Letter to San Diego Native Plant Society--White Snail threat

Dear San Diego Native Plant Society,
I left a phone message today regarding the threat of the white garden snail, Theba pisana, to our native plants here in San Diego County particularly the lupine varieties. This email is to further explain the message.

I am concerned that all our San Diego native plant species are potentially threatened by this snail. Our natives did not co-evolve with snail predation and do not seem to have toxins necessary to discourage the snail from eating them. Our natives legumes (especially the tiny lupines) seem most at threat if the pattern of depredation of Theba pisana in my yard reflect what may be happening in undisturbed areas.

The white snails as tiny newly hatched, pea sized babies climb immediately up to the top of my bush lupines by the hundreds and started stripping leaves. I could not miss a day of hand collecting the tiny, hard-to-see, snails without losing a plant or two. A few other plants were affected as well (Rosa malva). The non-native clover weeds were eaten last. The non-natives seem to have something that discourages the snails a little bit. Whereas the native legumes seemed to be vacuumed down. The snail leaves nothing behind but the thickest stems.

These white snails seem to survive in much drier habitats than the common brown snail. I have seen them estivating by the hundreds on anise stalks in July, where in all my previous twenty years in the area, I had never seen one snail of any kind, at any time. Let alone in mid-summer. It seems it can easily estivate in an open dry field with no extant brown snail population.

It also seems to breed at a voracious rate. This past winter it had an incredibly successful breeding season. It seems to breed several times faster than the brown snail. This rainy season was the first time I have seen the white snails in my yard. Previously I had seen them 1/2 mile a way in a field. Even though they were in the midst of an initial colonization of a yard with a resident brown and collate snail population, they were so successful that I saw thousands of these snails in places where there had in previously been only few dozen brown snails.

I have never had brown snail problems (dry year or wet year) as I have a very healthy population of deccolate snails. Most of the baby browns seem to be eaten on the ground by the decollates, but the baby whites immediately crawl straight up into plants and bushes when they hatch and they stay there day and night. They do not come down to the ground during the day. From hatching and emergence they stay out of reach of the decollates.

I do not know if this concern has been discussed by your group. The county of San Diego pest control officials seem to have given up on efforts to eradicate it. Indeed without biological controls brought from the Mediterrean area, its native habitat, I see no way to control it.

I would think that an alliance of CNPS and California Farm Bureau might convince the California Ag Department to import parasitic wasps as a control for the snail. Apparently these kind of wasps do exist and are being tried in Australia as a control measure.

The white snail could be a huge threat to California's alfalfa crop if the snail makes its way to the San Joaquin Valley where alfalfa is major crop. Many San Joaquin farmers are switching from cotton to alfalfa.

If internet stories of the damage white snail have done to alfalfa crops in Australia are true, there will be a huge hue and cry when the snails reach our alfalfa growing regions. Immediately lots of money will be spent and a solution found to control the snails. But by that time many of our native local belly flowers may be gone (esp the legumes).

Just wanted to make sure that the threat of Theba pisana to our native plants is on the radar