Exclude posts with featured image from loop

This may seem an odd request but I’m looking for a way to display a list of posts excluding any that have a featured image.

I have a row of four posts which include the most recent four posts with a featured image. I would then like to display all the other posts that DO NOT have a featured image as links underneath.

This is what I’ve come u with so far:

<div class="row">
	<?php
	global $post;
	$args = array( 'numberposts' => 4, 'category' => 10,'meta_key'=>'_thumbnail_id', );
	$myposts = get_posts( $args );
	foreach( $myposts as $post ) :	setup_postdata($post); ?>
		<li class="span2">
		<a href="<?php the_permalink() ?>">
			<div class="featured-blog">
			<?php the_post_thumbnail( 'post' ); ?>
			<h3><?php the_title(); ?></h3>
			<p><?php the_time('d/m/y:') ?> - <?php the_excerpt(); ?></p>
			</div>
		</a>
		</li>
	<?php endforeach; ?>
</div>

<div class="row">
	<div class="span2">
	<h3>Other News</h3>
	</div>

	<div class="span3">
	<?php
	global $post;
	$args = array( 'numberposts' => 4, 'category' => 10 );
	$myposts = get_posts( $args );
	foreach( $myposts as $post ) :	setup_postdata($post); ?>
	<li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
	<?php endforeach; ?>
	</div>

	<div class="span3">
	<?php
	global $post;
	$args = array( 'numberposts' => 4, 'offset' => 4, 'category' => 10 );
	$myposts = get_posts( $args );
	foreach( $myposts as $post ) :	setup_postdata($post); ?>
		<li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
	<?php endforeach; ?>
	</div>
</div>