Two environmental groups said they plan to sue the Interior Department to force a decision on whether to protect the monarch butterfly as a “threatened” animal under the Endangered Species Act. The butterfly’s population dropped 80 percent over the past two decades. “It’s important that we protect monarchs now, before it’s too late,” said George Kimbrell of the anti-GMO Center for Food Safety, one of the groups involved. The other is the Center for Biological Diversity. The groups petitioned the government in August 2014 for a listing. “The … lawsuit will force the agency to commit to a legally binding date to issue a final decision on the monarch’s protection,” said the groups, who say widespread planting of GMO crops and related spraying by herbicides “has virtually wiped out milkweed plants,” a prime food for the butterfly. Contributing to the decline are climate change, urban sprawl and logging in the Mexican forests that are the butterfly’s winter habitat.