Package[fetch_description] does not have a path

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I failed to load URDF file in Gazebo. The model starts to update in a crazy way and then settled for a while.

My launch file is like following:

<launch>
<param name="robot_description" textfile="$(find fetch_robot_des)/urdf/fetch.urdf" />
<include file="$(find gazebo_ros)/launch/empty_world.launch">
</include>
<node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-param robot_description -urdf -model fetch" />
</launch>

And the URDF file is like following:

<robot name="fetch">
  <link name="base_link">
    <inertial>
      <origin rpy="0 0 0" xyz="-0.0036 0.0 0.0014" />
      <mass value="70.1294" />
      <inertia ixx="1.225" ixy="0.0099" ixz="0.0062" iyy="1.2853" iyz="-0.0034" izz="0.987" />
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <geometry>
        <mesh filename="package://fetch_description/meshes/base_link.dae" />
      </geometry>
      <material name="">
        <color rgba="0.356 0.361 0.376 1" />
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <geometry>
        <mesh filename="package://fetch_description/meshes/base_link_collision.STL" />
      </geometry>
    </collision>
  </link>
  <link name="r_wheel_link">
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <mass value="4.3542" />
      <inertia ixx="0.0045" ixy="0" ixz="0" iyy="0.005" iyz="0" izz="0.0045" />
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <geometry>
        <mesh filename="package://fetch_description/meshes/r_wheel_link.STL" />
      </geometry>
      <material name="">
        <color rgba="0.086 0.506 0.767 1" />
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <geometry>
        <mesh filename="package://fetch_description/meshes/r_wheel_link_collision.STL" />
      </geometry>
    </collision>
  </link>
  <joint name="r_wheel_joint" type="continuous">
    <origin rpy="-6.123E-17 0 0" xyz="0.0012914 -0.18738 0.055325" />
    <parent link="base_link" />
    <child link="r_wheel_link" />
    <axis xyz="0 1 0" />
  <limit effort="8.85" velocity="17.4" /></joint>
  <link name="l_wheel_link">
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <mass value="4.3542" />
      <inertia ixx="0.0045" ixy="0" ixz="0" iyy="0.005" iyz="0" izz="0.0045" />
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <geometry>
        <mesh filename="package://fetch_description/meshes/l_wheel_link.STL" />
      </geometry>
      <material name="">
        <color rgba="0.086 0.506 0.767 1" />
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0" />
      <geometry>
        <mesh filename="package://fetch_description/meshes/l_wheel_link_collision.STL" />
      </geometry>
    </collision>
  </link>
  <joint name="l_wheel_joint" type="continuous">
    <origin rpy="-6.123E-17 0 0" xyz="0.0012914 0.18738 0.055325" />
    <parent link="base_link" />
    <child link="l_wheel_link" />
    <axis xyz="0 1 0" />
  <limit effort="8.85" velocity="17.4" /></joint>
  <link name="torso_lift_link">
    <inertial>
      <origin rpy="0 0 0" xyz="-0.0013 -0.0009 0.2935" />
      <mass ...