Big fleas have little fleas upon their backs to bite em,
And little fleas have lesser fleas and so ad infinitum.

 There is a Wikipedia entry about this Nursery Rhyme.

Jonathan Swift wrote these lines in his poem On poetry:-

So, naturalists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite ‘em
And so proceed ad infinitum.

 A flea market is a second-hand clothes outlet.  Maybe the previous owners were not too particular.

A flea circus is performing fleas.  The owners allowed the fleas to feed on them!  It could be called a symbiotic relationship.  The fleas and the owner had their means of livelihood!

I wrote a few limericks recently.  While I was in limerick-mode I also came up with this one:

There was a young man of St. Bees,
Who spent days on end catching fleas;

A circus he had,
But their bites were so bad
He had bumps on his hands and his knees.

A flea in your ear is a telling off.

Nit-picking is a figurative term for criticising details.

As snug as a bug in a rug is an expression meaning cosy.  The bug referred to is presumably a bedbug.  There is a rhyme which I remember as:

Night, night,
Sleep tight
And don’t let the bugs bite.

A worm’s eye view is from ground-level.  Here is a related post.

The worm has turned is a saying about a passive person, who suddenly becomes assertive.

When you were knee-high to a grasshopper…

or the lines of a song when I was small and Christmas trees were tall.

A butterfly kiss is given with the eyelashes.

If you wish to live and thrive let the spider run alive.
Arachnophobia is a common fear.  In Britain we have no poisonous spiders, so there is not much to fear from them.  Spiders keep down the population of harmful insects.  They are fascinating creatures.  Their webs are engineering masterpieces and their silk is very strong.

Making a bee-line means going directly and purposefully to a place or person.  Bees are insects in need of encouragement.  I have mentioned them in my posts A community, How I met a blogger I follow and Buzz, buzz, buzz

Catching crabs is an expression used to tell a novice oarsman that his style of rowing is incorrect.  “You’ll be catching crabs!”  From the bottom of the lake, no doubt.

Creepy-crawlies are insects, their larvae, spiders, woodlice, earwigs, centipedes, millipedes and other small creatures.  The term for them used in the National Curriculum when my children were at school was mini-bugs.

David used the image of a worm in Psalm 22:6 (NIV) But I am a worm and not a man…

This is a prophetic psalm.  Why not click to read it all Psalm 22?

Related posts http://bartwolffe.wordpress.com/2013/08/15/lepidoptera/

http://heathervoid.wordpress.com/2013/08/16/lifespans/

http://ramtopsrac.wordpress.com/2013/08/18/best-butterfly-day-2013-new-forest/