Harvestmen, commonly known as daddy long-legs, are arachnids often mistaken for spiders. Phalangium opilio is a widespread species within the harvestman order, Opiliones. While sharing some characteristics with spiders, it possesses distinct features that set it apart. Understanding these differences helps in accurate identification.
What Phalangium Opilio Looks Like
Phalangium opilio has a small, oval-shaped body, 3.5 to 9 millimeters long, with males often smaller than females. A key characteristic of harvestmen is their cephalothorax and abdomen are broadly joined, appearing as a single, fused unit. This contrasts with spiders, which have two clearly separated body segments joined by a narrow stalk.
This harvestman has eight long, slender legs; six are primarily used for walking, with the second pair often serving as sensory appendages. Their legs are covered with spines and have multiple pseudosegments, called tarsomeres, at their tips, allowing for flexible movement and climbing. Phalangium opilio typically has one pair of eyes located on a raised tubercle, unlike most spiders that commonly have four or more pairs of eyes. Harvestmen also lack fangs for injecting venom and do not produce silk or spinnerets, unlike spiders.
Natural Environment and Diet
Phalangium opilio is native to Europe and widespread across the Holarctic region. It has also been introduced and established in North America, North Africa, and New Zealand. This species thrives in various open habitats, including meadows, forests, and bogs. It is also found in human-modified environments such as agricultural fields, gardens, urban green spaces, and sometimes within basements or cellars.
This harvestman is a generalist predator and scavenger with an omnivorous diet. It feeds on small, soft-bodied arthropods, including aphids, caterpillars, leafhoppers, beetle larvae, and mites. Phalangium opilio also scavenges on dead insects, decaying organic matter, plant material, and fungi. Its varied diet allows it to persist in diverse environments, contributing to local ecosystems.
Behavior and Life Cycle
Phalangium opilio employs specific defense mechanisms when threatened. It can secrete a foul-smelling fluid to deter predators. Another defense is leg autotomy, where it can detach a leg that continues to twitch, distracting a predator while the harvestman escapes. This ability allows it to survive encounters that might otherwise be fatal.
A common misconception is that harvestmen possess potent venom. However, Phalangium opilio lacks venom glands and fangs, making it harmless to humans.
Its life cycle involves mating, after which the female uses a tube-like ovipositor to lay clusters of eggs, often ranging from ten to several hundred. These eggs are deposited in moist environments, such as under rocks, in soil cracks, or beneath bark. Eggs hatch in three weeks to several months depending on temperature, and the young undergo multiple molts to reach maturity in two to three months. In Europe, Phalangium opilio completes one generation per year, overwintering as eggs, while in parts of North America, two or more generations may occur annually.