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Insect and Spider Biodiversity on Marine Corps Base Camp Pendleton

Camp Pendleton, located in north San Diego County, is a 200-square-mile area that serves as the major West Coast base of the United States Marine Corps. Because it is relatively isolated and undeveloped, it retains an incredible amount of biodiversity.

Insects and spiders are critical to ecosystem health, but poorly documented in Southern California natural habitats. Museum researchers are working with Marine Corps staff on Camp Pendleton in order to develop a baseline inventory of the base. Environmental staff on the base hope to repeat the study in future years to monitor the impact of climate change.

To date, our entomologists have been working on the base for four years, studying insects and spiders in six vegetation communities (dune, estuary, coastal sage scrub, riparian woodland, perennial grassland, and chaparral).

Surveying involved various approaches over many months, from setting pitfall traps to study non-flyers like spiders, ants, and beetles, to using pan traps and Malaise traps for flower-visiting insects and pollinators like bees, wasps, flies, and some beetles. Ants were collected by setting out index cards baited with tuna or cookie crumbs, and insects and spiders in decomposing matter were found by gathering leaf litter and sifting it through coarse screens to collect.

The team has made an inventory and is recording ecological functions—like pollinating or decomposing—of each insect and spider type. These data are being used to develop reports and checklists for the different habitats. Meanwhile, the specimens that were collected are housed at the Museum, where they and the information gained from this ongoing study will be a resource for future research in how changes to climate and weather patterns affect the diversity and abundance of insect and spider life on the base.

Ten spider families most common on Camp Pendleton

Wolf spiders (Lycosidae) don’t create webs, but are ground runners that actively stalk prey from under rocks, wood or other debris. The researchers detected five species and found them in every habitat except the dunes. They reported when they walked in riparian habitat, it was not unusual to see dozens scatter in front of them.

Jumping spiders (Salticidae) included 13 species, and they were found in all habitats. The team collected most from grasslands, possibly because it is easier to see them there.

Ground spiders (Gnaphosidae) are ground runners that stalk prey and do not create webs. The entomologist identified thirteen species. These spiders were active year-round and found in all habitats.

Cobweb spiders (Theridiidae) were especially abundant in grasslands and the estuary, but were not found in the dunes. Nine species were detected, including black and brown widows.

Crab spiders (Thomisidae) do not build webs, but sit and wait to ambush prey. These spiders were most active in spring and summer and the eight species found were mostly in grasslands.

Sheetweb weavers (Linyphiidae) build sheet-like webs often with a tubular retreat near the ground or in foliage. The eight species on the base were most active in spring and summer, especially in chaparral.

Funnel Web Weavers (Agelenidae) also build sheet-like webs with a tubular retreat. They are active year round and were most often found in dunes.

Meshweb weavers (Dictynidae) build webs to capture prey in spaces in vegetation, rocks and wood. They were active in spring and summer and especially abundant in riparian habitat.

Sand-swimming spiders (Zodariidae) build tubular webs in dunes under sandy surfaces, “sand swim” under the surface and rarely come above it. They are most active during the hot summer months. The researchers detected only one species of these spiders.

Lynx spiders (Oxyopidae) are stalkers that actively hunt prey on the ground or in foliage with snare webs. They are known to live in chaparral, but, surprisingly, the team found them year-round in all the habitats on the base, except chaparral.

Posted by The Nat on October 8, 2019

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