It really should say "Search Engines" but it's not difficult, simply edit the "island_whos_online.tpl" file either from the template editor in the CP or in notepad on your computer (be sure to re-upload the file).
You're looking to remove this:
{$spiders}
{if $spiders == 1}
<?php echo $ubbt_lang['ONLINE_SPIDER']?>
{else}
<?php echo $ubbt_lang['ONLINE_SPIDERS']?>
{/if}
