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Bug of the Month: Daddy longlegs

Common name: Daddy longlegs (a name for all the Opiliones)

Latin name: Phalangium opilio

Taxonomy:
Kingdom Animalia
   Phylum Arthropoda
      Class Arachnida
         Order Opiliones
            Family Phalangiidae

Daddy longlegs in general

Daddy longlegs, or harvestmen, resemble their close arachnid relatives the spiders and mites in having four pairs of legs, a two-part body, simple eyes, and no antennae. Daddy longlegs are most often confused with spiders, but can be easily distinguished from them by body shape: in spiders the two body segments (abdomen and cephalothorax) are separated by a constricted “waist,” while in daddy longlegs, the two segments are broadly joined so that they look like one oval body part. Also, daddy longlegs have just two eyes (spiders have 6 to 8), and they do not produce silk. Most daddy longlegs live in damp, dark places and are nocturnal predators and scavengers.

Contrary to popular belief, daddy longlegs do not have venom glands like spiders, so they cannot give you a painful, poisonous bite (see web link below). For defense, daddy longlegs have foul-smelling scent glands, and legs that break off easily (and continue to twitch) in a predator’s grasp. There are about 6000 described species of daddy longlegs around the world, and the majority live in the tropics.

How to identify Phalangium opilio

The body is soft and leathery-looking, about ¼ inch long (slightly larger for females), and is light-colored underneath, with a darker brown pattern on its back. The long legs are usually pale or brown. The males are very distinctive because they have large horns on the last segment of the “chelicerae” (see photo).  Females do not have the horns, but have the same general body plan. Other characteristics that separate this species from other similar-looking daddy longlegs on the islands are too small to see with the naked eye.

overhead view of a daddy longlegs

Eight legs or ten? If you count all the long appendages coming out from the body, you'll count ten. The front pair of "legs" however, are actually shorter pedipalps, and these function both as sensory organs and to aid in eating food. P. opilio has a claw at the end of each pedipalp.

overhead view of a daddy longlegs body

In daddy longlegs, the two body segments are broadly fused together, so that the body looks like one solid oval (compare this to the two distinct body segments in the woodlouse hunter spider). The one pair of eyes is raised up on a bump.

close up view of underside of Phalangium Opilio

Ventral view of Phalangium opilio. Another way that daddy longlegs differ from spiders is that their abdomens are segmented. You can easily see the segments here; contrast this to the smooth unsegmented abdomen of the woodlouse hunter spider.

Chelicerae are paired fang-like appendages on the head that are used to grasp food; in daddy longlegs they do NOT deliver venom as they do in spiders. This male P. opilio has large horns pointing upwards on the chelicerae.

 

Male Phalangium opilio. You can see the large “horns” in profile, on the chelicerae.

Where to find Phalangium opilio on the Boston Harbor Islands

Because of their long legs, these daddy longlegs can move quickly over the ground, in the grass, on the branches of shrubs, or up tree trunks and walls. They are frequently associated with humans, and often live in or near crop fields, buildings, open woods, and gardens. Phalangium opilio searches for prey mostly at night, so during the day they will be hiding out under rocks, in vegetation, or in other damp, dark places

How Phalangium opilio makes a living

Phlangium opilio was one of the first daddy longleg species to be given a name (by Linnaeus in 1758) and it is probably the most-studied daddy longlegs in the world.  In cooler regions it has one generation per year, and the overwintering stage is the egg. In warmer climates it can have two or three generations, and can overwinter as an egg, nymph, or adult. Females lay their eggs in moist areas in the soil, under rocks or leaves, and in tree bark crevices. P. opilio prey on many kinds of soft-bodied invertebrates, and will even scavenge on dead vertebrates. They can be helpful for gardeners or farmers because they can help control crop pests such as aphids, slugs, and insect larvae.

Where in the world Phalangium opilio occurs

Phalangium opilio ranges through much of Europe, Asia, and North America. It has also been introduced to New Zealand.

To learn more about Phalangium opilio (and daddy longlegs in general)

On the web:

In print:

    Hillyard, P.D. 2005. Harvestmen: keys and notes for the identification of British species. Synopses of the British Fauna (New Series) No. 4. Crothers, J.H. and P.J. Hayward (eds.) FSC Publications. Shrewsbury, England. 167 pages.

    Pinto-da-Rocha, R., G. Machado, and G. Giribet (eds). 2007. Harvestmen: the biology of Opiliones. Harvard University Press. Cambridge, MA. 597 pages.