Burrowing Habits of Earthworms

There are more than 7,000 known species of earthworms across the globe, each with its own distinct physiological makeup and behaviors. While all earthworms are scavengers that burrow through soils and feed on dead organic matter, only some species create complex tunnels and permanent burrow systems. Regardless of whether an earthworm's burrows are permanent or not, this behavior benefits soil conditions and the overall health of local ecosystems.

  1. Types

    • Earthworm species can be separated into three main categories: epigeic, endogeic, and anecic. The first two include horizontal burrowing types of earthworms that tunnel through soil but make only temporary channels. Anecic species, however, create permanent burrow systems deep beneath the soil, sometimes as deep as several meters. One of the most well-known deep-burrowing earthworm species is the Lumbricus terrestris, also known as the night crawler.

    Reasons

    • Epigeic and endogeic earthworms burrow horizontally to move around and find food. Additionally, Anecic earthworm species create burrow systems for protection. Rather than eating as they go, these species pull organic matter from the surface soil into these burrows before eating, which offers them a reprieve from predators or other worms. Deep-burrowing species have even been known to block burrow entrances with organic matter or cast (earthworm excretions) in order to provide further protection.

    Mechanics

    • All earthworms burrow through the soil in much the same way. Because it doesn't have appendages, an earthworm must flex and contract different parts of its body in order to slowly squirm its way through the earth. Each worm does have a layer of tiny bristles, known as setae. Though they don't help with creating burrows, these bristles do help each earthworm move along its burrow system and also anchor it into the burrow if a predator tries to pull it out.

    Benefits

    • Earthworm tunnel systems and burrows that are beneficial to local ecosystems because they help water maintain porosity. Horizontal tunnels near the surface of the soil helps the top layers retain water content, giving plants the water needed to survive. At the same time, the tunnels from deep-burrowing earthworm species drain excess levels of water so that plants don't drown after heavy rains.