You'd be surprised how hard they ARE to miss. Most of the time, we were surprised by them.
Here's some info I dug up on them:
Like all arachnids, the Solifugids have eight legs, and their body is in two parts, a 'prosoma' equivalent to a thorax and an 'opisthosoma' or abdomen. Like scorpions, but unlike spiders, Solifugids have no narrow waste or 'pedicel'. Their chelicerae are extremely powerful, and are perhaps the most formidable jaws in the terrestrial animal kingdom in relationship to the size of the animal carrying them. They are not venomous but are fast and powerful. Their pedipals do not end in a claw but in a suctorial organ and their first pair of legs are long and thin and are not used for walking but are used as feeler like an insect uses its antennae, they are therefore referred to in some places as being 'antennaeform'. Their 4th pair of legs possess 5 (3 in the Hexisopodidae) 'malleoli' or 'racquet organs'. Their bodies and legs are hairy, they are generally 1-5 cms long (though Galeodes arabs often looks to be 12cm or more long when its legs are taken into consideration, and mostly uniform in colour, yellow, brown or black, though a few are patterned. They have a well developed tracheal system which helps them get the oxygen they need for their extremely active lives. They live predominantly in hot dry desert like areas, there are only 6 species in Europe and they all live in the Southern Europe only. They can stridulate (make a noise) by rubbing together a piar of horny ridges on the insides of their chelicerae.
*Note: Above when I said they were about the size of the palm of your hand, I was meaning with the legs. We never picked them up, and I myself was judging size based on the legs. I guess science measures the body length.
We also killed any of them that we found (after teasing them, making them bite stuff, etc.)