NORMALLY, IT IS a mistake to read much into a decision by the Supreme Court not to hear a case. But the court's decision last week not to take up a case called GDF Realty Investments v. Norton is worthy of note. The court sat for a long time on the case, a challenge out of Texas to the application of the Endangered Species Act to insects that live only in a few caves in the Lone Star State. It waited, in fact, until after resolving the recent medical marijuana case, to which GDF Realty is closely related as a legal matter. The decision not to hear it suggests that the justices are not itching to radically redefine the balance of power between Congress and the states. This is good news for those who believe in strong federal environmental protections, the policy area likely to be most devastated by a revolutionary approach to federalism.

Medical marijuana and cave-dwelling insects may not seem to have much in common, but federal authority over both depends on the same constitutional principle: Congress's power to regulate interstate commerce. The court over the past decade has reminded Congress that this power, while broad, is not infinite; a valid exercise of it must have some relationship to commerce. This reminder is healthy, but it also poses dangers, and the court has left key questions unanswered: What about an endangered species that lives only in a single state but is threatened by commercial activity? This is the question posed by GDF Realty and some other cases pending in the lower courts.

All of the courts of appeals that have examined the question have come to the same conclusion: that the Endangered Species Act does, in fact, validly protect species that live only in one state. And while some conservative judges have played key roles in these cases, there has also been a ferocious series of dissents from other conservatives who have made no effort to hide their hostility to environmental values. In GDF Realty, for example, Judge Edith Jones of the U.S. Court of Appeals for the 5th Circuit began a dissent by thundering, "For the sake of species of 1/8-inch-long cave bugs, which lack any known value in commerce, much less interstate commerce, the [court] crafted a constitutionally limitless theory of federal protection." In a similar case in the D.C. Circuit, Judge David B. Sentelle complained that the law was being used to prevent the building of a hospital when "the bugs smashed upon [the] windshields [of its ambulances] might turn out to include the Delhi Sands Flower-Loving Fly or some other species of rare insect."

The high court's decision not to hear GDF Realty leaves open the question of how, in the long run, it will regard protections for those species unfortunate enough to live only in a single state. It does suggest, however, that the justices are not, like Judges Jones and Sentelle, fuming about the supposed assault on states' rights that aggressive federal protections of the environment represent. That alone is good news -- and not just for cave bugs.