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Phalangium opilio
(Arachnida: Opiliones, Phalangiidae)
Harvestman, Daddy longlegs, Harvest spider

by Mark Schmaedick, Land Grant Program, American Samoa Community College, Pago Pago, AS

Of the many species of harvestmen known, P. opilio tends to be the most common in relatively disturbed habitats such as most crops in temperate regions. Like the spiders and most adult mites, harvestmen have two major body sections and eight legs and lack antennae. Unlike spiders, the two body sections of harvestmen are broadly joined and no web spinning organs are present. Harvestmen differ from most mites by their larger size and by having the posterior body section distinctly segmented.

Appearance

The most notable features of P. opilio and many other harvestmen are the long, slender legs and short, globular body. Adult body length is approximately 3.5–9 mm, with males generally smaller than females. The upper surface of the body is colored with an indistinct and variable light gray or brown pattern, and the lower surface is typically light cream. Immatures are similar to adults, only smaller and with legs shorter relative to the body size. Eggs are spherical, about 0.4 mm diameter, with a smooth surface and color changing from off-white to dark gray-brown as they mature. They are laid in clusters of around ten to several hundred.

Habitat (Crops)

Harvestmen are often common in crops such as corn, alfalfa, small grains, potatoes, cabbage, strawberries, and apple in most temperate regions of the world.

Pests Attacked

Harvestmen will feed on many soft bodied arthropods in crops, including aphids, caterpillars, leafhoppers, beetle larvae, mites, and small slugs.

Life Cycle

In Europe P. opilio has a single generation per year and overwinters as eggs. In parts of North America two or more generations may occur, and eggs, immatures, or adults may overwinter. Eggs are laid in moist areas under rocks, in cracks in the soil, or between the soil and the crowns or recumbent leaves of plants. The eggs hatch in three weeks to five months or more, depending on temperature, and the immatures undergo several molts and reach maturity in two to three months, again depending on temperature.

Relative Effectiveness

Although P. opilio by itself appears unable to keep populations of any pest under control, it serves as one member of a complex of generalist predators that exist in many crops and that together are able to help keep pest densities low. In addition to pest arthropods, P. opilio also may feed on dead insects and other decaying material, as well as earthworms, other harvestmen, spiders and other beneficial invertebrates. Although its generalist feeding habits and tendency for cannibalism may appear to reduce its value in some situations, they may also allow it to persist in the crop during periods of low pest density and help suppress outbreaks of pests in their early stages.

Pesticide Susceptibility

P. opilio is highly susceptible to at least some broad spectrum insecticides, while some more specific products, such as Bts, appear to be less harmful.

Conservation

Avoid using broad spectrum insecticides as much as possible.

Commercial Availability

Not currently available commercially.

References

Bachmann, E. and M. Schaefer. 1983. Notes on the life cycle of Phalangium opilio (Arachnida: Opilionida). Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg. 26: 255–263.

Bishop, S. C. 1949. The Phalangida (Opiliones) of New York, with special reference to the species of the Edmund Niles Huyck Preserve, Rensselaerville, New York. Rochester Academy of Science. Proceedings 9: 159–235.

Clingenpeel, L. W. and A. L. Edgar. 1966. Certain ecological aspects of Phalangium opilio (Arthropoda: Opiliones). Papers of the Michigan Academy of Science, Arts, and Letters 51: 119–126.

Cokendolpher, J. C. and V. F. Lee. 1993. Catalogue of the Cyphopalpatores and Bibliography of the Harvestmen (Arachnida, Opiliones) of Greenland, Canada, U.S.A., and Mexico. Vintage Press, Lubbock, TX.

Dixon, P. L. and R. G. McKinlay. 1989. Aphid predation by harvestmen in potato fields in Scotland. The Journal of Arachnology 17: 253–255.

Drummond, F., Y. Suhaya, and E. Groden. 1990. Predation on the Colorado potato beetle (Coleoptera: Chrysomelidae) by Phalangium opilio (Opiliones: Phalangidae). Journal of Economic Entomology 83: 772–778.

Edgar, A. L. 1990. Opiliones (Phalangida). Pp. 529–581. In: D. L. Dindal (ed.), Soil Biology Guide. John Wiley & Sons, NY.

Hilliard, P. D. and J. H. P. Sankey. 1989. Harvestmen: Keys and Notes for the Identification of the Species, 2nd ed. E. J. Brill, NY.

Vanuytven, H. 2000. Arachnology, The Study of Arachnids. Opiliones: Harvestmen, Daddy-Longlegs. http://www.arachnology.be/Arachnology.php

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