Re: Why are garlic, bay leaf and peppermint effective ant repellants?

Wow!  What a hard question!  I found a gazillion sites listing garlic and mint 
as home remedies for ant problems, but almost nothing on WHY garlic, or other 
plants, repel ants.  Here is some of the information I found, and I hope you 
find it helpful.

Most plants produce defensive chemicals that help fend off insects and diseases. 
These chemicals may be insect poisons, make insects stop eating, or kill fungi.

Destructive insects often locate their food by smell. Many plants, especially 
herbs, produce strong scents which may confuse insect pests looking for 
something to feed on. Garden vegetable plants such as garlic, onions, chives, 
and herbs such as catnip, horehound, wormwood, basil, tansy, and mints all 
produce scents which seem to repel insects or mask the scents which attract 
insects.
(http://www.cce.cornell.edu/suffolk/grownet/organic/complant.htm)
 
Garlic contains many chemical compunds including "allicin" which makes the 
garlic smell, and "ajoenes" which can kill fungus (maybe the 
ants know garlic will kill their main food source, fungi).
(http://www3.mistral.co.uk/garlic/chemicals.htm)

Spearmint also contains many chemicals including carvone which sometimes causes 
an allergic reaction. 
Also present are other chemicals like Phellandrine, Limonene, and Dihydrocarveol 
acetate, acetic, butyric and caproic or caprylic acids.  These strong 
smelling compounds may be disgusting to ants, and spearmint is known to have 
kill insects. 
(http://www.cis.um.edu.mt/~phcy/symp/lilibarb.htm)

I don't know about bayleaves, but presumably they also repel moths.


More home remedies for ants:
http://chppm-www.apgea.army.mil/ento/mythconc.htm#ants

See also : "Plants that repel"
http://www.gifted-gardener.com/giftedgardener/planthatrep.html