Pam (Gardengal) posted this a week or so ago, but I suppose we'll have to listen to the "broad spectrum" speech all over again. ;o)

From Extoxnet:
"Effects on Other Animals (Nontarget species): Azadirachtin is relatively harmless to spiders, butterflies, and insects such as bees that pollinate crops and trees, ladybugs that consume aphids, and wasps that act as parasites on various crop pests. This is because neem products must be ingested to be effective. Thus, insects that feed on plant tissue succumb, while those that feed on nectar or other insects rarely contact significant concentrations of neem products. Another study found that only after repeated spraying of highly concentrated neem products onto plants in flower were worker bees at all affected. Under these extreme conditions, the workers carried contaminated pollen or nectar to the hives and fed it to the brood. Small hives then showed insect-growth-regulating effects; however, medium-sized and large bee populations were unaffected (234). A study of neem products and their effect on mortality, growth and reproduction of earthworms in soils was conducted. Positive effects on weight and survival were found in soil treated with ground neem leaves and ground seed kernels under greenhouse conditions. Reproduction was slightly favored over a period of 13 weeks in a neem-enriched substrate in rearing cages. Various neem products were incorporated in the upper 10-cm soil layer of tomato plots. None of the materials had negative side effects on seven species of earthworms (240). No significant effects on other wildlife were reported (238)."

Al

This is in the link below, "Most commercially available neem products list azadirachtin as the primary active ingredient. Such products are broad-spectrum insecticides, which work by contact or ingestion. As an insect growth regulator, azadirachtin prevents insects from molting by inhibiting production of ecdysone, an insect hormone. Azadirachtin is chemically similar to ecdysonlids, the hormones responsible for triggering molts (Weinzierl and Henn 1991). As an anti-feedant it may cause an insect to stop feeding after ingestion due to secondary physiological effects. As an egg-laying deterrent, volatile compounds from neem may repel some insects from depositing eggs on a plant surface." from Cornell University.
Note that it does state in there that these products are "broad-spectrum insecticides".
This product should not, when applied according to directions, have any adverse impact on soil dwelling critters such as earthworms. However, like any other broad spectrum poison if it is applied to the soil it could advresly impact earthworms.

Here is a link that might be useful: About Neem

OK, let's put some common sesne into the definition of the phrase 'broad spectrum'. It *is* broad spectrum in that it messes up insects that ingest it. It may also harm insects sprayed directly with it due to it's oily nature. Some products with neem also contain insecticidal soaps. These would be more toxic than pure neem to insects directly sprayed.

So, if we avoid directly spraying insects and let the plant eating insects poison themselves by eating it as they eat our plants, is it really broad spectrum as something like Sevin is?

It will injure/kill most any insect that eats it as well as some that are directly sprayed with it.

It will not harm non plant eating insects that land on a sprayed plant.

For the OP, according to the studies done, it's harmless on earthworms.

The chances that the Neem had anything to do with the demise of those few earthworms is next to nil, and it's benefits far outweigh any potential negative effect.
Dig through your soil, and i will be willing to bet the farm that you still have active earthworms working there if you have good organic matter content.
In a perfect world with a perfect gardening ecosystem, we would never have to use any insect controls, but this is not a perfect world, and a vegetable garden is not a perfect ecosystem. The time always comes when you have to decide if your want to lose a crop and/or eat bugs, or use an organic control that does minimal damage to deal with infestations. That is the difference between fanatical organics and common-sense organics.

Ron
The Garden Guy
http://www.TheGardenGuy.org
Informative articles, ongoing garden journal and
interactibe message boards.