“Float like a butterfly, sting like a bee,” was Muhammad Ali’s catchphrase, but it turns out a butterfly can pack quite a sting. At least that’s what one non-profit has learned while trying to build affordable housing for seniors on Staten Island. The Metropolitan Council on Jewish Poverty, along with the St. Francis de Sales Development Corp., is trying to build more than 500 units offering assisted living on a vacant lot next to Sea View Hospital. But it has run into headaches because of a local environmentalist group, Protectors of Pine Oak Woods, looking to protect a rare butterfly: the arogos skipper.

While we have nothing against the arogos skipper ourselves, there’s just one complication: The butterfly has been a no show for the past two years. The executive director of the Met Council, William Rapfogel, tells us that his group has had to spend thousands of dollars to hire a butterfly expert. Over the past two summers, the expert has found not a trace of the creatures. So have years of legal wrangling — the Protectors have sued the city to slow the project down and have forced an environmental impact statement — been for naught? Perhaps not. The Protectors claim that the butterflies are supported by ecologically sensitive serpentine rocks that would be disturbed by the construction.

So, add the arogos skipper butterfly to the northern spotted owl and the kangaroo rat on the list of marginal species that have impeded human development. Staten Island has a burgeoning population of seniors, thousands of which civic leaders say have been squeezed off the island. “There is a tremendous need for senior housing,” Mr. Rapfogel told us. “We have no profit motive.” And, as Mr. Rapfogel said, these are Staten Island residents who have devoted their lives to hard work and raising their children. If housing can be built to accommodate a pleasant retirement for these people, then there’s no reason why some butterflies should be allowed to disturb their habitat.

And they probably won’t. The Met Council expects to file its environmental impact statement in May, and the project should be able to get off the ground after that. But before a single unit has been started, Mr. Rapfogel estimates his group has already spent half a million dollars. People complain that it is the free market to blame for a lack of affordable housing. But it has been the so-called conservationists, since at least the early-1990s, that have been lobbying to prevent any development on the land in question. Perhaps people could pay closer attention to the antics of the environmental movement. They sting.