What is this? Spider like creature?

Hi! So i saw this little "guy" or "creature"... i dont even have an idea what is this... is it part of David's body or what? [center] [IMG]http://i.imgur.com/43JylLn.png[/IMG] [IMG]http://i.imgur.com/CDoPk3g.png[/IMG] [/center] Im posting links not pictures, because they are big. Could someone check this scene? is it me, or something moves away there? It's the scene where David looks at the engineer climbing up, but you can see that on the picture. Please help me with this. *Picture Assistance by Freeze!