Saponins and bio-surfactants
Tea saponin, quillaja, yucca and bio-surfactants share a mechanism: they are amphiphilic molecules that disrupt membranes and improve wetting.
The shared chemistry
Saponins are glycosides in which a hydrophobic aglycone — usually a triterpene or steroid — carries hydrophilic sugar chains. That amphiphilicity produces the foaming that gives them their name and two useful properties: they complex with membrane sterols, disrupting membranes, and they reduce surface tension, improving spray coverage and soil wetting.
Bio-surfactants such as rhamnolipids and glycolipids are microbially produced amphiphiles with similar surface activity and, generally, milder biological effects. They appear on the cosmetic side of the business too, where glycolipids serve as gentle surfactants.
The ones in the range
Tea saponin from Camellia oleifera in Slug Control — see its own page.
Proprietary saponins with bio-surfactants in Jumping Worm Control, alongside geraniol. Here the mechanism is well matched to the target: jumping worms rely on a protective mucus layer, and saponins strip it, driving the worms to the surface where they can be removed. The page for that product should describe this rather than leaving the actives as "proprietary", which is currently the case.
Quillaja saponins from soapbark and yucca extract are the other saponins commonly used in this space, though not currently named in the Vegalab range.
Why saponins matter beyond direct activity
Two secondary roles are easy to overlook. As adjuvants they improve the performance of whatever they are formulated with, by increasing wetting and retention on waxy leaf surfaces and improving soil infiltration — so a saponin in a mixed product may be contributing more through delivery than through direct toxicity. And their surfactancy can improve the distribution of contact actives like geraniol, which matters given how strongly geraniol depends on physical contact.
Is saponins and bio-surfactants safe?
The aquatic hazard is the dominant consideration for all saponins: they are potently toxic to fish through haemolytic action on gill membranes. Mucous-membrane irritation is the main applicator concern. Non-target soft-bodied soil organisms in the treated zone can be affected.