EPOW - Ecology Picture of the Week

Explanation:   Barely able to cover Lincoln's nose on a U.S. penny, these adult spiders are micryphantids ... some of the world's smallest spiders.  Yet these tiny creatures are amazingly abundant in their forest habitats, and may provide essential functions for keeping forests healthy.

These specimens were captured in the high Cascade Mountains of southern Washington state, U.S., northeast of Mt. St. Helens.  Just sorting and counting the several hundred micryphantid specimens from our pitfall traps and beat-and-sweep sampling was a task.  

Micryphantid spider specimens stored in a tiny well plate cell.  Some, perhaps many, of these spiders remain unknown to science and await naming and life history studies.

Micryphantid spiders, also called dwarf spiders or microspiders, constitute a very large species group.  Most dwarf spiders are less than 2 mm (0.08 inches) in length.  They usually occur on the ground in leaf litter and decaying wood, and likely provide valuable ecological functions of predation on other microarthropods and tiny insects, keeping their populations in check.  Some dwarf spiders might serve the valuable function of keeping pest insects in check in agricultural fields, including rice paddy fields, thus aiding the farmer.

Micryphantid spiders can reach densities of up to 150 individuals per square meter of forest soil, and are common in mature and young forests alike.

Despite their abundance and ubiquitous occurrence in most  forests, they are greatly understudied and seldom even seen except by careful collectors.  They truly constitute what has been called "furtive" or hidden biodiversity -- organisms that may play valuable and essential ecologial roles in their ecosystems (including in soils) but which are all but unknown and unseen.

Acknowledgments:
   Many thanks to Jeffrey Ricklefs for overseeing the field crew that collected these, and hundreds of other, invertebrate specimens for my Old Forest Remnants Study; and to entomologist Andy Moldenke for identifying the specimens.  

Information:  
     Mansour, F., and U. Heimbach. 1993. Evaluation of lycosid, micryphantid and linyphiid spiders as predators of Rhopalosiphum padi (Hom.: Aphididae) and their functional response to prey density —laboratory experiments. Entomophaga 38:79-87.
     Sunderland, K. 1999. Mechanisms underlying the effects of spiders on pest populations. The Journal of Arachnology 27:308-316.