“Ranger, There's a Bug in My Tidepool!”
By Terry Morse
While tidepooling, you might see little blue-black “bugs” swimming in the pools. These are seashore springtails (Anurida maritima), a species of collembolan. Once labeled primitive wingless insects, collembolans are now considered to be close relatives of the true insects.
Seashore springtails, 1/8 inch (3 mm) long, may be found on beach litter between high and low tide levels, under rocks, or moving about on the surface layer in tidepools, where they suck the juices of decaying plants, and perhaps also animals. When the tide is in, seashore springtails shelter in air pockets in rock crevices. While swimming, they are surrounded by a bubble of air held in place by hairs on their cuticle (“skin”), which allows them to breathe.
Another collembolan you may be familiar with is “snow fleas,” tiny dark-bodied springtails that speckle snowy surfaces on warm winter days, leaping about like animated pepper. Snow fleas eat algae and fungus spores on the snow. Seashore springtails and snow fleas are not closely related to true fleas, which are insects, and they don't bite like fleas.
Neither are seashore springtails closely related to the “beach fleas” or “beach hoppers,” scavengers you may see jumping around on seaweeds washed up on beaches. These are shrimp-like amphipod crustaceans.
Springtails have a forked appendage on the underside of the fourth segment of their abdomen, the furcula, which is held cocked by a clasp on the underside of the third segment. Springtails leap by suddenly extending the furcula, which strikes the ground, propelling the animal into the air. The furcula is either reduced or absent in seashore springtails (sources disagree on this). Beach fleas leap by suddenly straightening the bent rear of their abdomen.
For a color photo of a congregation of seashore springtails, see plate 79 in the National Audubon Society Field Guide to North American Insects and Spiders.
Arnett, Ross. 1993. American Insects. Gainesville, FL: Sandhill Crane Press.
Berrill, N.J., and Jacquelyn Berrill. 1957. 1001 Questions Answered About the Seashore. NY: Dover.
Milne, L. and M. Milne. 1980. National Audubon Society Field Guide to North American Insects and Spiders. NY: Knopf.
Ricketts, Edward F., Jack Calvin, and Joel W. Hedgpeth. 1985. Between Pacific Tides, 5th ed. Stanford, CA: Stanford University Press.
Originally published in the May 1998 Sandpiper.
Note added 2 January 2004: Having now had six years of experience looking closely at tidepools at Yaquina Head on the central Oregon coast, USA, that incident in 1998 is the only time I have actually seen a congregation of seashore springtails swimming in a tidepool. Another ranger had seen them that year as well, but I haven’t heard any other reports since then. It’s a bit of a mystery. Perhaps if I spent more time turning over rocks I would find them, but we try not to disturb our intertidal zone because it receives such heavy visitation (tens of thousands of people a year).
Revised 19 May 2004