in late summer and early fall, often in weedy areas or fields, and hatch within a few weeks into larvae.
These caterpillars overwinter, feeding on plants like winter wheat and alfalfa as temperatures allow. By mid-spring, the caterpillars are fully grown and burrow into the soil to pupate, a stage that lasts approximately three to six weeks. The adult Miller Moths emerge from pupae between May and June, triggering their annual migration. They fly westward from the plains towards the cooler, higher elevations of the Rocky Mountains, seeking nectar from alpine flowers. A return migration to the plains occurs in the fall for egg-laying, though it is often less noticeable.
Why Moths Seek Shelter Indoors
The appearance of numerous moths inside homes is a common experience during their migratory periods. These moths often seek shelter indoors from various environmental factors. During daylight hours, Miller Moths avoid bright light and prefer dark, tight spaces to rest. Cracks and small openings around doorways, windows, and even in cars provide ideal hiding spots for them.
Moths are also attracted to artificial lights at night, which can draw them towards homes and buildings. While their presence indoors can be inconvenient, these moths do not breed or lay eggs inside homes and typically die within a few days when confined.