ansible teardown problem

ec2-py.json

#This is the output of running ec2.py
{
  "ec2": [
    "54.201.98.213"
  ],
  "i-8bcae5bf": [
    "54.201.98.213"
  ],
  "key_ansible-1": [
    "54.201.98.213"
  ],
  "security_group_default": [
    "54.201.98.213"
  ],
  "type_t1_micro": [
    "54.201.98.213"
  ],
  "us-west-2": [
    "54.201.98.213"
  ],
  "us-west-2c": [
    "54.201.98.213"
  ]
}

teardown-ansible.yml

# this is my teardown file
---
- name: Teardown up Amazon Instance
  #also tried using "security_group_default" with the "ansible-playbook -i ec2.py" option
  hosts: localhost 
  user: ubuntu
  gather_facts: False
  vars:
  #  ec2: { instance_ids: "{{ instance_ids }}" }
     group_names: security_group_default
  roles:
   - aws
  tasks:
    - name: teardown ec2 instances 
      local_action:
        module: ec2
        keypair: "{{ key_name }}"
        key_name: "{{ key_name }}"
        ec2_access_key: "{{ aws_access_key }}"
        ec2_secret_key: "{{ aws_secret_key }}"
        state: absent
        region: us-west-2
        #group: "default"
        #instance_tags: '{"name":"sss"}'
        instance_ids:  "{{group_names}}"
      tags:
        - teardown