Snail Tale

https://www.inaturalist.org/observations/14020490

Snails estivate. If you want to watch them do it, late summer is a good time. Just head over to either of the two entrances to Mission Trails Regional Park located on Calle de Vida in Tierrasanta. At this time of year, the dry vegetation teems with the inactivity of estivating snails. Estivation, sometimes called summer sleep, is an adaptation that allows the snail to survive the hot dry summers of a Mediterranean climate until winter rains stimulate it to resume feeding, sliming and reproducing.


White garden snails (Theba pisana) invaded the park a couple of decades ago. Unlike most other snails, these Sicilian natives prefer to estivate high up. In MTRP they climb stalks of similarly non-native mustard, grasses, and thistles, but they also cling to Yerba Santa, Laurel Sumac, Chamise, California Sagebrush and other natives. On one visit to MTRP, I tired of counting snails, but estimated that there were over 500 on one sagebrush plant, and all around me the scene was repeated. Elsewhere, others have reported over 3,000 snails on one tree. The white garden snail is an agricultural pest, known to damage vegetable and fruit crops (especially citrus) and ornamental plants by feeding on foliage and leaving a thick slime trail that can inhibit pollination and lower the quality of harvested produce. At this time of year, even the native plants look stressed, so it is hard to determine if the snails are damaging them.

You can enliven your observations of Theba pisana by bringing along a water spray bottle. A few spritzes, and like magic, the snails come to life, albeit at a snail’s pace. I read that it would take 15 minutes or so. My snails were slower than that—30 minutes after I spritzed them, most were moving around and began to feed on the lettuce I provided. (I placed a stalk with 20 or so clinging snails in a terrarium for this experiment.) True to form, after feeding, the snails migrated to the lid of the terrarium, the highest point in their now-limited world of plastic.

I sprayed the clinging snails frequently to deter them from secreting mucus and affixing themselves to the terrarium. The mucus dries to a hard wall called an epiphragm that protects the snail from desiccation during dry periods. (An “epiphragm” or covering wall can be compared to a “diaphragm” or dividing wall such as the muscle that divides our chest and abdominal cavities.)

A white garden snail can be distinguished from the common brown garden snail (Cornu aspersum) by its whitish color, smaller size of adult snails, and the lack of a flange or ridge along the shell opening. As noted above, the white garden snail is likely to climb up structures to estivate, while the brown garden snail seeks out sheltered areas such as under logs or rocks. Milk snails (Otala lactea) are white with brown bands, are larger, do not frequent arid environments, and have a flange at the shell opening. Milk snails were introduced from Europe and are edible.

Like all snails, white garden snails are hermaphrodites. Each snail lays about 120 eggs at a time in the ground after winter rains begin. Hatching occurs after 20 days and the snails live an average of 2 to 3 years.

San Diego County has earned the distinction of being the only place in the United States where the white garden snail is established. Los Angeles County has reported the snail, but claims to have eradicated it. San Diego officials have also tried to eradicate the snail. In the early part of the 20th century, when the snail was first discovered in La Jolla, teams went out with hoes and axes to clear entire canyons of vegetation, followed by a crew that sprayed a petroleum mist that they then ignited. This scorched earth strategy was apparently successful in eliminating the snails from La Jolla for a time. In 2003, the Cedar Fire burned the vegetation along Calle de Vida, temporarily eradicating the snail from MTRP. But they are back and appear to be thriving. Take a walk along Calle de Vida. You can’t miss them. They are everywhere you look, estivating right in front of your eyes.

Publicado por milliebasden milliebasden, 22 de julio de 2020

Comentarios

Thank you, Millie!

Publicado por klyle161 hace alrededor de 1 año (Marca)

Very nice.

Publicado por bmcneece hace alrededor de 1 año (Marca)

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