Millipedes are long, multi-legged arthropods often discovered beneath garden mulch or stones. They are frequently mistaken for pests due to their appearance and tendency to appear in large numbers. The short answer to their role in a garden is that they are overwhelmingly beneficial decomposers, acting as nature’s recyclers. Millipedes primarily feed on decaying plant matter, which makes them allies in maintaining healthy soil ecosystems. However, under specific conditions, these helpful creatures can shift their diet and become problematic.
The Essential Role of Millipedes in Soil Health
Millipedes are classified as detritivores, meaning their diet consists mainly of dead organic material like fallen leaves, wood chips, and other decomposing plant debris. They play a role in breaking down this coarse material into smaller fragments, a process known as fragmentation. This initial breakdown increases the surface area of the organic matter, making it more accessible for bacteria and fungi to complete the decomposition process.
Their feeding and excretion activities are integral to nutrient cycling, particularly the release of elements like nitrogen and phosphorus back into the soil. Soil occupied by millipedes often contains a higher quantity of available nutrients, which directly supports plant growth. As they move and burrow through the soil in search of food, millipedes create small tunnels and pores. This movement helps to aerate the soil, improving water penetration and circulation beneficial for root development.
Identification: Telling Millipedes Apart from Centipedes
Millipedes are often confused with centipedes, which are predators and do not contribute to decomposition. A key visual difference lies in their legs: millipedes have two pairs of legs attached to almost every visible body segment, giving them a dense, multi-legged appearance. Their legs are positioned directly beneath their rounded, cylindrical bodies, and they move slowly with a distinct, wave-like motion.
Centipedes, by contrast, have only one pair of legs per body segment, and their bodies tend to be flatter. Centipede legs stick out to the sides, enabling them to move much more quickly and often scurrying away when disturbed. When threatened, a millipede’s primary defense is to coil its body into a tight spiral or ball, sometimes releasing a foul-smelling secretion. Centipedes are carnivorous and are more likely to attempt to bite or flee quickly.
Conditions That Lead to Plant Damage
Millipedes are not inclined to eat healthy, living plant material, preferring the softer texture of decaying matter. However, this preference can change when environmental conditions become stressful, causing them to seek alternative food and moisture sources. One common trigger is a high population density combined with a scarcity of their preferred organic food, such as in gardens kept excessively tidy of leaf litter and mulch.
Millipedes require a damp environment to survive and are highly susceptible to drying out. During periods of hot, dry weather, or when the soil in their habitat dries out, they may turn to living plants to obtain necessary moisture. This opportunistic feeding typically targets tender tissues, such as young seedlings, soft fruits resting on the ground, or roots that are already damaged.
Managing Millipede Populations in Gardens
If millipedes begin to cause noticeable damage, management strategies focus on modifying the conditions that encouraged their population surge or behavior change. Since they thrive in moisture and decaying material, reducing excessive surface water and organic debris around plant bases can help. Watering plants in the morning allows the soil surface to dry out before the millipedes become most active at night.
Thinning out thick layers of mulch to no more than two to four inches and improving air circulation reduces the overly damp conditions they seek. For direct control, simple traps can be effective; millipedes will crawl into hollowed-out potatoes or melons placed cut-side down overnight, allowing for easy removal the following morning. Physical barriers, such as a band of diatomaceous earth, can also be applied around vulnerable plants or garden beds, as this abrasive powder causes dehydration in the arthropods.