Thinopinus pictus, a Predatory Intertidal Staphylinid

If you walk the drift line you’ll want to get to know Thinopinus pictus, the pictured rove beetle. Pictured roves roam the damp sand between the swash and dry sand ambushing beach hoppers. They’re most active at night, but the odds of running across one on your morning walk are high. You’ll have to watch carefully though, because they blend in on damp sand.

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Thinopinus pictus, pictured rove beetle (adult)

Rove beetles, like all coleopterans, are holometabolous. They have complete metamorphosis and the larvae, grubs, like the one shown below, pass through a pupal stage before emerging as adults.

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Thinopinus pictus, pictured rove beetle (grub)

Thinipinus pictus lives on exposed beaches where its dependency on estuarine and subtidal ecosystems isn’t immediately obvious. Once understood, it’s an endearing quality. Specializing on beach hoppers, anything good for Megalorchestia californiana and M. columbiana is good for T. pictus. Juicy hoppers make a living on drift masses of eelgrass from the estuaries, and kelp from the subtidal. The band of damp sand around the drift line is where hoppers are hunted down or ambushed by pictured roves. The system of predator and prey is regulated by the sporadic deposition of drifted macrophytes on the beach. I showed some photos and wrote a few words about beach hoppers and drift kelp in An Ordinary Beach Cast Kelp.

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California beach hopper, Megalorchestia californiana, the prey
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Thinopinus pictus, the predator

When T. pictus isn’t out chasing down Megalorchestia californiana or engaging in other surface activities, which is most of the time, they dedicate themselves to burrows they construct themselves.

 

I took all the photos for this post, except the one of the T. pictus grub, early on July 23, 2016. If you want to see some other the other things I found in the drift line that morning, click here.

References

Craig, P. C. 1970. The Behavior and Distribution of the Intertidal Sand Beetle, Thinopinus Pictus (Coleoptera: Staphylinidae). Ecology, 51: 1012–1017. DOI: 10.2307/1933627

Laura J. Richards. 1982. Foraging behaviour of the intertidal beetle Thinopinus pictus (Staphylinidae). PhD Thesis, The University of British Columbia.

Laura J. Richards. 1983. Feeding and activity patterns of an intertidal beetle. Journal of Experimental Marine Biology and Ecology, 73(3): 213-224. doi:10.1016/0022-0981(83)90048-5

Acknowledgements

Mark Shelton, Associate Dean of the College of Agriculture (Emeritus), Cal Poly, San Luis Obispo, and a Registered Professional Entomologist, kindly confirmed that my photo of adult T. pictus was indeed an adult. He explained that all beetles are holometabolous after I wondered if I had some kind of intermediate nymph on my hands. Most importantly, he helped me feel comfortable calling beetle larvae grubs. I thank him.