ak Woodland Invertebrates O The Little Things Count Richard Little, Ted J. Swiecki, and William Tietje University of California Agriculture and Natural Resources Publication 21598 The printing of this publication was funded in part by the Renewable Extension Act—USDA. The authors wish to acknowledge the Integrated Hardwood Range Management Program, University of California, Berkeley, for its support in the development of this publication. Credits: Jack Kelly Clark: inset p. 3, background pp. 4, 7, 8, 9, 10, inset bottom right p. 8; Ron Mumme: inset top left on cover, inset p. 11; Richard Little: inset bottom left on cover, inset top left p. 8; Edward Ross: inset right center on cover, inset p. 4, inset p. 5, inset p. 9, inset p. 10, inset p. 12; Ted Swiecki: background on cover and pp. i, 1, inset top right p. 8, inset bottom left p. 8. 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Inquiries regarding the University’s equal employment opportunity policies may be directed to: Affirmative Action Contact and Title IX Officer, University of California, Agriculture and Natural Resources, 2801 Second Street, Davis, CA 95618, (530) 750-1397. Email: [email protected]. Website: http://ucanr.edu/sites/anrstaff/Diversity/ Affirmative_Action/. WEB-10/18-GM/CR/WS This publication has been anonymously peer reviewed for technical accuracy by University of California scientists and other qualified professionals. This review process was managed by the ANR Associate Editor for Agronomy and Range Science. ak Woodland Invertebrates O The Little Things Count Richard Little Agriculture Inspector, Biologist, and Staff Entomologist San Luis Obispo County, California Ted J. Swiecki Plant Pathologist Phytosphere Research Vacaville, California William Tietje Natural Resource Specialist Integrated Hardwood and Range Management Program Department of Environmental Science, Policy, and Management University of California, Berkeley University of California Cooperative Extension, San Luis Obispo County Contents Zooming in on a Hidden World ...................... 2 Filbert Weevils and Filbert Worms .............. 2 Oaks for Dinner .................................. 3 Who Is Eating Whom? Oak Enemies’ Natural Enemies.... 4 Tarantula Hawk Wasps....................... 5 California Oak Worm ........................ 6 Human Impacts: Usually More Harm Than Good ........ 6 Oak Galls ................................. 8 What’s in the Soil? Invertebrates Down Below .......... 10 The Big Picture.................................. 11 Bibliography.................................... 13 “When we try to pick out anything by itself, we find it hitched to everything else in the universe.” his well-known quote from the pioneering con- Tservationist John Muir serves as both a starting point and a framework for our exploration of a largely unnoticed universe. This universe exists within one of California’s most important and environmentally impact- ed ecosystems: the oak woodlands. The universe we explore here is the realm of the invertebrates, minute animals whose lives are “hitched” to almost every part of the oak woodland ecosystem. 2 Filbert Weevils Zooming in on a and Filbert Hidden World Worms hether you are collecting alifornia oaks (Quercus spp.) are the dominant tree spe- Wacorns for eating, as Ccies in the coastal ranges and the foothills surrounding California’s Native American pop- ulation did, or for planting, the Central Valley. Oak trees cover about 10 million acres, wormy acorns can be a problem. roughly 10 percent of California’s land area. Many woodlands Insect larvae can destroy much of in California include several different types of oaks. More than an acorn’s insides and may intro- duce fungi and bacteria that will 25 oak species, natural hybrids and varieties, are native to decay what is not eaten. A large California, and nine of these occur only in California. Some percentage of the acorn crop from a given tree may be destroyed by oak woodlands contain other native trees, including gray pine these insects, but damage levels (Pinus sabiniana) and California buckeye (Aesculus californica), can vary widely from tree to tree and year to year. Although acorn and a variety of shrub species. The ground below the oaks is feeders do not harm mature typically carpeted with non-native grasses introduced from the oak trees, they can reduce oak Mediterranean region. However, native bunch grasses and a regeneration. The two different types of variety of forbs occur in many woodlands, and springtime dis- insect larvae that are responsible plays of native wildflowers often brighten the understory. for most wormy acorns are the fil- bert worm (Cydia latiferreana) and Oak woodlands teem with a wide variety of animal filbert weevil (Curculio spp.) lar- life. Over 300 species of vertebrates (animals with backbones) vae. Although both types of larvae are whitish, they can be distin- use California’s oak woodlands, including 170 bird species, 80 guished in several ways. The fil- mammal species, and 60 species of amphibians and reptiles. bert worm is the larva, or caterpil- Although oak trees provide valuable habitat elements (nesting lar, of a brownish, nondescript moth. Filbert worm larvae are rel- sites, cover, thermal protection, food) for many different ver- atively active and have true legs. tebrates, relatively few species make direct use of oaks as a When disturbed, a filbert worm food source. For example, less than 20 percent of the bird and larva may drop down on a silk strand as a spider does. mammal species in oak woodlands eat acorns, and the per- Larvae of the filbert weevil do centage of mammals that browse directly on oak leaves, twigs, not make silk. They are legless, relatively inactive, and tend to and roots is even smaller. But the myriad of invertebrates in curl up in a C shape. Filbert wee- oak woodlands converts the sunlight, carbon dioxide, and vil adults are brown beetles with mineral nutrients absorbed by oak trees into food for many extremely long, thin snouts. Typically, only a single filbert birds, reptiles, amphibians, and mammals. worm larva is found in an acorn, When we look closely at individual oak trees, we but up to eight filbert weevil lar- vae can be found in one acorn. begin to glimpse the universe of the invertebrates. They 3 Insect-infested acorns typi- buzz and drift through the air; climb along and tunnel cally fall earlier than intact through oak leaves, stems, and roots; dig through the soil; acorns. This observation may and swim in watercourses and seasonal ponds. Inver-tebrate have led to the Native American practice of burning the oak organisms vastly outnumber their vertebrate counterparts in understory to control these pests. the oak woodlands: 10 to 100 million individual inverte- Properly-timed burning would destroy wormy acorns from the brates may be present within a single acre of oak current season and reduce pest woodland. populations in the following Invertebrates lack not only backbones, as their name year. Present-day acorn planters implies, they have no internal skeleton at all. This lack of generally use